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Harvest Preparation for Sub-Optimal Fruit: Botrytis

By: Denise M. Gardner

The eastern U.S. growing seasons can be somewhat unpredictable.  Late season rains or untimely hurricane events can be a recipe for disaster for local grape growers (http://www.pawinegrape.com/uploads/PDF%20files/Documents/Viticulture/Harvest/Rain%20at%20Harvest.pdf), and a few have been unprepared for such events in the past.  These weather events can lead to higher incidences of the grey-rot form of Botrytis in addition to other rots, which may also be related to pest damage.  Furthermore, these weather incidences and pest damage can ultimately impact picking decisions for growers and wineries (Osborne, 2017).

It is almost inevitable that wineries need to be prepared for end-of-season weather flops, and plan for the best possible ways to manage or maintain wine quality in light of above-average disease pressure.

One disease that winemakers can prepare for prior to harvest is Botrytis.  For the purpose of this article, we’ll be using the term Botrytis to indicate the grey-mold or grey-rot form of the disease.  Grey-mold, the form of Botrytis more commonly noticed in humid regions or during heavy-precipitation seasons, can ultimately affect wine quality.  Peynaud (1984) has defined 4 ways in which the grey-mold can negatively affect wine quality:

  • Deplete wine color (especially important in red varieties),
  • Increase the risk of premature browning (through oxidative enzymes),
  • Deplete varietal character (through degradation of grape skins), and
  • Contribution to off-flavors developed by the mold’s presence on the fruit.

Botrytis, grey-mold, infection can force winemakers into alternative winemaking techniques in order to retain wine quality. Photo by: Denise M. Gardner

Based on a 1977 study by Loinger et al., guidelines pertaining to wine quality were developed with regards to a visual assessment of Botrytis incidence on incoming fruit:

  • 5-10% Botrytis rot on clusters: noticeable reduction in wine quality; wine quality is still “good” (as opposed to very good with 0% rot on clusters)
  • 20-40% Botrytis rot on clusters: marked reduction in wine quality; wine quality is “low”
  • >80% Botrytis rot on clusters: wine is commercially unacceptable

With a noticeable sensory and chemical difference in Botrytis-infected clusters, it is best for wineries to develop a standard operating procedure (SOP) for assessing rot-infected fruit, as well as how the grapes should be handled and processed during production.  While there is no one correct way to work with the wine, below are some suggestions or options that wineries can integrate when dealing with Botrytis-infected grapes.  For a full list of possibilities, please visit: http://extension.psu.edu/food/enology/wine-production/producing-wine-with-sub-optimal-fruit/fermenting-with-botrytis-101

Pre-Fermentation Sorting

Some wineries will sort through all incoming grape clusters prior to the crushing/destemming process to assess for any cluster damage or presence of unwanted material.  If your operation is not set up with this equipment, sorting can also take place in the vineyard.  Depending on the concentration of disease and on the projected wine style or quality parameter the fruit will go towards, disease portions of clusters can be cut out in the vineyard.  Or diseased fruit can be left in the vineyard to deal with after the harvest is complete.  Sorting out diseased fruit from that of decent quality will reduce the impact of the mold on the wine’s aroma, flavor, and quality.

Limit Contact Time with Skins

Depending on the resource, there are various recommendations for how to handle diseased fruit.  In whites, some recommend whole cluster pressing and tossing the first 10+ gallons, which are rich in Botrytis metabolites (Fugelsang and Edwards, 2007).  Many recommend separating juice press fractions for white and rosé wines, as this will give the vintner more control over the chemical constituents (e.g., phenolics, enzymes, and disease-related off-flavors) in the final wine.

Depending on the desired outcome for a red wine, treating or limiting skin contact with diseased fruit may be ideal post -primary fermentation.  This would include avoiding extended maceration processes.  Due to the fact that the presence of Botrytis on red varieties reduces anthocyanin and phenolic extraction (Razungles, 2010) in addition to the varietal aromatics, excessive skin contact may not be ideal during primary fermentation.  Whole berry fermentations, as opposed to a more aggressive crush and destem process, may help minimize extraction of Botrytis metabolites, which can also contribute to mouthfeel variations or off-flavors.

