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Ensure Your Wines are Stable Before Bottling

By: Denise M. Gardner

It’s that time of year again: bottling time! The past year’s vintage is slowly starting to take up too much room in the cellar and now is the time for decision making in terms of preparing for the pending vintage.  Finalizing a good bottling schedule before harvest starts is an essential good winemaking practice, but bottling comes with its own set of challenges.

It is not uncommon for winemakers to express feelings of “not being able to sleep at night” when wines get bottled, as they are worried about possible re-fermentation issues.  As wine naturally changes through its maturity, it is easy to feel insecure about bottling wines, especially those wines that may have had challenges associated with it throughout production.

However, there are several analytical tests that winemakers can add to their record books every year to ensure they are bottling a sound product.  The following briefly describes a series of analytical tests that provide information to the winemaker about stability and potential risks associated with the product when it goes in bottle.

Bottling comes with its own set of challenges and risks, but several analytical tests can help put a winemaker’s mind to ease regarding bottle stability. Photo by: Denise M. Gardner

Basic Wine Analysis Pre-Bottling:

This first list is the bare minimum data that should be measured and recorded for each wine getting bottled, regardless of the wine’s variety or style.  Keeping accurate records of these chemistries is also helpful in case something goes wrong while the bottle is in storage or after it is purchased by a customer.

pH

pH is essential to know as it gives an indication for the wine’s stability in relation to many chemical factors including sulfur dioxide, color, and tannin.  For example, high pH (>3.70) wines provide an indication that more free sulfur dioxide is needed to obtain a 0.85 ppm molecular free sulfur dioxide content.  At the 0.85 ppm molecular level, growth of any residual yeast and bacteria in the wine should be adequately inhibited.

High pH wines tend to have issues with color stability.  At this point, color stability can be addressed by blending or with use of color concentrates (e.g., Mega Purple).  Keep in mind that if the wine is blended with another wine, all chemical analyses, including pH, should be completed on the blend (as opposed to average individual parts) prior to bottling.

Free and Total Sulfur Dioxide Concentration

In the United States, total sulfur dioxide is regulated and must fall under 350 mg/L for all table wines (CFR: https://www.ecfr.gov/cgi-bin/text-idx?SID=eddaa2648775eb9b2423247641bf5758&mc=true&node=pt27.1.24&rgn=div5#sp27.1.24.a).

However, the free sulfur dioxide concentration provides an indication to the winemaker regarding antioxidant strength and perceived antimicrobial protection.  To inhibit growth of yeast and bacteria during bottle storage, a 0.85 ppm molecular free sulfur dioxide concentration must be obtained.  The free sulfur dioxide concentration required to meet the molecular level is dependent on pH.  Therefore, free sulfur dioxide additions should be altered and based on a wine’s pH for optimal antimicrobial protection.

Analytically, it can be daunting to measure free sulfur dioxide as the wet chemistry set up looks intimidating.  However, many small commercial wineries have benefited from the integration of a modified aeration-oxidation (AO) system, and with a little practice, have been relatively successful at monitoring free sulfur dioxide concentrations.  A few wineries have worked to validate use of Vinmetrica’s analyzer (https://vinmetrica.com/), and found results comparable to those obtained by use of the AO system.

Residual (or Added) Sugar

Any remaining sugar in the bottle, whether through an arrested fermentation or direct addition, can pose a risk for re-fermentation post-bottling.  This is especially true if the winery lacks good cleaning and sanitation practices.  Nonetheless, it is a good idea to assess the sugar content pre-bottling to record a baseline value of the sugar concentration going into bottle.  If bottles were to start re-fermenting, a sugar concentration could be analyzed and used to compare against the baseline value in order to assess the potential of yeast re-fermentation.

For wineries with minimal residual sugar concentrations, a glucose-fructose analysis (often abbreviated glu-fru) is often used to help determine accurate sugar content.  For wines with added sugar an inverted glucose-fructose analysis may be required.

If you are concerned about potential risk for Brettanomyces (Brett) bloom post-bottling, it is usually encouraged to reduce the sugar content in the finished wine below 1% (<10 g/L sugar) in the bottle.

Malic Acid Concentration

While using paper chromatography to monitor malolactic fermentation (MLF) is useful, it does not give an accurate reflection of residual malic acid concentration.  In fact, some winemakers find that a paper chromatogram may show a MLF has been “completed,” but would prefer to have lower residual malic acid concentrations remaining in the wine.

During my time at an analytical company, 0.3 g/L of malic acid and below was considered “dry.”  This is typically a safe level of residual malic acid to avoid post-bottling MLF.

Volatile Acidity

Volatile acidity (VA) is federally regulated, and levels are indicated in the Code of Federal Regulations (CFR: https://www.ecfr.gov/cgi-bin/text-idx?SID=eddaa2648775eb9b2423247641bf5758&mc=true&node=pt27.1.24&rgn=div5#sp27.1.24.a).  For most states, with California as an exception, the maximum allowable VA for red wines is 1.40 g/L acetic acid (0.14 g/100 mL acetic acid) and for white wines is 1.20 g/L acetic acid (0.12 g/100 mL acetic acid).

Monitoring VA through production is a good indicator of acetic acid bacteria spoilage.  At minimum, wineries should record VA

  • immediately post-primary fermentation,
  • post-MLF,
  • periodically through storage (e.g., every 2-3 months) and
  • pre-bottling.

Whiling monitoring VA, sharp increases in VA should alarm the winemaker of some sort of contamination.  Typically, these increases are caused by acetic acid bacteria, which can only grow with available oxygen.

Alcohol Concentration

As a general rule of thumb, knowing the final alcohol concentration is a good idea.  Alcohol content helps determine a tax class for the wine and is required for the label.

 

Extra Analysis:

Titratable Acidity (TA)

All wines are acidic in nature as they fall under the pH 7.00.  However, titratable acidity (TA) acts as an indicator for the sour sensory perception associated with a given wine.  For example, two wines, Wines 1 and 2, with a pH of 3.40 may have different TAs.  If Wine 1 has a TA of 8.03 g/L tartaric acid while Wine 2 has a TA of 6.89 g/L tartaric acid, Wine 1 would likely taste more acidic (assuming all other variables are the same).

Titrations are an easy analytical testing method to learn and understand when testing wine’s chemistry. Photo by: Denise M. Gardner

Cold Stability

Cold stability tests are often recommended to ensure the wine is cold stable, and will, therefore, not pose a threat of precipitating tartrate crystals during its time in bottle.  Not all wines require a cold stability process (e.g., seeding and chilling).  Cold stability testing can be done prior to a cold stabilization step in order to avoid extraneous processing operations, saving time and money.

For more information on cold stability processes and testing, please visit Penn State Extension’s website: http://extension.psu.edu/food/enology/analytical-services/cold-stabilization-options-for-wineries

These crystals on this cork illustrate what can happen when a wine is not properly cold stabilized. While the tartrate crystals pose no harm to consumers, they may find the crystals unappealing or questionable. Photo by: Denise M. Gardner

Protein Stability

Additionally, haze formation is a potential risk post-bottling.  While hazes do not typically offer any safety threat to wine consumers, they often look unappealing.  Protein hazes tend to make the wine look cloudy.  Some varieties are more prone to protein hazes then others, and running a protein stability trial could minimize the risk for a protein haze in-bottle.

It is important to remember that due to the fact protein stability is influenced by pH, cold stability production steps should take place before analyzing the wine for protein stability and before going through any necessary production steps to make the wine protein stable.  This is due to the fact that cold stability processes ultimately alter the wine’s pH, and the chemical properties of proteins are influenced by the pH.

 

Analysis for Those that May Consider Bottling Unfiltered:

Yeast and Bacteria Cultures (Brett, Yeast, Lactic Acid Bacteria, Acetic Acid Bacteria)

Having a microscope in the winery can be a great reference point in terms of scanning for potential microbiological problems.  However, if the winery does not have a microscope, but knows that some microbiological issues or risks may exist in a wine, having a lab set test the wine on culture plates is a good indicator for potential growth risks during the wine’s storage.

If the wine is going to be bottled using a sterile filtration step, keep in mind that wines are not bottled sterile.  Assuming the absolute filtration method is working properly, the wine has potential to become re-contaminated with yeasts and bacteria from the point of which it exits the filter.  In fact, it is not uncommon for wines to pick up yeast or bacteria contamination during the bottling process.

Managing free sulfur dioxide concentrations can help inhibit any potential growth from contamination microorganisms if the proper antimicrobial levels (0.85 ppm molecular) are obtained at that wine’s pH and retained during the bottle’s storage.

