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.
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
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 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.
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.
- Fermenting with Botrytis 101
- Management of Botrytis Infected Fruit
- Managing Botrytis Infected Fruit Fact Sheet
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.
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.
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:
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:
- Fermentation Nutrients
- Malolactic Bacteria
- Yeast Hulls
- Salts for Acid Adjustments
- 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.
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:
- Reviewing YAN and Hydrogen Sulfide Part 1
- Reviewing YAN and Hydrogen Sulfide Part 2
- Yeast Selection and Hydrogen Sulfide
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.
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