Tannin additions pre-fermentation may also be good considerations to compensate for phenolic losses associated with Botrytis infection.  Pre-fermentation and post-fermentation additions may help rebuild the wine’s structure or provide constituents for color stabilization.

Flash pasteurization (i.e., flash détente) has been previously recommended for Botrysized fruit to inactive the laccase enzyme associated with Botrytis, enhance color stability in reds, as well as improve the aromatics and flavors associated with the final wine.  Wines that undergo a thermovinification step tend to extract more anthocyanins and phenolics compared to traditionally fermented wines (Razungles, 2010).  Additionally, this heat step helps to inactivate laccase, which can contribute to early browning or oxidation of young wines.  However, commercial producers may not find this technological application easily accessible.

Therefore, in addition to minimizing skin contact time, winemakers will want to reduce contact time with the gross lees, and may also remove the wine from fine lees associated with the mold-infected fruit quickly.  The integration and use of clean, fresh lees, however, is still encouraged.  Removing the lees associated with mold-infected fruit can help reduce additional contact time with rot metabolites that have settled out with the lees.  This inhibits further integration of those metabolites into the wine.

Inoculate with a Commercial Yeast Strain

The presence of rot is one incidence in which processing techniques (e.g., cold soak) that encourage native microflora to dominate the fermentation are probably not desired.  Things like cold soak and native ferments allow ample opportunity for the mold to progress and contribute to the wine’s flavor.

Fruit that has rot or microflora issues is best inoculated with commercial yeast and malolactic bacteria strains to outcompete the native microflora (including those microorganisms that contribute to the rot), and to give the fermentation its best chance at completing the fermentation cleanly.  Remember that proper yeast nutrition is important to support the yeasts’ growth and to reduce the risk of hydrogen sulfide development.  For more information on determining the starting nitrogen concentrations (YAN) and how to properly treat your fermentation with added nutrients, please refer to:

Penn State Extension’s Wine Made Easy Fact Sheet: Nutrient Management During Fermentation

With high Botrytis concentrations, a more robust yeast strain may be preferred in order to quickly get through primary fermentation.  A quicker fermentation may simplify the aromatics associated with the wine, but it will also ensure little opportunity for additional spoilage.  Saccharomyces bayanus strains are often selected as more robust yeast strains.

Use of commercial yeast strains can be a valuable tool when dealing with disease-infected fruit. Photo by: Denise M. Gardner

Use of Sulfur Dioxide

Sulfur dioxide additions at crush will be determined based on the style of wine in which you are producing (e.g., white, rosé, red, etc.), but in general, the use of sulfur dioxide can help inhibit further spoilage of your product and retain antioxidant capacity.  Sulfur dioxide additions in the juice stage will help minimize early browning, but primarily inactivate PPO.

In general, botrysized wines tend to require more sulfur dioxide as Botrytis metabolites bind with free sulfur dioxide (Goode, 2014).  This is true even when processing wines with the noble rot version of Botrytis.

When primary fermentation, and malolactic fermentation (dependent on style), is complete it is a good idea to ensure that the wine has an adequate free sulfur dioxide content in order to retain its antimicrobial protection.

Fining

Some fining agents may also be applicable in the juice stage.  For example, some producers find it helpful to fine juice with bentonite in order to reduce protein content, as well as help minimize rot-associated off-flavors or partially reduce laccase concentrations.

PVPP can be added to the juice to reduce potential browning pigments or their precursor forms (Van de Water, 1985).

In both of these scenarios, neither bentonite or PVPP is specific for rot-related constituents, but each could be helpful to avoid potential challenges later on in the production process.

The presence of Botrytis can also contribute glucans to the must/wine, which can cause filterability problems for heavily-infected wines.  In this situation, many suppliers have beta-glucanase enzymes that can be applied either to the juice, wine, or both, to help breakdown the glucans and enhance ease of filterability.