4-EP and 4-EG Concentrations for Reds

For wines that may have had a Brettanomyces (Brett) bloom, knowing the concentrations of 4-EP and 4-EG in the wine going into bottle is a good result to keep on file.  If a Brett bloom occurs later in the bottle, it is likely (although, not guaranteed) that the volatile concentration of 4-EP and/or 4-EG may increase and confirm the problem.

Furthermore, evaluating a wine for 4-EP and 4-EG concentrations can also help isolate a possibility of Brett existence, especially if their concentrations are below threshold.  However, it should be noted that both compounds can also exist in wines that are stored in wood, even without a Brett contamination.

Double Check: PCR for Reds

Brett can be a tricky yeast to isolate and identify.  It is usually recommended to run multiple analytical tests related to Brett in order to confirm its existence or removal from a wine.  While culture plating identifies living populations of microorganisms, PCR cannot typically differentiate between live and dead cells as it is measuring the presence of DNA.  A microorganism’s DNA can get into a wine after yeast death and through autolysis.  Therefore, a positive PCR result for Brettanomyces is hard to confirm if the result includes live cells, dead cells, or a combination of both.

Culture plating can help confirm the presence of active, live cells, but the success rate of growing Brettanomyces in culture plates is variable.

Nonetheless, scanning wines by PCR for Brett can help winemakers isolate a general presence and risk of Brett in their wines.

Wine samples prepare for analytical evaluation. Photo by: Denise M. Gardner

Still Worried About Your Wine Post-Bottling?

Bottle sterility

Bottle sterility testing is helpful, especially when a winemaker wants to ensure wines have been bottled cleanly.  For this type of testing, it is best to sample a few bottles

  • at the beginning of a bottling run,
  • immediately before any breaks,
  • immediately after any breaks, and
  • at the end of a bottling run.

Bottles can, again, be evaluated under a microscope and evaluated for the presence of microorganisms.  Bottles can also be sent to a lab for culture plating.  The growth of yeasts or bacteria from culture plates at this stage indicates a failure of the sterile filtration system or contamination of the wine post-filtration.  Clean wines, obviously, should help put a winemaker’s mind at ease as it matures in bottle.

Ensuring a wine’s stability post-bottling is a challenge.  However, with proper cleaning and sanitation methods coupled with the right analytical records, winemakers can reduce their worry.  For information on any of these topics, please visit:

 

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Minimizing Spoilage of Wines in Barrel

By: Denise M. Gardner

The use of oak in the winery offers many options from winemakers.  With today’s availability of various oak products (i.e., chips, staves, powders), winemakers have more choices than ever before to integrate a wood component into their product.  However, the use of oak barrels remains an intrinsic part of most winery operations.  During the aging process, oak barrels have the potential to:

  • integrate new aromas and flavors into the wine.
  • add mouthfeel and/or aromatic complexity to the wine.
  • change the wine’s style.
  • add options and variation for future wine blends.

Additionally, the barrel room is often romantically viewed upon by consumers, and it is not uncommon for visitors to find barrel show cases in many tasting rooms, private tasting rooms, or while on a guided winery tour.

The barrel room at Barboursville Vineyards (VA) gorgeously catches the eyes of their visitors. Photo by: Denise M. Gardner

 

Oak fermenters at Robert Mondavi Winery (CA) that guests can see on their famous guided tour. Photo by: Denise M. Gardner

Nonetheless, barrels also offer challenges to wineries.  One of the most inherent challenges associated with a barrel program is maintaining a sanitation program.

The growth of spoilage yeast, Brettanomyces, is often discussed amongst wineries that utilize barrel aging programs.  However, additional spoilage yeast species such as Candida and Pichia have also been associated as potential contaminants in the interior of wine barrels (Guzzon et al. 2011).  Brettanomyces, commonly abbreviated as Brett, was first isolated from the vineyard in 2006 (Renouf and Lonvaud-Funel 2007) and until that point had most commonly been associated with the use of oak in the winery.  The growth of Brett in wine has the potential to impart several aromas as a result of volatile phenol [especially 4-ethylphenol (4-EP) and 4-ethylguaiacol (4EG)] formation in the wine.  Descriptors used to describe a Bretty wine include: barnyard, horse, leather, tobacco, tar, medicinal, Band-Aid, wet dog, and smoky, amongst others.  It should be noted that the presence of these aromas does not necessarily confirm that Brett is in the wine; there are other microflora, situations (e.g., smoke taint) or oak chars that can impart some of these aromas, as well.

Brettanomyces aroma descriptors. Image by: Denise M. Gardner

When barrels are filled with wine, it’s important to monitor the wine regularly for off-flavors while it is aging.  Wines should be regularly topped up with fresh wine to avoid surface yeast or acetic acid bacteria growth that can contribute to the volatile acidity (VA).  We usually recommend topping barrels up every-other-month.  Keep in mind that free sulfur dioxide concentrations can drop quicker in a barrel compared to a tank or wine bottle (MoreFlavor 2012) and free sulfur dioxide contractions should be checked (in conjunction with the wine’s pH) and altered as necessary to avoid spoilage.  Finally, when using a wine thief, both the internal and external part of the thief need cleaned and sanitized in between its use for each and every barrel to avoid cross contamination.  Dunking and filling the thief in a small bucket filled with cold acidulated water and potassium metabisulfite (acidulated sulfur dioxide solution) is a helpful quick-rinse sanitizer.

Barrels offer a perfect environment for microflora to flourish.  Wine barrels are produced from a natural substance (wood), which has its own inherent microflora from the point of production; obviously, barrels are not a sterile environment when purchased.  However, the structure of wood is rigid and porous, which provides nooks and crevices for yeast and bacteria to harbor within.  The porosity of the wood also makes it difficult to clean and sanitize, especially when compared to cleaning and sanitation recommendations associated with other equipment like stainless steel tanks.  Guzzon et al. (2011) found that barrels used over 3 years in production had a 1-log higher yeast concentration rate retained in the barrel compared to new and unused oak barrels.  This demonstrates the ideal environment within the barrel for retaining microflora over time, even when adequate cleaning and sanitation procedures are utilized in the cellar.

Common barrel sanitizers include ozone (both gas and aqueous), steam, hot water, acidulated sulfur dioxide, and peroxyacetic acid (PAA).  A study conducted by Cornell University on wine barrels used in California wineries found the use of sulfur discs, PAA at a 200 mg/L concentration, steam (5 and 10 minute treatments) to be effective sanitation treatments for wine barrels (Lourdes Alejandra Aguilar Solis et al. 2013).  In this same study (Lourdes Alejandra Aguilar Solis et al. 2013) ozone (1 mg/L at a 5 and 10 minute treatment) was also evaluated and found effective in most barrels tested, but a few barrels that did not show adequate reduction with the ozone treatment.  While the research conducted by Cornell indicated the potential lack of cleaning the barrel thoroughly before the ozone sanitation treatment, Guzzon et al. (2011) cited ozone’s efficacy is most likely caused by its concentration.  Both are important considerations for wineries.

Barrels should always be effectively cleaned of any debris and or tartrate build up before applying a sanitation agent.  This is essential to allow for maximum efficacy during the sanitation step.  High pressure washers, a barrel cleaning nozzle, and the use of steam are some options available to wineries in terms of physically cleaning the interior of barrel.  Additionally, some wineries use sodium carbonate (soda ash) to clean some of the debris (Knox Barrels 2016, MoreFlavor 2012) in addition to the use of a high pressure wash.  Always remember to neutralize the sodium carbonate with an acidulate sulfur dioxide rinse prior to filling with wine.

Dr. Molly Kelly from Virginia Tech University has previously recommended a 3-cycle repeat of a high-pressure cold water rinse, followed by high pressure steam before re-filling a used barrel and assuming the wine that came out of that barrel was not contaminated with spoilage off-flavors (Kelly 2013).  If the barrel is hot by the end of this cycle, it may be advantageous to rinse with a cold, acidulated sulfur dioxide solution before filling the barrel with new wine.  If there isn’t wine available to refill the barrel, it can be stored wet with an acidulated sulfur dioxide solution or using sulfur discs (Kelly 2013).

It is not usually recommended to store used barrels dry for long periods of time, and wineries can use an acidulated sulfur dioxide solution (top off as if it had wine in it) for long-term storage.  However, wineries that store their barrels dry need to rehydrate the barrels prior to filling with wine.  Check the cooperage for leaks, air bubbles, and a good vacuum seal on the bung.  Steam or clean water (hot or cold, overnight) are adequate rehydrating agents (Pambianchi 2002).  Barrels that leak wine offer harboring sites for potential yeast, bacteria, and mold growth, which can all act as contaminants to the wine itself.

