By Molly Kelly
There are a number of spoilage microorganisms and yeasts that we are concerned with as winemakers. Two of the most common spoilage yeasts include Kloeckera apiculata and Brettanomyces bruxellensis. The most common form of yeast spoilage is due to Brettanomyces bruxellensis. Although mature grapes may harbor this spoilage yeast, the bigger problem can occur when winery equipment is infected due to poor sanitation practices. This yeast produces volatile phenols and acetic acid. Examples of wine flaws include aromas described as “medicinal” in white wines and “leather” or “horse sweat” in red wines. Other aromas descriptors include barnyard, wet dog, tar, tobacco, creosote, plastic and band aids.
The two major groups of wine spoilage bacteria can be placed in either the acetic acid bacteria (AAB) group or the lactic acid bacteria (LAB) group. The AAB includes the genera Acetobacter and Gluconobacter. Both have aerobic (requiring oxygen) metabolisms and thus their growth generally occurs on wine surfaces as a translucent film that tends to separate into a patchy appearance. In contrast, the LAB require low oxygen conditions for growth (i.e. they are microaerophilic to facultative anaerobic micro-organisms). The LAB includes the genera Lactobacillus, Pediococcus and Oenococcus.
During fermentation the presence of such microbes may be indicated by a spontaneous or sluggish fermentation, or a spontaneous malolactic fermentation (MLF); or the presence of ethyl acetate, volatile acidity (VA) or other off-odors.
Winery Microbiology Laboratory
Because of these possible faults arising due to the presence of spoilage organisms, some wineries have incorporated sanitation monitoring and microbiological techniques into their production practices. Some considerations when planning a winery microbiology laboratory are: space considerations, availability of trained staff to perform testing, willingness to maintain adequate record-keeping, equipment costs as well as the cost of consumables.
A microscope capable of 1000x magnification is needed to view bacteria and yeast. These can cost anywhere from $1000-$3000 or more but bargains can be found on used microscopes. A phase-contrast microscope requires no staining of slides due to enhanced differences in refractive index between the microorganisms and surrounding medium. This feature also allows for rapid detection and response. The staff in the microbiology lab should have training in the proper use of a microscope as well as identification of microorganisms.
In addition to identifying spoilage organisms, a microscope can be used to monitor yeast populations. By using a simple methylene blue stain, yeast viability can be determined.
Bacterial culture media is available for the growth of spoilage organisms for identification. This requires additional equipment including an incubator. This also requires further training in sterile technique and organism identification techniques. Several types of culture media exist for the detection of the organism of interest. For example, media used to plate for Brettanomyces contains chloramphenicol (200 mg/L) to prevent bacterial growth while others may contain cyclohexamide to prevent Saccharomyces growth. Common media used in culturing juice, wine and environmental samples include WL and WL-differential agar.
Membrane Filter Method
The membrane filter method can be used to isolate small numbers of microbes from a liquid sample. A sterile cellulose nitrate membrane (0.45 microns for bacteria, 0.65-8 microns for yeasts) is placed on a vacuum flask and filtered. Using sterile technique, the membrane is placed on the culture plate and monitored for growth. This method could be used to check bottle sterility.
The swab test method is used for semi-quantitative analysis. Moist sterile cotton swabs are used to monitor dry areas (moistened with sterile saline or water). Dry swabs can be used to test moist areas. The swabs can then be used to inoculate the proper agar medium, depending on the organism of interest. Agar plates can also be used to detect airborne organisms at critical winery locations. Plates are left open for 30 minutes to 2 hours and then incubated. Airborne organisms that settle on the plate will grow and can be further identified.
Monitoring systems exist that utilize bioluminescence technology to measure adenosine triphosphate (ATP). ATP is found in all plant, animal and microbial cells and is the prime energy currency that fuels metabolic processes. It is therefore possible to detect and measure biological matter that should not be present if proper sanitation practices are followed. One system by Hygiena™ uses an enzyme found in fireflies (luciferase). In the presence of ATP, an oxidation reaction occurs that results in light formation that is directly proportional to the amount of ATP present. Results are numeric and expressed as relative light units (RLU).
It should be stressed that cellar hygiene is critical in maintaining wine integrity and quality. Poor wine quality is usually due to poor sanitation practices. Areas of spoilage organism build-up include: the vineyard, second-hand barrels, imported bulk wine and areas of the winery that are difficult to reach.
There are commercial enology laboratories that provide all of the microbiological services discussed here. For more information please contact Molly Kelly at firstname.lastname@example.org.
Crowe, A. August 2007. Avoiding Stuck Ferments. Wine Business Monthly
Just, E. and H. Regnery. 2008. Microbiology and wine preventive care and monitoring in the wine industry. Sartorius Stedim Biotech.
Margalit, Y. 1996. Winery Technology and Operations. The Wine Appreciation Guild, San Francisco.
Ritchie, G. 2006. Stuck Fermentations. Fundamentals of Wine Chemistry and Microbiology. Napa Valley College.
Specht, G. Sept/Oct 2003. Overcoming Stuck and Sluggish Fermentations. Practical Winery and Vineyard Journal.
Van de Water, L. Sept/Oct 2009. Monitoring microbes during fermentation. Practical Winery and Vineyard Journal.
Zoecklein, B., Fugelsang, K.C., Gump, B.H. and Nury, F.S. 1999. Wine Analysis and Production, Kluwer Academic/Plenum Publishers, New York.
Zoecklein, B. 2002. Enology Notes #65, Enology-Grape Chemistry Group, Virginia Tech.
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.
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 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 (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,
- periodically through storage (e.g., every 2-3 months) and
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.
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.
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).
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
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.
Still Worried About Your Wine Post-Bottling?
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:
- An Overview of Winery Sanitation by Patricia Howe: https://www.umpqua.edu/images/areas-of-study/career-technical/viticulture-enology/downloads/conferences/technical-symposia/2011-march-wine-flaws/2011-ts-howe-winery-sanitation.pdf
- Making Cleaning and Sanitation Practical for the Small Commercial Winery by Denise M. Gardner: http://bit.ly/PracticalWinerySanitation
- Minimizing Spoilage of Wines in Barrel by Denise M. Gardner: http://bit.ly/WineBarrelSanitation
- Bottling Line Cleaning Protocol by Scott Labs: http://www.scottlab.com/uploads/documents/technical-documents/1191/Bottling%20Line%20Cleaning%20Protocol.pdf
- Preparing Wines for Bottling by Enartis Vinquiry: http://www.enartis.com/upload/images/03_2016/160311011309.pdf
- Starting a Lab in a Small Commercial Winery: http://extension.psu.edu/food/enology/analytical-services/setting-up-your-winerys-lab
- Wine Analytical Labs: How Your Winery Can Use Them: http://extension.psu.edu/food/enology/analytical-services/wine-analytical-labs-how-your-winery-can-use-them
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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!
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.
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.
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.
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
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
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.
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:
- Wet Dog
- Plastic or Burnt Plastic
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.
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.