A Word about Laccase

Both polyphenol oxidase (PPO) and laccase can cause early browning in grapes and wine.  However, PPO is inhibited by the alcohol content that is developed during primary fermentation.  Laccase, however, is not inhibited by the presence of alcohol, and can only be inactivated by a pasteurization step, heated to at least 60°C (140°F) (Wilker, 2010).

Grapes tend to be higher in laccase concentration when infected with Botrytis, and, thus, wines produced from grapes that had a high incidence rate of Botrytis can develop a brown hue post-primary fermentation.  This oxidative activity can occur even in young wines.

If you are concerned about the prevalence of laccase in diseased-fruit, wineries can submit wine samples to a wine lab for a laccase test.  Or, if you own a copy of “Monitoring the Winemaking Process from Grapes to Wine: Techniques and Concepts” by Patrick Iland et al., pg. 90 and 94 have 2 laccase test protocols that outline how wineries can assess oxidation by laccase.  The results of these test will indicate if extreme treatments are required during production to avoid the rapid and early oxidation caused by laccase.

 

Additional Resources:

 

Literature Cited:

Goode, J. 2014. The Science of Wine: From Vine to Glass. (2nd Ed.) University of California Press: Berkley, California. 216 pg.

Fugelsang, K.C. and C.G. Edwards. 2007. Wine Microbiology: Practical Applications and Proceedings. (2nd Ed.) Springer: New York, NY. 393 pg.

Loinger, C., S. Cohen, N. Dror, and M.J. Berlinger. 1977. Effect of grape cluster rot on wine quality. AJEV. 28(4): 196-199.

Peynaud, E. 1984. Knowing and Making Wine. Wiley-Interscience: New York, NY. 391 pg.

Razungles, A. 2010. Extraction technologies and wine quality. In Managing Wine Quality, Vol. 2 Oenology and Wine Quality. Andrew G. Reynolds, Ed. Woodhead Publishing: Philadelphia, PA. 651 pg.

Van de Water, L. 1985. Fining Agents for Use in Wine. The Wine Lab.

Wilker, K.L. 2010. How should I treat a must from white grapes containing laccase? In Winemaking Problems Solved. CRC Press: Boca Raton, Florida. 398 pg.

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Further Pre-Harvest Cellar Preparations to Consider

By: Denise M. Gardner

Last week, we reviewed scheduling bottling operations and pre-ordering harvest supplies in the month of July in order to open up space in the cellar and save financial resources on free-shipping promotions, respectively: July Pre-Harvest Planning in the Cellar

This week, we’ll review a few extra considerations as the cellar prepares for the up-coming harvest season.

What wine components will you measure in grapes/juice?

At minimum, each incoming lot of grapes or juice should be analyzed for:

  • Brix,
  • pH,
  • titratable acidity (TA), and
  • yeast assimilable nitrogen (YAN).

For grapes and juice, refractometers are quick tools that can provide a quick reference for the sugar concentration of grapes and juice.  Once primary fermentation is underway, it is best to switch to hydrometers to measure the drop in sugar concentration, as alcohol can interfere with sugar concentration readings when using a refractometer.

Using a hydrometer to monitor primary fermentation is preferred over the use of a refractometer due to the fact alcohol content interferes with a refractometer’s readings. Photo by: Denise M. Gardner

The pre-harvest time period is a good time to ensure that pH meters and all titration supplies are working properly.  Ensure the pH electrode is working properly and that there are plenty of [fresh] calibration standards and buffers to sustain the production through harvest.  For titrations, it is a good idea to replenish sodium hydroxide.

YAN analysis can be accomplished enzymatically or by Formol titration.  Both come with challenges and require some experience and expertise to run efficiently and effectively.  With enzymatic analysis, new enzyme kits are typically required for the current year’s harvest.  Purchasing these kits right before harvest could be a time saver for when fruit arrives. For more information on YAN analysis, please refer to:

Having protocols for each analysis that will be run in-house ready for incoming lab assistants or harvest interns can also save time and energy during the harvest season.