It should be noted that contaminated barrels (barrels that produce a wine with off-flavors) may need extra cleaning and sanitation steps to avoid future contamination when the barrel is refilled.  It is typically recommended to discard barrels that have a recorded Brett contamination.  If the barrel has picked up any other off-flavors, especially during storage, it should probably be discarded from future wine fillings.

Barrels undoubtedly offer several challenges for wineries, including proper maintenance, cleaning and sanitation.  Nonetheless, engaging in good standard operating procedures for maintaining the barrel’s cleanliness can help enhance the longevity of the barrel and minimize risk of spoilage for several wine vintages.

 

References

Guzzon, R., G. Widmann, M. Malacarne, T. Nardin, G. Nicolini, and R. Larcher. 2011. Survey of the yeast population inside wine barrels and the effects of certain techniques in preventing microbiological spoilage. Eur. Food Res. Technol. 233:285-291.

Kelly, M. 2013. Winery Sanitation. Presentation at Craft Beverages Unlimited, 2013.

Knox Barrels. 2016. Barrel Maintenance.

de Lourdes Alejandra Aguilar Solis, M., C. Gerling, and R. Worobo. 2013. Sanitation of Wine Cooperage using Five Different Treatment Methods: an In Vivo Study. Appellation Cornell. Vol. 3.

MoreFlavor. 2012. Oak Barrel Care Guide.

Pambianchi, D. 2002. Barrel Care: Techniques. WineMaker Magazine. Feb/Mar 2002 edition.

Renouf, V. and A. Lonvaud-Funnel. 2007. Development of an enrichment medium to detect Dekkera/Brettanomyces bruxellensis, a spoilage wine yeast, on the surface of grape berries. Microbiol. Res. 162(2): 154-167.

 

Making Cleaning and Sanitation Practical for the Small Commercial Winery

By: Denise M. Gardner

While in the midst of harvest (and all the craziness that comes with it), I thought I’d take a week to remind people about proper cleaning techniques, improving sanitation, and why these two operations are essential for wineries.

I know many of you are ready to close this page now, but WAIT!

I have heard many excuses for short cutting on cleaning over the years.  Do any of the following sound familiar?

  • There is not enough time in the day to properly sanitize.
  • There are not enough employees to do all the work to properly clean. 
  • Cleaning would take all night to complete properly.
  • It’s not necessary to clean/sanitize with wine.
  • The wine will sell anyway.
  • Cleaning and sanitizing does not actually improve wine quality.
  • Sanitation is not really important.
  • Proper cleaning does not increase the price in which the wine can be sold.

If you or any of your employees have used at least one of these statements in the past, you could be suffering from poor cleaning and sanitation practices!

In all seriousness, having good cleaning and sanitation procedures can actually save the winery time and money in the long run.

In the height of harvest, I’m sure this is a tough sell.  But let’s consider some of these practical cleaning and sanitation suggestions for small, commercial wineries.

On the same page with cleaning vs. sanitizing

Let’s start with a review of definitions, as it can get very confusing.  Below are some general definitions taken from a series of sources (Fugelsang and Edwards 2007, Iland et al. 2007, Iland et al. 2012, Solis et al. 2013) to explain the differences between cleaning, sanitation, and sterilization.

  • Cleaning – the physical removal of dirt, debris or unwanted material (solid or liquid) from a surface
  • Sanitizing – a 99.9% (3 log) reduction of microorganisms
  • Sterilizing – the complete removal or inactivation of microorganisms

The wine industry is primarily focused on cleaning and sanitation protocols, as there are not many sterile practices utilized in winery operations (unless you are one of the lucky few wineries bottling aseptically).  Even if processors are using sterile filtration to remove yeast and bacteria from the wine, once the wine exits the filter, it comes in contact with equipment that is only sanitized (hopefully!).

Additionally, wine bottles or packages are not sterile when being filled.  Even new bottles can contain yeast or bacteria that can potentially contaminate a finished wine.  Hopefully, proper sulfur dioxide levels should keep this microorganisms at bay.

For all of these reasons, as the wine has the opportunity to come in contact with existing microflora on processing equipment, wine is bottled in a sanitized environment.

Remember proper sanitation is primarily having good cleaning protocols.  Cleaning should always precede sanitation. Failure to physically remove all of the debris from equipment, results in an inability to properly conduct sanitation procedures.

There are several different detergents (cleaners) and sanitizers that wineries can use effectively.  Example sanitizers include quarternary ammonium compounds (QUATS), peroxyacetic acid, chlorine dioxide, hot water, and steam.  Additionally, wineries can find use in an acidulated (citric acid) sulfur dioxide mixture.  However, all sanitizers should be selected specifically for the job at hand (Iland et al., 2012) with consideration towards the microbes that one is trying to avoid.

Most commercial wineries can really focus on improving cleaning practices to provide a step in the right direction towards improving quality and sanitation practices inside the winery.

If you think you may need some help in obtaining winery sanitation basics, please refer to this Northern Grapes Webinar by Randy Worobo on YouTube.  Or check out this PodCast by Hans Walter-Peterson and Chris Gerling from Cornell: Winery Sanitation Presspad Podcast, which focuses on preparation for harvest and including sanitation in that prep.

Cleaning harvesting equipment

While this is usually one of the places winemakers feel most complacent about, I would argue that this can be one of the most important places to take care in your cleaning and sanitation practices.

  • There is a lot of effort that goes into the growing season in order to adequately ripen wine grapes for many sensory nuances.  Additionally, the vineyard is the source of many microorganisms that enter the crush pad and cellar.  [For those that use mechanical harvesters, do not forget cleaning and sanitation of this vital piece of equipment (Pregler 2011).]  Giving the grapes a clean surface to encounter upon entering the winery ensures that all of that hard work is truly appreciated and preserved from the start of fermentation.
  • Without proper cleaning and sanitation practices, you are likely increasing the microbial populations of your wine before it even gets a chance to ferment.  Think about it.  After crushing/destemming a lot of rotting Pinot Grigio, Pinot Noir, or botrysized Riesling, how many people spray down the equipment (lightly) and move onto crushing the next lot of fruit even if the second lot is cleaner than the first?  Sometimes, the order of grape crushing cannot be avoided.  But how it is handled upon receiving can be altered.  If this is the case for your winery, and you are avoiding good cleaning and sanitation steps in between lots of fruit, you are cross contaminating your juice with, not only yeast and bacteria present in the rotted fruit, but also residual enzymes, proteins, and other by products that can alter wine chemistry in the clean fruit that follows.  Think about the potential production problems this can cause later on down the road: laccase browning, acetic acid development, off-flavor development, etc.  If such problems arise, it can cause labor and financial investment at a later time.
  • Residual foodstuffs (e.g., old grape skins, rice hulls, pulp) can contribute to off flavors within the finished wine.  Recent research has shown that there is potential for aromatically-intense varieties (i.e., Niagara, Concord, or Noiret) to leach their flavor compounds into more neutral varieties through absorption and diffusion of equipment-based plastic components that come in contact with the juice and wine (Smith 2014).  It is also possible for alien material (i.e., green matter, old rice hulls, and stuck fruit) to contribute to flavors in the final product that may be undesirable or challenging to fix.
  • Remember that rice hulls are a pressing aid primarily used for A) hard-to-press varieties to increase yield or B) bulk operations in which pressing time is of the essence.  Previous studies, such as the one found here, have shown a detriment in flavor and quality of wines pressed with rice hulls for certain varieties.  Additionally, rice hulls can be difficult to remove from the wine press and create potential microbial infection sites for later grapes/juice/wine.  It is recommended that the use of rice hulls be on aromatically intense or difficult-to-press varieties (e.g., many native varieties).  Use of rice hulls in grapes that have a lot of rot will not only help increase yield of the fruit, but also increase extraction and retention of rot byproducts, which can contribute to off-flavor development.
  • Proper cleaning can help maintain your equipment longer.  Over time, plant material can slowly degrade equipment.  Doing a little scrubbing and properly sanitizing repeatedly can help keep your equipment in relatively good condition.  Additionally, the longer debris is left on equipment, the harder it is to remove.
Figure 1: Preparing a small solution of acidulate sulfur dioxide to sanitize processing equipment before crushing/destemming and pressing operations. Photo by: Denise M. Gardner

Figure 1: Preparing a small solution of acidulate sulfur dioxide to sanitize processing equipment before crushing/destemming and pressing operations. Photo by: Denise M. Gardner

Properly maintaining harvest equipment also leads a good example for all of the other equipment in the winery.

Tanks, Barrels and Bottles

These are places in the cellar where it can get easy to take short cuts as opposed to properly cleaning or sanitizing equipment.

These are places in the cellar where it can get easy to take short cuts as opposed to properly cleaning or sanitizing equipment.

  • Remember that tartrate build up in tanks and barrels can make it difficult to properly sanitize the covered portion of the tank/barrel.  Make sure to first dissolve large tartrate deposits with hot water before going through a cleaning and sanitation cycle.  Without dissolving tartrates, the equipment is not going to get properly cleaned or sanitized.
  • When getting ready to fill a tank, remember to run a sanitizer through the tank first to minimize microbial populations on the interior surfaces that come in contact with the wine.  This helps ensure varietal flavor nuance and minimizes the risk for spoilage.  [Note: Some sanitizers are no-rinse sanitizers and do not require a rinse after the sanitation chemical is applied.  Other sanitizers may require a rinse following application.  Always check the directions pertaining to your sanitizer carefully before use to ensure it is being used properly for best efficacy, and always use proper protective clothing when handling sanitizer agents.]
  • Minimize harboring sites for insects and microbes within the cellar are a practice that can be done at the end of every shift.  During harvest, one big problem I see is dripping, dried juice or wine on the exterior of tanks or fermentation bins.  While this doesn’t seem like a big deal, it’s an attractive site for fruit flies, which also makes them attractive deposits for spoilage yeast and bacteria.  The objective of removing these places of dried juice/wine is to minimize insect infestation in the winery and avoid potential contamination of clean wines.
  • Barrels need cleaned prior to sanitation regimes like other pieces of equipment.  Many barrel cleaning systems are automatic and can be an efficient way to clean the interior of barrels.
  • Barrels are porous and have a lot of grooves inside of them, which can make it difficult to properly clean and sanitize.  It is important to note that due to the nature of the barrel, it cannot be sanitized in a way that a stainless steel tank can be sanitized.  However, there are many different cleaning and sanitation options for barrels out there, some of which are explored in this Appellation Cornell newsletter from 2013.  This study evaluated natural barrel microflora (yeast, including Zygosaccharomyces and Brettanomyces) before and after a sanitation regime was conducted.
  • Sulfur wicks are a good way to treat the interior surface of the barrel, but this practice does not penetrate into the interior of the wooden staves (Iland et al. 2007).  Also, ensure that the wick is not submerged below any left over water at the bottom of the barrel, as it may extinguish the wick (Iland et al. 2007).  Make sure the bung is tightly sealed for best efficacy of a sulfur wick (Rieger 2015).
  • Bottling lines are not immune to cleaning.  In the food industry, it is commonly noted that most contamination comes from the environment in which the food is processed.  This can happen in wine processing, as well.  Dust on the bottling line can harbor yeast and bacteria that can be disturbed or moved into the air during large movements, like when bottling a finished wine.  Keeping the bottling line clean is a good way to help minimize contamination during bottling operations.

Small Steps That a Commercial Winery Can Take to Improve Cleaning and Sanitation

Being a smaller or boutique sized winery can definitely have its advantages in the cleaning and sanitation world.  It’s easy to get creative in terms of improving efficiency, use of, and efficacy of cleaning and sanitation practices.  Below are some practical solutions for wineries struggling to incorporate cleaning and sanitation practices in the winery.

Use brushes, like Perfex brushes, to properly scrub equipment during cleaning operations.  These are especially helpful when getting that pesky debris off of processing equipment.

Color code brushes or cleaning materials to emphasize their use and make it easier on your employees.  By keeping the necessary supplies handy and easy to use, efficiency is likely to improve, which can actually help improve the quality of cleaning operations.  Typically, white brushes are reserved for food-contact surfaces (the part of the equipment that actually comes in touch with food) during sanitation steps.  Yellow brushes can be used for environmental cleaning (non-food-contact surfaces like the exterior of tanks).  Other colors can be purchased for additional specific purposes: detergent only, sanitizer only, etc. Keep the brushes handy during all processing operations.

Figure 2: Perfex Brushes that are great for cleaning and minimize bacteria retention.

Figure 2: Perfex Brushes that are great for cleaning and minimize bacteria retention.

There is a great article from Food Engineering on the power of color coordination in the food industry, which you can read here.

Consider keeping your cleaning and sanitation system on wheels.  While in Oregon, I found it clever how larger wineries kept their fittings on mobile units to aid in availability, cleaning, and organization (Figure 3).  While this concept may be helpful to some wineries, I think it can also be applied to cleaning materials.  Keeping cleaning materials isolated to a mobile until allows for quick use and organization throughout the entire production facility and minimizes needless travel time to walk back and forth towards where supplies may be kept.  Examples, below, for how to improve mobility of your cleaning supplies are given in Figure 4.

Figure 3: Mobile unit for holding cellar fittings is a great idea for easy organization, cleaning, storage, and use of fittings throughout a cellar. (Looking at mobile stand from the top) Photo by: Denise M. Gardner

Figure 3: Mobile unit for holding cellar fittings is a great idea for easy organization, cleaning, storage, and use of fittings throughout a cellar. (Looking at mobile stand from the top) Photo by: Denise M. Gardner

 

Figure 4: Utility carts like this plastic one from School Outfitters or the metal one from Grainger can be easy additions to hold necessary cleaning supplies like citric acid/sulfur dioxide and pH strips, as well as hang spray bottles or hold gloves for cleaning. Carts can be easily moved and stored in the cellar for convenience.

Figure 4: Utility carts like this plastic one from School Outfitters or the metal one from Grainger can be easy additions to hold necessary cleaning supplies like citric acid/sulfur dioxide and pH strips, as well as hang spray bottles or hold gloves for cleaning. Carts can be easily moved and stored in the cellar for convenience.

You do not need to use fancy (or expensive!) cleaners or sanitizers all of the time in the winery.  For quick clean ups, use warm water mixed with potassium carbonate to get stuck or sticky material off of equipment.  Use with caution as it can get slippery!

Follow a potassium carbonate rinse with a warm water rinse to remove the solution from equipment and environmental surfaces.

Acidulated sulfur dioxide (Figure 5) can act as a quick sanitizer as well, and is easy to make up and use in the winery.  Plus, citric acid, sulfur dioxide, and water are found in wine and will not have an effect on wine quality or flavor.

Figure 5: Keeping acidulated sulfur dioxide handy can be a quick sanitation solution during processing days. Photo by: Dr. Rob Crassweller

Figure 5: Keeping acidulated sulfur dioxide handy can be a quick sanitation solution during processing days. Photo by: Dr. Rob Crassweller

Finally, I always recommend wineries keep a supply of 70% ethanol in a spray bottle handy for quick cleaning solutions.  Ethanol can be used to clean up small spills, quickly rinse sampling valves before and after sampling, or act as an exterior sanitizer towards things like wine thieves, sampling pipettes, and lab benches where one is running analysis.  This is an easy chemical to keep on a mobile cart or scattered throughout the winery.  However, be sure to purchase food grade ethanol from a chemical supplier and dilute down to ~70% with non-chlorinated water.

Cleaning up at the end of a processing day makes the start up for the next processing day a lot easier.  If the equipment is clean to start, then all you have to do is run a quick sanitizer through the equipment before the start of processing operations.

Use hot water to rinse your equipment and make sure your hose has good pressure.  Cold water is definitely energy efficient, however, hot water can help remove a lot of debris quicker and make any potential scrubbing easier.  Be cautious of the metal on equipment heating up with use of hot water.  Also, increasing hose pressure can help dislodge any debris from equipment, which can save time during cleaning operations.

On large processing days (those days when 3 or 4 varieties are being crushed at the winery), designate the day to processing and wait until the next day to complete other operations that can be delayed.  Now, some flexibility needs to be made for things like punch downs or pump overs.  However, teamwork is key: punch down time can be reduced if there is more than one punch down tool available for employees to use.  Juice analysis (pH, TA, Brix, and YAN) is time sensitive, because if the juice starts going through spontaneous fermentation, the results of these chemical indices will change.  However, obtaining all of the juice samples from all lots of incoming fruit before starting analysis can save your employees time and avoid splitting up duties during a processing day.  With 3 employees, one person could run analyses while the remaining 2 finish cleaning up at the end of a processing day.  Reserve racking or moving wines for days when a little less is going on in the cellar unless it is absolutely necessary to open up space in tanks for incoming fruit.

Minimize barrel-to-barrel or tank-to-tank contamination by having small sanitation vessels/buckets (filled with sanitizer) handy and isolated for cleaning/sanitation use.  Use a bucket filled with acidulated sulfur dioxide solution to submerge (and fill) your wine thief in prior and after each barrel sample.  For smaller samples, consider using one-time-use or disposable pipettes (Figure 6).  If you have a 70% ethanol solution in a spray bottle, the metal fittings at the end of hoses can be quickly sprayed in between barrels when transferring barreled wine into a tank or transferring wine from a tank into barrels to help minimize cross contamination (Illand et al. 2007).