Check chemical expiration dates and re-order supplies where needed.  In July, some suppliers may offer discounts or promotions, like free shipping.

If the winery is able to run analyses like free/total sulfur dioxide by aeration oxidation, volatile acidity by cash still, or Rippers, it may be imperative to update chemicals for the up-and-coming harvest season.  Chemicals like hydrogen peroxide (H2O2) and Iodine have a limited shelf-life that will not be reliable if purchased the previous year.

If the winery is using a microscope, make sure that the microscope is working properly and not in need of any repairs.  Update the lab’s record books with images of relevant microorganisms that may help lab personnel better identify any problem microflora in juice or wine.  The use of a microscope can be a great tool to assess the quality of incoming fruit or help determine problematic fermentations.

For wineries that distribute samples to certified laboratories, stock up on sample bottles and any supplies that you would need to take representative samples during the harvest season.  Some labs will pre-distribute sample bottles to the winery free of charge.

Stock up on sample bottles before harvest begins to efficiently collect required juice/wine samples that will be shipped to a laboratory. Photo by: Denise M. Gardner

Bring Quality Control Standard Operating Procedures (SOPs) Up-to-Date

Standard Operating Procedures (SOPs) are step-by-step plans that detail a winery’s production steps and/or lab analyses.  The development and integration of SOPs can be time consuming, especially considering it can be challenging to effectively document a winemaker’s communications on production steps.  However, wineries can build SOP policies over time, especially during moments of downtime in the cellar.

The evaluation of production-based prior to harvest can ensure that all employees are aware of production decisions, proper safety practices, and preparation steps for harvest.  Properly trained employees prior to the onset of harvest guarantee a smoother work-flow system and lays out production expectations before crunch time.

For wineries that run analysis in-house, SOPs or protocols can be developed for each analysis and general laboratory practices.  If you need a reference for lab protocols, Enartis USA (Vinquiry) provides a series of examples: http://www.enartis.com/us/tools/wine-analysis

Going through laboratory SOPs with employees prior to harvest can help guarantee training for all employees whose primary focus will be in the lab during harvest.  This may save time and effort during the harvest season when it may not be possible for upper management to train other employees.

When an SOP notebook or database has been developed, each employee should be aware of the SOPs, how to access them, their purpose, and have a general idea on what they include to ensure that production runs smoothly year round.

Visiting the Vineyard

If the winery is contracted with growers, it is a good idea to form an established, working relationship with the growers.  Now is the time, before harvest, to have regular vineyard walk-throughs, evaluate the fruit, and discuss harvest expectations for incoming fruit.  Talk about ripening expectations and taste the berries with growers so that they get a good sense for the sensory evaluation of the fruit.

Berry sensory analysis developed by the L’Institut Coopertif du Vin (ICV) in France can be a powerful learning tool for both growers and vintners, and could be a consideration for commercial wineries.

Additional Resources

“Harvest Preparation” by Dr. Muli Dharmadhikari http://www.extension.iastate.edu/NR/rdonlyres/173729E4-C734-486A-AD16-778678B3E1CF/73932/HarvestPreparation.pdf

“Monitoring the winemaking process from grapes to wine: techniques and concepts” by Patrick Iland, Nick Bruer, Andrew Ewart, Andrew Markides, and John Sitters.  ISBN: 978-0-9581605-6-8

“Winemaking Problems Solved,” Edited by Christian E. Butzke.  ISBN: 978-1-4398-3416-9

Lab Analysis Protocols by Enartis USA: http://www.enartis.com/us/tools/wine-analysis

July Pre-Harvest Planning in the Cellar

By: Denise M. Gardner

If you are a wine producer in the northern hemisphere, harvest may feel quite far away.  However, given that it is now the month of July, it will be here before we all know it.

Harvest season is just around the corner! Photo by: Denise M. Gardner

The month of July is a great time to start preparing a few essential pre-harvest tasks including getting a bottling schedule ready, especially if bottling operations have not yet begun, and ordering harvest supplies.   This blog post will focus on these two tasks.