Figure 6: Serological or disposable pipettes are a great way to avoid cross contamination when smaller samples are needed. Photos from BioVentures.

Figure 6: Serological or disposable pipettes are a great way to avoid cross contamination when smaller samples are needed. Photos from BioVentures.

Check to see how clean your equipment is with quick testing strips like Pro-Clean Protein Residual testing strip by Hygiena.  These testing strips are a good indicator on how well your cellar crew is cleaning equipment.  The problem with protein test strips, like the one shown, is that it will detect all organic matter (Iland et al., 2007).  It does not represent live or viable microorganisms; there are rapid tests available that may be more representative of microorganism populations.

The video below indicates the ease in which these are to use:

Other options include luminometers like Hygiena’s SystemSURE Plus or 3M Clean-Trace (Rieger 2015), which are also non-specific, but can indicate the cleanliness of a contact surface that is swabbed properly.

While cleaning and sanitation may seem arduous, most wine quality problems I encounter – including funky off-flavors that are challenging to identify, presence of VA, large quantities of wine affected by cork taint, and lack of varietal character – could be primarily avoided with more routine and better cleaning operations.  Improving cleaning and sanitation operations can be a step in the right direction for wineries to improve quality associated with their business.

Resources

Iland, P., N. Bruer, A. Ewart, A. Markides, and J. Sitters. 2012. Monitoring the winemaking process from grapes to wine: techniques and concepts. 2nd Ed. Patrick Iland Wine Promotions Pty Ltd. Campbelltown, Australia. ISBN: 978-0-9581605-6-8.

Iland, P., P. Grbin, M. Grinbergs, L. Schmidtke, and A. Soden. 2007. Microbiological analysis of grapes and wine: techniques and concepts. Patrick Iland Wine Promotions Pty Ltd. Campbelltown, Australia. ISBN: 978-0-9581605-3-7.

Pregler, B. Nov 2011. Industry Roundtable: Cellar Sanitation. Wine Business Monthly.

Rieger, T. Oct 2015. Microbial Monitoring and Winery Sanitation Practices for Quality Control. Wine Business Monthly.

Smith, JC. 2014. Investigating the Inadvertent Transfer of Vitis labrusca Associated Odors to Vitis vinifera Wines. Retrieved from Electronic Theses and Dissertations for Graduate School: Penn State: https://etda.libraries.psu.edu/catalog/23501.

Solis, M.L.A.A., C. Gerling, and R. Worobo. 2013. Sanitation of Wine Cooperage using Five Different Treatment Methods: an In Vivo Study. Appellation Cornell. 2013-3.

Production Tips for the Home Winemaker

By: Denise M. Gardner

Home winemaking and home brewing can be some fun hobbies for enthusiasts or amateur growers and winemakers.  However, most home winemakers experience the same set of problems year after year without practical solutions for how to fix their wines or avoid challenges during production.  The following blog post discusses some possible considerations when making wine at home.

Concentrate – Grapes – or Juice

One thing to note is that concentrates are produced and manufactured with a pretty high success rate that the fermentation will complete with some sort of noticeable quality resembling wine.  These end up being the best product to use as an introductory fermentation base for those just starting to learn about the winemaking process.  The concentrate is simple: pour into the fermentation vessel and “just add water and yeast.”

The problem with concentrates is that they are easily identifiable, meaning the finished wines have a specific taste and quality standard that is noticeable sensorially regardless of the variety or source of the concentrate.  These wines will likely appear “simple” with nuanced fruit characteristics and a strong perception of alcohol.

However, when home winemakers switch to purchasing bulk juice or grapes, many new fermentation problems can arise that they did not experience during their use with concentrates.

This is due to the fact that bulk juices (purchased from a broker or home winemaking supply store) may contain preservatives (i.e., sulfur dioxide) that can make the initiation of fermentation more challenging.  Additionally, juice and grape quality is dependent on the source and how long the material was in storage before it arrives to the home winemaker’s fermentation vessel.

With juice and grapes, you are also dealing with the native microflora (e.g., yeast and bacteria), some of which can also be spoilage microorganisms, which can have numerous effects on fermentation kinetics and the finished wine quality.

However, using grapes or bulk juice as the starting base will provide a finished product that is more representative of where the grapes were grown (i.e., terroir representation) and provide the winemaker with more options for making the product unique.

Sanitation

Basic sanitation is what many home winemakers struggle with the most during fermentation and wine storage.

While most commercial sanitizers are not available to home winemakers, basic cleaning and sanitizing principles can easily be applied to home winemaking practices.

First, always make sure equipment is pulled apart and fully cleaned with hot water, a small (very small!) amount of non-scented dish soap, and some good, old fashioned elbow grease.  Removing debris and build up from all of the processing equipment improves the efficacy of a sanitizer.  Cleaning is at least 95% of sanitation, and this theory is true in home winemaking as well.

After the equipment is properly cleaned and rinsed with hot water, sanitation can follow.  Using a citric acid – sulfur dioxide blend in cold water is a good no-rinse sanitizer that home winemakers can utilize.  However, it is important that home winemakers take the care and precaution to ensure safety associated with using volatile sulfur dioxide.  Volatile sulfur dioxide is a lung irritant and can cause serious health issues if used improperly.  People with asthma or other lung-related conditions should not come in contact with potassium metabisulfite or sulfur dioxide.  For more information pertaining to how to properly use sulfur dioxide, please refer to Penn State’s Wine Made Easy Fact Sheet and your potassium metabisulfite supplier.

The citric acid – sulfur dioxide sanitizer is a no-rinse sanitizer.  This means that after the equipment has been sanitized, the juice or wine can come in contact with the equipment without any worry by the home winemaker.  Both citric acid and sulfur dioxide are naturally found in wine, so its use should not alter the flavor of the wine in any way.

bottles cleaned and sanitized

Wine bottles cleaned and sanitized prior to bottling. Photo by: Denise Gardner

Use Nutrients during Fermentation

Many home winemakers use non-specific yeast nutrients during fermentation.  However, the research and commercial industry worlds, we have started to learn that nutrient additions need to be specific towards the fermentation. Look to see if you can find commercial suppliers of yeast nutrient from companies like Beverage Supply Group, Christian Hansen, Enartis, Laffort, or Lallemand (to name a few of the suppliers).  Some home winemaking supply stores will carry small quantities of these products, and they are worth the purchase.

At minimum, using a yeast hydration nutrient (like GoFerm or an equivalent) will help to start the fermentation positively.  Complex nutrients (like Fermaid K or an equivalent) are typically recommended (up to a certain point) before using DAP.

Use of Fermaid K as a complex nutrient addition during primary fermentation. Photo by: Denise Gardner

Use of Fermaid K as a complex nutrient addition during primary fermentation. Photo by: Denise Gardner

If you can find a way to measure yeast assimilable nitrogen, or YAN, then nutrient additions can be made in specific quantities, using specific products (i.e., hydration nutrients, complex nutrients, or DAP) at the start and 1/3-of-the-way-through fermentation.  Utilizing the supplier’s guidelines for the rates of additions of your products, based on the starting YAN concentration, is a good way to minimize the risk of the wine tasting like rotten eggs or canned vegetables.

Manage Oxygen Exposure

Winemaking is tedious.  It requires the winemaker to constantly check and monitor the wine to ensure that things have not gone awry.

Home winemakers should try their best to minimize long-term oxygen exposure.  Using vessels to minimize surface area at the wine-oxygen interface will help reduce the risk of acetic acid bacteria contamination and growth, which contribute to the volatile acidity (i.e., the acetic acid – or vinegar – and nail polish flavors) of a wine.

If you need to “top up” carboys, use sanitized marbles to “push” the volume of the wine up into the neck of the carboy.  This helps minimize the surface area at the oxygen interface.

Wine carboys chilled and topped up to minimize oxygen exposure and preserve the wine. Photo by: Denise Gardner

Wine carboys chilled and topped up to minimize oxygen exposure and preserve the wine. Photo by: Denise Gardner

Avoid letting the wine “sit” without an active primary fermentation or malolactic fermentation (MLF).  Make sure when both of these fermentations are complete, properly treat the wine with potassium metabisulfite to ensure preservation and stability.

Keeping the wines stored in a cool location will help minimize bacterial growth or yeast spoilage, while preserving the wine.

Bottling the wines as soon as you can post-production can help ensure quality and stability.

Fully bottled wine. Photo by: Denise Gardner

Fully bottled wine. Photo by: Denise Gardner

Avoid Making Wines in Aromatic Environments

One problem that some home winemakers face is aromatic absorption associated with the odor of the environment in which the wine was produced.  This tends to be a problem when wines are made in an unfinished basement.

Wines are alcoholic solutions, which can absorb surrounding odors.  As unfinished basements tend to have that “wet basement” odor, the wine will likely absorb that aroma and flavor into the finished product.  However, many people may not be aware of the flavor until after the wine is removed from the odorous environment.

More Resources

These are just a few solutions pertaining to home winemaking situations.  However, you can find more resources, including “how to” book recommendations on the Penn State Extension Enology website.

Need more help in learning how to identify wine problems?  Check out some of Penn State’s local workshops pertaining to wine defect identification.  The next workshop is coming up on June 9th, 2016!

Stabilizing Wines in the Cellar

By: Denise M. Gardner

The long months post-harvest require regular attention by cellar staff and winemakers to ensure that wine quality is upheld through storage conditions. Wine stability, while somewhat nebulous, is essential to obtain in order to ensure the wine’s quality will be upheld post-sale.  Below is a list of cellar maintenance practices that are recommended in preparation before the growing (and bottling) season.

Monitor Sulfur Dioxide Concentrations

Now (i.e., the winter and spring months) is a good time to regularly check sulfur dioxide concentrations of wines sitting in tanks and barrels waiting to get bottled.  At minimum, wines should be checked once a month for free sulfur dioxide concentrations.  Some winemakers opt to check barreled wines every other month in order to minimize frequently opening the barrel.

Proper sanitation and sampling is required for best analytical results:

  • Use clean sampling bottles when taking wine samples
  • Make sure that you sanitize any valves or sampling ports before and after releasing a sample from a tank.  At the very least, you can use a food-grade alcohol solution spray or a citric acid-sulfur dioxide mix as a sanitizing agent.
  • Properly clean and sanitize wine thieves or other sampling devices each time you use it to take a sample from a barrel or the top of tank.  Warm water is not enough to sanitize a wine thief.  We recommend using a citric acid-sulfur dioxide mix for quick dipping in between barrel sampling.

For wines that have completed primary fermentation and/or malolactic fermentation, maintaining a molecular free sulfur dioxide concentration is helpful to reduce the risk of yeast and bacterial spoilage.  For a review on sulfur dioxide and making sulfur dioxide additions, please refer to this Penn State Wine Made Easy fact sheet.

It is essential to clean and sanitize your wine thief in between sampling from barrels. Photo from: Denise M. Gardner

It is essential to clean and sanitize your wine thief in between sampling from barrels. Photo from: Denise M. Gardner

Cold (Tartrate) Stabilization

Cold stabilization is often utilized to avoid the precipitation of tartrate crystals, which is common in instable wines at cooler temperatures.

In 2012, Virginia (Smith) Mitchell, now head winemaker at Galer Estate Winery, wrote a primer on cold stabilization techniques available for wine producers: http://extension.psu.edu/food/enology/analytical-services/assessment-of-cold-stabilization  This primer covered everything from how to analyze for cold stability to the use of carboxymethylcellulose (CMC) to avoid tartaric acid crystallization in wine.

Prior to putting a wine through cold stabilization, it is worth the time and effort to analyze the wine for cold stability.  Not all wines end up having cold stabilization problems.  For those wines that do not, going through the cold stabilization process can actually minimize wine quality by stripping out delicate aromas and flavors, or altering taste or mouthfeel attributes of the wine.  This doesn’t touch upon the amount of wasted time and effort to cold stabilize wines that are otherwise cold stable.

The above report recommends several testing procedures to ensure tartrate stability of a wine.

With the relatively warmer 2015-2016 winter, many winemakers may need to turn to artificial chilling in order to cold stabilize their wines properly.  Again, this could be used as an argument to test wines prior to cold stabilization to minimize the use of electricity and to better manage the flow of wines in and out of the cold stabilization tank.

Wines that do undergo cold stabilization will likely have changes in pH and titratable acidity (TA) that can ultimately affect other parameters of the wine: protein (heat) stability, color, sulfur dioxide concentrations, and volatile acidity.  It is prudent to check these components analytically following the cold stabilization process.

Protein (Heat) Stabilization

Proteins in wine can elicit hazes in wines post-bottling that may be off-putting to some consumers.  While the proteins cause no effect on wine quality, they do cause an alteration in the appearance of the wine.  Some varieties, like Gruner Veltliner, have naturally high concentrations of proteins, and, therefore, require a more aggressive approach to protein fining.  Other varietals, however, may not require protein fining with bentonite at all.

Wines should undergo protein (heat) stability after they are cold stabilized due to the fact that cold stabilization will affect the acidity (pH and TA) of the wine, and therefore, alter protein stability properties of the wine.  Again, winemakers are encouraged to check the wine for protein stability prior to treating a wine with bentonite.

Bentonite is a fining agent used to bind any proteins in a wine that would otherwise be considered unstable.  However, if the addition of bentonite is unnecessary (i.e., the wine is protein stable and does not provide a component for bentonite to bind to, bentonite can bind to other components in the wine, most specifically: aroma and flavor active compounds.  While this has been shown in the research literature, it is unclear how detrimental the loss of aromatic compounds is to the wine (Marchal and Waters 2010). Additionally, bentonite additions have been noted to strip color out of rosé and red wines (Butzke 2010).

A summary from UC Davis on heat stability testing can useful to understand the positive points and limitations of protein stability testing.  Protocols for heat stability tests can be found here from Dr. Bruce Zoecklein.  Additionally, ETS Labs has provided a small summary of how to interpret heat stability results, which can be helpful for wineries that are not used to reading analytical results on this test.

Additionally, wineries can submit wines to ISO-accredited labs for a bentonite trial in which the lab pinpoints the exact concentration of bentonite needed to heat stabilize the wine.  This may be helpful to avoid making too little or too much bentonite additions, which costs time and labor in the winery.

Bench Trials

Bench trials may be needed to determine how much bentonite is needed to obtain protein stability of your wine. Remember to use the same source and lot of bentonite in both your bench trials and commercial application. Photo from: Denise M. Gardner

Finally, if wineries are conducting their own bench trials, they are encouraged to use the same lot of bentonite in both the trials and the commercial application (Marchal and Waters 2010).  This is due to the natural variability associated with most bentonite products.  Finally, unless otherwise stated by the supplier, bentonite should always be blended in chlorine-free, hot (60°C, 140°F) water (Butzke 2010), and allowed to cool to room temperature so that the bentonite can swell.  Allowing the slurry to cool will ensure that the wine is not exposed to a hot slurry.

 

References Cited

Butzke, C. 2010. “What Should I use: sodium or calcium bentonite?” In: Winemaking Problems Solved. Christian E. Butzke, Ed. Woodhead Publishing Limited and CRC Press, Boca Raton, FL. ISBN: 978-1-4398-3416-9

Marchal, R. and Waters, E.J. 2010. “New directions in stabilization, clarification and fining of white wines.” In: Managing wine quality, volume 2. Andrew G. Reynolds, Ed. Woodhead Publishing Limited, Great Abington, UK. ISBN: 978-1-84569-798-3

Additional Resources

Iland, P., N. Bruer, A. Ewart, A. Markids, and J. Sitters. 2012. Monitoring the winemaking process from grapes to wine: techniques and concepts, 2nd edition. Patrick Iland Wine Promotions Pty. Ltd., Adelaide, Australia. ISBN: 978-0-9581605-6-8.

Penn State Extension Wine Made Easy: Sulfur Dioxide Management: http://extension.psu.edu/publications/ee0093

Penn State Extension: Assessment on Cold Stabilization: http://extension.psu.edu/food/enology/analytical-services/assessment-of-cold-stabilization

UC Davis: Heat Stability Testing: http://wineserver.ucdavis.edu/pdf/attachment/88%20stability%20tests%20and%20haze%20formation%20.pdf

Virginia Tech: Protein Stability Determination in Juice and Wine (1991): http://www.apps.fst.vt.edu/extension/enology/downloads/ProteinS.pdf

ETS Labs: Interpreting Heat Stability Tests: https://www.etslabs.com/assets/PTB011-Interpretation%20of%20Heat%20Stability%20Results%20and%20Turbidity%20Readings.pdf

 

Brett: The Good, The Bad, and The Ugly

By: Denise M. Gardner

The age-old controversy over the existence of Brettanomyces and its impact on wine quality continues to be a hot button topic in the wine industry.  Many will argue its ability to contribute to style as part of the natural terroir associated with where the grapes were grown.  Others point to the general lack of fruit flavor in Brett-rich wines, and common negligence to winery sanitation.

The truth?

As is the case of many wine production topics, it is likely that the truth lies somewhere in the middle, but the love-hate relationship with Brettanomyces lives on.