Prepare and Enact a Bottling Schedule

New grapes are about to flood your winery with juice and future wine.  Now is the time to review inventory within the cellar and determine what has to be moved and what has to be bottled before harvest begins.

Freeing up previous years’ inventory by moving it into bottle will free up tank, barrel and storage space for this year’s incoming fruit.  It makes for a much easier transition if all of the wines that need bottling are bottled before harvest season starts.  Bottling during harvest is not only chaotic, but it tires employees, pulls resources from the incoming product, and may lead to harvest decisions that may be regretted later.

Always make sure to get bottled wines properly stored and away from any “wet areas” on the production floor.  If possible, bottled wines should have a separated storage area within an ideal environment that is physically separated from production.  From there, stored wines can be moved into retail space when needed.

For more information on how to get wines prepared for bottling, please visit our previous posts:

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

Ordering Fermentation and Lab Supplies

Many suppliers and wine labs offer free shipping in July, which can especially be useful for wineries that are not geographically close to a winery supply store-front.  Planning ahead and determining what fermentation supplies will be needed in August, could save extra money.  Not to mention, having supplies on hand during the busy processing season can be a big stress relief.

Winemakers should also take the time to look at new fermentation products and assess the previous year’s needs in order to adequately supply for the up-and-coming harvest.  Keeping an annual inventory of purchases can be helpful to isolate regular needs.

Things to consider purchasing include:

  • Yeast
  • Fermentation Nutrients
  • Malolactic Bacteria
  • Enzymes
  • Yeast Hulls
  • Salts for Acid Adjustments
  • Tannins
  • Pectic Gums and/or Inactivated Yeast Products
  • Fining Agents
  • Oak Alternatives or Barrels
  • Sanitizing Agents

While new yeasts are released frequently, being constructive about the production’s fermentation needs can help isolate what yeasts are needed for the upcoming harvest.  I typically recommend that all vintners have at least 5 strains on hand for harvest: 2 reliable strains that will get through primary fermentation with little hassle, 1 strain that can be relied upon for sluggish or stuck fermentations, and 2 strains for specialty needs (e.g., sparkling or fruit wine/hard cider production) or experimental use.

Select and purchase your yeast strains in July to take advantage of free-shipping promotions. Photo by: Denise M. Gardner

Fermentation nutrients should be a must-have for all wineries to help minimize the risk of hydrogen sulfide.  Always double check nutrient requirements for yeast strains purchased.  In general, wineries will need hydration nutrients (e.g., GoFerm), complex nutrients (e.g., Fermaid K), and diammonium phosphate (DAP).

For more information on why YAN is important and how yeasts utilize nitrogen during primary fermentation, please visit the following blog posts:

If you need further step-by-step instructions on how to determine adequate nutrient additions during primary fermentation, please visit our Penn State Extension fact sheet: Wine Made Easy Nutrient Management during Fermentation

Sometimes hydrogen sulfide will arise in a wine by the time primary fermentation ends despite all preventative care.  Making sure there are adequate supplies on hand, such as copper sulfate and PVI/PVP can save time in the future.  Also make plans for ways that the production can reserve fresh lees.  PVI/PVP is a fining agent that can help reduce metals like residual copper, but fresh lees will also help reduce the perception of hydrogen sulfide aroma/flavor and residual copper in the wine.  Having a plan for retaining and storing lees during harvest season can save time during challenging situations that develop through the end of harvest and into the winter’s storage season.  A fact sheet on copper screens and addition trials can be found at the Penn State Extension fact sheet: Wine Made Easy Sulfur-Based Off-Odors in Wine.

I also like to make sure we have supplies on hand in case of heavy disease pressure come harvest.  This includes things like Lysozyme, beta-gluconase, pectinase or other clarification enzymes, and fermentation tannins.  Lysozyme can help reduce lactic acid bacteria levels while beta-gluconase can assist clarification problems associated with Botrysized wines.  For further information on how to manage high-disease pressured fruit, please visit the Penn State Extension website on Fermenting with Botrytis or Managing Sour Rot in the Cellar.