What is Brettanomyces (aka Brett)?

Brettanomyces bruxellensis (commonly known as Brett) is a yeast commonly found in wine, which may also be referred to in the wine literature as the Dekkera species.  While believed to come from the vineyard, it was first isolated from grapes post-veraison only recently: in 2006 (Renouf and Lonvaud-Funel, 2007).  Brett is also used and found in other fermented beverages including beer, hard cider, and distilled spirits.

In the winery, the use of wood has been identified as a primary source of Brettanomyces.  In fact, many report that new oak barrels have potential to bring Brett into the winery.  This is significant to wine producers, because it was originally thought that only old, used barrels could provide contamination sources of Brett.

However, knowing that Brett can come into the winery as native microflora to the wine grapes, it is probable to assume that any winery may have Brett populations within the production area.  Therefore, it is important for wineries to determine a way to manage Brett during various stages of wine production.

What does Brett do to wine?

Brett yeast typically imparts flavor characteristics to the wine, which can commonly be described using the following descriptors, although others exist:

  • Barnyard
  • Horse
  • Leather
  • Tobacco
  • Tar
  • Medicinal
  • Band-Aid
  • Wet Dog
  • Vomit
  • Plastic or Burnt Plastic
  • Smoky

Brett Aroma

These flavor descriptors are linked to the common generation of 4-ethyl guaiacol (4-EG) and 4-ethyl phenol (4-EP).  In some cases, concentrations of isovaleric acid have also been identified and quantified.  These aromatic/flavor compounds are developed as part of Brett’s metabolism.

Additionally, many winemakers have reported a “metallic bitterness” in the finish of many Brett-infected wines (Henick-Kling et al. 2000).

Regardless of its exact descriptors, the development of Brett-like flavors often leads to a suppression of the fruit flavors, native to the wine variety.  In many cases where people consider Brettanomyces a flaw, it is due to the fact that there are no residing fruit flavors left in the wine, as Brett tends to mask and dominate the wine flavor.

How does Brett survive in wine?

Brett has the unique ability to “hang out” in the wine until an opportune moment presents itself for growth and proliferation.  Brett can survive in wines, a low pH environment, is tolerant of sulfur dioxide, and does not appear hindered by relatively high concentrations of alcohol (~14%) (Iland et al. 2007).  Additionally, Brett can utilize many substrates that Saccharomyces yeast (i.e., wine yeast) cannot: malic acid, ethanol, wood sugars, higher levels of fructose, residual amino acids and nitrogen sources.  Therefore, a wine could be considered “dry” (<1.0 g/L residual sugar) and still experience a Brett bloom at some point during its production.

One key problem with Brett is the fact that it often “surfaces” post-bottling (Coulter 2012).  Therefore, if wineries are not conducting adequate analytical and sensory testing pre-bottling, or utilizing proper sterile filtration techniques, they may be bottling a Bretty wine without knowing it!  Coulter (2012) found that it is not unusual for only some bottles within a batch of wine bottled in the same day to have Brett blooms while others do not.  Many note that Brett growth is stimulated by oxygen ingress, and Coulter concluded that the variability associated with the oxygen transfer rate of natural cork closures may contribute to post-bottling variability of Brett blooms.  However, it is important to note that the incidence of Brett growth is not isolated to wines bottled with a natural cork closure.

General Prevention of Brettanomyces in the Winery

It is difficult for wineries to manage Brett once it has surfaced in the winery.  Wineries are encouraged to avoid purchases of old barrels unless they are aware and confident in the seller’s cleaning practices.  Even well-sanitized wineries may harbor Brett populations, and should not be considered risk-free.

Maintaining adequate environmental and equipment sanitation practices is helpful to minimize Brett in the winery.  Many industry members recommend proper barrel sanitation using steam or ozone to prevent or manage Brett.

Despite a winery’s best efforts, Brett is a possibility.  In incidences when there is a Brett bloom in a barrel, it is best to isolate those barrels from others.  Avoid contaminating “clean” barrels or tanks.  Using sterile filtration prior to bottling is recommended for wines that contain Brett to prevent blooms in the bottle.

Winery cleanliness and sanitation is an important component in reducing microbial contamination risks throughout various stages of wine production.  The above image shows an example of good cleaning and sanitation practices.  Photo by: Denise M. Gardner

Winery cleanliness and sanitation is an important component in reducing microbial contamination risks throughout various stages of wine production. The above image shows an example of good cleaning and sanitation practices. Photo by: Denise M. Gardner

References Cited

Coulter, A. 2012. Post-bottling spoilage – who invited Brett? Practical Winery & Vineyard Journal.

Henick-Kling, T., C. Egli, J. Licker, C. Mitrakul, and T.E. Acree. 2000. Brettanomyces in Wine. Presented at: The Fifth International Symposium on Cool Climate Viticulture and Oenology, 16-20 January, 2000 in Melborne, Australia.

Iland, P., P. Grbin, M. Grinbergs, L. Schmidtke, and A. Soden. 2007. Microbiological analysis of grapes and wine: techniques and concepts. ISBN: 978-0-9581695

Renouf, V. and A. Lonvaud-Funnel. 2007. Development of an enrichment medium to detect Dekkera/Brettanomyces bruxellensis, a spoilage wine yeast, on the surface of grape berries. Microbiol. Res. 162(2):154-167.

Reflections: Winemaking at Penn State

By: Denise M. Gardner

I can officially say that I have now been involved with 5 harvests here at Penn State, with my first harvest in 2011.  Returning to Pennsylvania from California in 2011 could not have been a greater challenge to an incoming newbie, and I think it will forever be one of the most difficult vintages I have had the experience to deal with to date.  Not only did I manage to lose an entire lot of finished wine down the drain (long story…), but I recognized the need to bring PA-produced research wines to Pennsylvania’s growing wine industry during a daunting season from a weather perspective.  Additionally, I saw an opportunity to educate students on how to make wine while they helped me process fruit from the research vineyards.  In that first year, 5 lucky college seniors helped me process about 8 different varieties from the NE-1020 “multi-state evaluation of wine grape cultivars and clones” project, which was being financially supported by a multi-state SCRI grant.

Looking back today, I now see that the 2011 vintage provided me with a starting point to work with students and a series of winemaking lessons for future vintages that I continue to recall even today.

I was actually one of those bright-eyed students back in my younger days.  I stumbled upon Penn State Extension and Mark Chien by pestering local Extension educators on how to grow grapevines.  I still recall the many opportunities Mark, specifically, provided for me despite my age or lack of wine knowledge.  Mark taught me how to plant a vineyard, from site selection to digging holes for a trellis, how to monitor vine growth through proper pruning techniques, how to ferment grapes into wine, and the various stages involved in production that went beyond the basic texts on how to make wine.  I connected with industry members and was awarded an experience to intern at Lallemand in Toulouse, France before I reached my freshman year in college.

Figure 1: Extension Enologist, Denise Gardner, developed an interest in wine grape growing and production throughout high school.  Photos, from left to right, include an annual fermentation lesson during a high school agriculture class, building a trellis system at the local high school, grape vines after 2 years of growth at the high school vineyard, and a lesson from past Extension Viticulturist, Mark Chien, on how to properly prune grapevines at a PA vineyard.  Photos provided by: Denise M. Gardner

Figure 1: Extension Enologist, Denise Gardner, developed an interest in wine grape growing and production throughout high school. Photos, from left to right, include an annual fermentation lesson during a high school agriculture class, building a trellis system at the local high school, grape vines after 2 years of growth at the high school vineyard, and a lesson from past Extension Viticulturist, Mark Chien, on how to properly prune grapevines at a PA vineyard. Photos provided by: Denise M. Gardner

When I arrived to Penn State in 2011, I had a memory of the opportunities Extension awarded me and a goal of working with students that may have an interest in wine production.  I still laugh when I recall a number of students that experienced a harvest at a local winery, only to tell me it was “the hardest thing they have ever had to do.”

While many may not make the connection, food science offers an incredible foundation of knowledge that is beneficial for winemakers and those whom wish to go into fermented beverage production.  Students engage in a series of classes to develop a foundation in chemistry, microbiology, and biotechnology.  Additionally, they learn important processing parameters that are affiliated with winemaking: sanitation, quality control practices, safety when processing, proper sampling techniques, and experimental practices to improve food/beverage products.

For that reason, the annual harvest and production of wine with use of undergraduate and graduate students’ support has blossomed into many positive ventures:

  • Since 2010, Penn State Food Science and several Pennsylvania wineries have sponsored student co-ops at wineries during vintage seasons. These experiences educate students in wine production, and specifically provided venues for “real world” experiences in the wine industry.
  • Undergraduate students have embarked on undergraduate research experiences pertaining to wine research within the College of Agricultural Sciences. Several of these projects have benefited the local wine industry.
  • Graduates from Food Science have started to “harvest hop” to the southern hemisphere for winemaking and production experiences internationally. Virginia (Smith) Mitchell, head winemaker at Galer Estate Winery, traveled to Australia in the winter months of 2013 while Allie Miller will travel to New Zealand for the 2016 harvest.  These experiences bring a global perspective and education that facilitate innovative changes to the growing Pennsylvania wine industry.
  • Several students have benefited from permanent placement in the wine and fermented beverage industries upon graduation, and many have committed to Pennsylvania operations. The experience gained through research winemaking here at Penn State is invaluable and leaves them with base knowledge in wine production.
  • Many students volunteer for Extension programming, which gives them the opportunity to present research and educational experiences to industry members as well as network with potential employers (you!).
  • Graduate research has flourished. Both Dr. Ryan Elias and Dr. Michela Centinari have several graduate students that are working on applied research projects which address winemaker and grower needs reflected in previous industry needs assessments.
  • Since 2011, the number of research wines being made has more than quadrupled. Today, we have outgrown the equipment I used in 2011 and outgrown our storage capacity for research wines.  The wines produced at Penn State are annually evaluated at regional Extension events.

With such a positive focus on student development and interaction with Pennsylvania’s grape and wine industry, the 2015 vintage was expected to be our best vintage yet!

The 2015 growing season did not leave much hope for Pennsylvania grape growers and winemakers, and I can recall a series of summer meetings in which winemakers from across the state asked me if I was prepared to deal with a lack of fruit and a bunch of rot in our research winemaking curriculum.  Luckily, as Michela will reflect upon next week, the season shaped up to be one of the best I have experienced in my time here at Penn State.

For 2015, we recruited 10 interested undergraduate students for the 2015 harvest season to assist with the research harvests and wine production.   This is double the quantity of students that typically enroll in an independent study experience associated with enology.

Students participate in regular wine processing operations, which can be seen in Figures 2 – 7: crushing, pressing, monitoring fermentation, and completing wines through malolactic fermentation.  Additionally, at the end of the semester, each enrolled student presents on a wine grape variety of interest.

Many students arrive with a genuine interest in fermentation science, or would like to get more experience in food production.  Many of them leave the fall semester with future undergraduate research opportunities, internships/co-ops at wineries, or develop an expectation to graduate with permanent placement in the fermented beverage industry.

Figure 2: The undergraduate students start each fall with a review of lab analysis techniques to learn how to properly analyze juice and wine, which comes in handy during the harvest season.  Photo by: Denise M. Gardner

Figure 2: The undergraduate students start each fall with a review of lab analysis techniques to learn how to properly analyze juice and wine, which comes in handy during the harvest season. Photo by: Denise M. Gardner

Figure 3: Crush is an essential part of the independent study class and graduate student research.  Careful care is taken by the students to ensure that proper sanitation is taken, accurate yields are measured, and that treatments are adequately separated into replicate fermentations. Photos by: Denise M. Gardner

Figure 3: Crush is an essential part of the independent study class and graduate student research. Care is taken by the students to ensure that proper sanitation is utilized, accurate yields are measured, and that treatments are adequately separated into replicate fermentations. Photos by: Denise M. Gardner

Figure 4: Prepping inoculums for primary and malolactic fermentations is an important part of what the students learn how to do throughout the semester.  Here, Blair and Cara prep hydration nutrient and yeasts for inoculations. Photo by: Denise M. Gardner

Figure 4: Prepping inoculums for primary and malolactic fermentations is an important part of what the students learn how to do throughout the semester. Here, Blair and Cara prep hydration nutrient and yeasts for inoculations. Photo by: Denise M. Gardner

Figure 5: Students also learn how to properly inoculate wines for primary fermentation.  A: Marielle, Stephanie, Joe, Garrett, Gary and Blair inoculate Riesling wines; Photo by: Denise M. Gardner; B: Denise and Gary inoculate Cabernet Sauvignon musts; Photo by: Marlena Sheridan.

Figure 5: Students also learn how to properly inoculate wines for primary fermentation. A: Marielle, Stephanie, Joe, Garrett, Gary and Blair inoculate Riesling wines; Photo by: Denise M. Gardner; B: Denise and Gary inoculate Cabernet Sauvignon musts; Photo by: Marlena Sheridan.

Figure 6: Racking techniques without a pump. [From left to right] Liv, Maria, and Marielle rack Riesling juice into replicate fermentation carboys.  Photo by: Denise M. Gardner

Figure 6: Racking techniques without a pump. [From left to right] Liv, Maria, and Marielle rack Riesling juice into replicate fermentation carboys. Photo by: Denise M. Gardner

Figure 7: Pressing [white/rosé] juice or finished [red] wine is always an experience. A: Gary, George, and Garrett press rosé to prepare for overnight settling, B: Stephanie loads the press with crushed white berries, C: Allie fills a carboy of finished red wine, D: Laura, Marlena, Gary, Garrett, and Blair preparing for red wine pressing, and E: Marielle sits in the splash zone for red wine pressing.  Photos by: Denise M. Gardner

Figure 7: Pressing [white/rosé] juice or finished [red] wine is always an experience. A: Gary, George, and Garrett press rosé to prepare for overnight settling, B: Stephanie loads the press with crushed white berries, C: Allie fills a carboy of finished red wine, D: Laura, Marlena, Gary, Garrett, and Blair preparing for red wine pressing, and E: Marielle sits in the splash zone for red wine pressing. Photos by: Denise M. Gardner

I can’t wait to share some of the 2015 wines with the local industry at the March 2016 PA Wine Marketing & Research Board Symposium or at future Extension Enology events.

As a general reminder, many of these projects are financially supported through the multi-state Grape Wine Quality Eastern U.S. Initiative SCRI grant (which partially funds the NE-1020 variety trial research program), the PA Wine Marketing and Research Board, and the Crouch Fellowship, among other grant agencies.

Here are just a few snap shots that depict everything that we are currently working on for the 2015 harvest season:

Figure 8: This year’s NE-1020 variety trial projects include yeast trials, an evaluation of tartaric acid additions to red wine varieties grown in high potassium vineyard sites (A), and pre-fermentation juice treatments in Vidal Blanc wines (B).  Photos by: Denise M. Gardner

Figure 8: This year’s NE-1020 variety trial projects include yeast trials, an evaluation of tartaric acid additions to red wine varieties grown in high potassium vineyard sites (A), and pre-fermentation juice treatments in Vidal Blanc wines (B). Photos by: Denise M. Gardner

Figure 9:  The Crouch Fellowship currently supports a project pertaining to the impact of spray-on frost protection products on grape and wine quality.  A: Graduate student, Maria Smith, gets ready for a full day of processing after a full day of harvest. B: Marielle and Cara monitor the red wine fermentations through daily punch downs, temperature logs, and Brix measurements.  Photos by: Denise M. Gardner

Figure 9: The Crouch Fellowship currently supports a project pertaining to the impact of spray-on frost protection products on grape and wine quality. A: Graduate student, Maria Smith, gets ready for a full day of processing after a full day of harvest. B: Marielle and Cara monitor the red wine fermentations through daily punch downs, temperature logs, and Brix measurements. Photos by: Denise M. Gardner

Figure 10: Graduate student, Marlena Sheridan, takes a photo of a cluster representation for her research project on red wine color stability. Photo by: Denise M. Gardner

Figure 10: Graduate student, Marlena Sheridan, takes a photo of a cluster representation for her research project on red wine color stability. Photo by: Denise M. Gardner

Figure 11: Graduate student, Laura Homich, enjoys time in the Noiret vineyard for her research project that focuses on the effect of canopy management practices on rotundone (black pepper flavor) development in Noiret grapes and wine.

Figure 11: Graduate student, Laura Homich, enjoys time in the Noiret vineyard collecting berry samples for her research project that focuses on the effect of canopy management practices on rotundone (black pepper flavor) development in Noiret grapes and wine. Photo by: Maria Smith

Figure 12: Graduate student, Gal Kreitman, prepares inoculates on Vidal Blanc in relation to a project on the influence of copper on thiol-containing aroma/flavor compounds. Photo by: Denise M. Gardner

Figure 12: Graduate student, Gal Kreitman, prepares inoculates on Vidal Blanc in relation to a project on the influence of copper on thiol-containing aroma/flavor compounds. Photo by: Denise M. Gardner

Figure 13: Another full year of research winemaking at Penn State – vintage 2015.  Photo by: Denise M. Gardner

Figure 13: Another full year of research winemaking at Penn State – vintage 2015. Photo by: Denise M. Gardner

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