Double check the storage requirements for all materials purchased before and after the product is opened.   It’s important to store all of those supplies in the winery properly as it will ensure their efficacy by the time the product is needed.

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:

 

Haskap -A New Kind of Wine

By: Jody Timer, Entomology at LERGR & EC

In the colder parts of this state, we are always looking for new berries to make into wine.

Ideally, we are on a search to find berries that will stand cold winters and late frosts.  As an end to this means, three years ago at Lake Erie Regional Grape Research and Extension Center (LERGR & EC) we planted an experimental patch of Haskap bushes (Lonicera caerulea).

Haskap (Blue Honeysuckle) Berries. Photo from: Haskapa.com

Haskap or blue honeysuckle, is an extremely cold hardy, edible berry producing plant, resisting temperatures as low as -46°C (-50.8°F) (Thompson 2008). Even flowers can be exposed to temperatures of -7°C (19.4°F) with no detriment to fruit set. Haskap is also tolerant of a wide range of soil pH (5.5-7.5) (Retamales and Hancock 2012) allowing for production in many different soils. The bushes will survive in the wild in swamp-like conditions, but they thrive in well drained soils. The fruit development period for Haskap starts very early in spring and is very short; 6-8 weeks from bloom to harvest (Thompson 2006). In our climate, Haskap will produce fruit as early as mid-June, coinciding somewhat with the strawberry market. The small blue fruits have a fresh, somewhat tart, raspberry/blueberry to cranberry flavor. They should be purple all the way through before they are fully ripe. These plants do not sucker, need little pruning, and tend to fruit when very young. A Haskap bush can be productive for 30 years. Haskaps are native to Siberia and northeastern Asia (Bors et al. 2012), and were recently introduced to the North American market being advertised for its many claimed health benefits. Some researchers (Bors et al. 2012) believe that haskap could replace blueberries as the new ‘super fruit’. Lonicera have been used widely in folk medicine in northern Russia, China and Japan since ancient times. In recent years, phenolic compounds present in fruit crops, especially berries, have gained much attention due to the accumulating scientific evidence of their potential health benefits. Its juice has 10 to 15 times more concentrated color than cranberry juice. The fruit is high in Vitamin C, Vitamin A, fiber, and potassium.

Antioxidant levels are measured using the ORAC (oxygen radical absorbance capacity) method. A wide variety of food has been tested using this methodology, with the Haskap Berry being rated very highly in comparison with other berries. The berries’ extremely high ORAC value indicates a high anthocyanin, poly phenol, and bioflavonoid content.

In addition to fresh market potential, Haskap can be used in processed products including pastries, jams, juice, ice cream, yogurt, sauces, and candies. These berries also make a nice dark red or burgundy colored wine. The Canadian market is receives about $13.00 per pound, while the Japanese market is about $30.00 per pound of berries (LaHave Forests’ Haskap Day).

Haskap fruits obtain almost full size 4 weeks after blooming and begin to turn purple. The dark skin of the fruit is covered by a waxy coating (bloom) and resembles the outer covering of blueberries and concord grapes. At 5 weeks old they are fully purple but at 6 or 7 weeks old they are fully ripe and tasty. That is for a normal year. But some varieties do develop slower especially if not pruned to let in enough light. Though Haskap is touted as having few disease and insect pest problems, the plant can be negatively impacted by sunburn, mildew and birds.

Haskap Bushes. Photo from aumacksimertals.com

Haskap Bushes. Photo from: honeyberryusa.com

Bob Bors of University of Saskatchewan has been the primary researcher of Haskap varieties. The following is from the research at the University of Saskatchewan (www.usask.ca/agriculture/dom_fruit/index.html):

Like many other fruit crops, haskap requires pollen from an unrelated variety in order to set fruit. Haskap does not have separate male and female plants. When two compatible haskap varieties are planted close to each other, both bushes will set fruit. But it is not enough to have compatible pollen. To pollinate each other both plants must bloom at the same time and be genetically compatible. There is overlap between nearby groups but peak bloom is usually five days different between categories.  Blooming times are dependent on where the Haskap are located. 

‘Tundra’ may be the variety best suited for commercial production at this time (2007).Tundra’s fruits were firm enough to withstand commercial harvesting and sorting at the University of Saskatchewan, yet tender enough to melt in the mouth. Firmness is a rather rare trait especially for large fruited blue honeysuckles. Ranking at almost the top for flavor and fruit size the shape of its fruit was deemed acceptable for the Japanese market. Its fruit is at least 50% larger than blue honeysuckles currently available in Canada and the US. Its firmness and the fact that this variety does not ‘bleed’ from the stem end when picked could make this variety especially suited for Individually Quick Frozen (IQF) processing.

‘Borealis’ has the distinction of having the best testing and largest fruit size in our breeding program as of 2007. (However, there were many good tasting haskap varieties and it was hard to decide) Its fruits were usually twice the size of any of the 35 Russian varieties in our collection of similar age. (Most varieties of haskap/blue honeysuckles seem to have larger fruit as the bushes get older). Unfortunately, this variety does not have the firmness of ‘Tundra’ and it is not suitable for IQF. It tends to get a bit mushy when handled with equipment. It may be best for home gardeners or U-pick operations who can hand pick the delicate fruit. Or if shake harvesting the fruit, the berries will be damaged and will need to be quickly processed. Not only did the breeder and a University panel choose it as having the best flavor, but its top rating for flavor was also verified by a Japanese Company that chose it as the best tasting of 43 samples!” 

The Tundra is by far the hardiest and best growing of the four varieties we have planted at the research station in Erie County (PA).  The Indigo Treat is also doing well. Indigo Gem and Berry Blue have both developed black leaves. We are going to determine this year if the black leaves are from sunburn, mildew, or early dominancy.  Haskap can go dormant as early as mid-August which may be the cause of brown leaves.

Haskapa of Nova Scotia at www.Haskapa.com has a wide variety of products made from Haskaps.  They include syrup, wine, gin, jelly, soap, dried berries, and oils to name a few. This new crop could be grown alongside existing fruit tree orchards, blueberries, raspberries, strawberries, and juice and wine grape vineyards that currently dominate the landscape. If successful, these new crops may serve to supplement the growers’ income, especially in adverse years.

References Cited:

  1. Bors, B., Thomson, J., Sawchuk, E., Reimer, P., Sawatzky, R., and Sander, T. Haskap breeding and production-final report (pp. 1-142). Saskatchewan Agriculture: Regina.
  2. Retamales, J.B., and Hancock, J.F. 2012. Nutrition. In J.B. Retamales and J.F. Hancock (eds.), Blueberries (pp. 103-142). Wallingford: CABI.
  3. Thompson, M.M. 2006. Introducing haskap, Japanese blue honeysuckle. Journal of American Pomological Society 60:4:164-168.
  4. Thompson, M.M. 2008. Caprifoliaceae. In J. Janick and R.E. Pauli (eds.), The Encyclopedia of fruit and nuts (pp. 232-235). Wallingford: CABI.

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.

 

Adding Bubbles to your Hard Cider

By: Denise M. Gardner

At the recent Sparkling Wine Production workshop in PA, our speakers talked a lot about various production methods used to incorporate carbonation into [grape] wine.  But what about for a sparkling hard cider?

For base cider production, the objectives are similar to that of sparkling wine: create a fresh and fruity alcoholic product with high acid, good apple flavor, and a clean nose and palate.  Nutrient strategies during primary fermentation should be considered by the cider maker, as flaws like hydrogen sulfide (H2S) or general reduction (sulfur-containing off-odors) will diminish the enjoyability of the product.  Carbonation has the tendency to enhance the perception of flaws.  Therefore, it goes without saying that sanitation is generally very important during this process in order to obtain a clean product suitable for carbonation.

For producers that struggle with obtaining high-tannin apple varieties, sparkling [hard] cider may offer an alternative to the establishment’s product portfolio.  In sparkling wine production, low tannin concentrations and perceptions are often preferred, as too much tannin may create a harsh mouthfeel with the additional sensory contribution from the carbonation.  This concept may also be applied to sparkling hard ciders.

Malolactic fermentation, MLF, or partial-MLF is determined stylistically by the cider maker.  Stabilization including protein stabilization and clarification should be completed prior to carbonation.  Dependent on the method of carbonation, sulfur dioxide additions may be required at this step, too.

Dependent on the size and capabilities of the cidery, most sparkling wine production techniques can be utilized by hard cider producers to enhance the carbonation of a hard cider product.

  • Bottle conditioning
  • Traditional method (Méthode Traditionelle, previously referred to as Méthode Champenoise)
  • Charmat, or Tank, method
  • Forced carbonation

Bottle conditioning is often used by home brewers as a way to incorporate carbonation in each bottle inexpensively.  The concept is relatively simple: add yeast and some additional sugar to each bottle so that the yeast will ferment the sugar while in the bottle.  Due to the fact the bottle is sealed, the carbon dioxide developed through fermentation will be retained as carbonation in the bottle.  While this is often a preferred method for extremely small operations, the results of this technique are often quite variable, which increases inconsistency amongst the product.  Additionally, the resultant product is not typically clear and residual yeast will settle at the bottom of the bottle.  Sometimes, this noticeable cloudiness and precipitate is not preferred by consumers.  For a good explanation on bottle conditioning, please consider reading this document by Northern Brewer: https://www.northernbrewer.com/documentation/AdvancedBottleConditioning.pdf

The Traditional Method (Méthode Traditionelle) is the common practice that is associated with Champagne production.  In this case, carbonation is produced in the bottle by a second yeast fermentation.  The difference between this method and bottle conditioning is that the residual yeast is removed through disgorgement prior to the addition of a final sugar and stabilization liquid, called the dosage.  This production technique has previously been discussed through the blog post: The Bubbles: Basics about Sparkling Wine Production Techniques, which you can access through the link.

Two ways of riddling sparkling wine at Korbel Wine Cellars, CA. This process is often used during the Traditional Method of sparkling wine (or hard cider) production. Photos by: Denise M. Gardner

Although many wine fermentation suppliers offer various product addition options for hard cider producers, Scott Labs currently offers The Cider Handbook to make addition decisions easier for producers.  Their current product portfolio also features encapsulated yeast products, which some sparkling wine producers have had success in using when utilizing the traditional method of production.

Scott Lab’s 2016-2017 Hard Cider Handbook. Photo by Denise M Gardner.

Additionally, this style of sparkling hard cider can use similar equipment utilized by sparkling wine producers.

The Charmat Method (Tank Method) is becoming more popular amongst local wineries, and can also be utilized by sparkling hard cider producers.  Here, the secondary yeast fermentation occurs inside a sealed tank and then the hard cider is racked off of the lees into a second pressurized tank.  The racked cider maintains the carbon dioxide, carbonation, and the second tank it is racked into can contain the final dosage for the whole volume of hard cider in order to manipulate final sweetness and stabilization.  The advantage to this system is that it retains the fruitiness associated with the product and requires less labor compared to dealing with hundreds of bottles in the Traditional Method.  The downside to this processing option is the initial cost of processing equipment required to retain pressure inside a tank.  As with the Traditional Method, details pertaining to the Charmat Process were previously discussed in the blog post: The Bubbles: Basics about Sparkling Wine Production Techniques.

Finally, one of the easiest methods for obtaining carbonation in your product is through the use of forced carbonation.  Some hard cider producers have found success in carbonating kegs of hard cider or working with local wineries that offer carbonation services.  With this method, the hard cider should be fully produced, stabilized, back sweetened (if applicable) and filtered by the time it is carbonated.