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
Based on the number of questions I have received this year about yeast assimilable nitrogen (YAN), it looks like more winemakers are taking it upon themselves to measure YAN on pre-harvested fruit or on incoming juice. This can be a great step in improving wine quality! Measuring YAN offers several benefits to winemakers, including:
- Minimizing the incidence of hydrogen sulfide development in the wine.
- Enhancing varietal character by producing cleaner wines with adequate and specific nitrogen supplementation throughout primary fermentation.
- Minimizing excessive nutrient supplementations, in which left-over nitrogen (after primary fermentation) may act as nutrient sources for spoilage yeast and bacteria.
- Reducing unnecessary work for your employees by minimizing problematic production situations (e., fixing wines with hydrogen sulfide). Such actions could have economic benefit (i.e., reduction in supplies, reduction in time/labor)
Below is a quick refresher for those that may have questions about YAN.
- YAN = Ammonia Concentration + Primary Amino Acid Concentration given in the units: mg N/L (read: milligrams of nitrogen per liter)
- Most suppliers (g., Lallemand, Scott Labs, Enartis, Laffort) will provide recommendations on what to add in low, medium, or high YAN situations. Make sure you consult your handbooks or supplier websites for their product-specific recommendations.
- At the start of fermentation, you want to avoid adding diammonium phosphate (DAP) or complex nutrient additions that contain DAP (g., Fermaid K) when hydrating your yeast. Use hydration-specific products like GoFerm or Nutriferm Energy.
- Most suppliers recommend making 2 additional nitrogen supplementation additions during primary fermentation and after inoculation. If only making 1 nutrient addition after inoculation is practical for you, add your nitrogen supplement at about 1/3 of the way through primary fermentation (e., 1/3 drop in sugar depletion).
A Review: Why to not add DAP at yeast hydration/inoculation
YAN is composed of inorganic (ammonium ion) and organic (primary amino acid) nitrogen components. Amino acids are brought into the yeast cell through transport across the cell membrane. The presence of alcohol and ammonium ions (i.e., DAP) inhibit amino acids from being brought into the cell. This is why winemakers are advised NOT to add DAP at inoculation or at the beginning of fermentation, as yeast can actively absorb organic nitrogen in the juice (aqueous) environment.
Once alcohol concentrations begin to increase, as a result of primary fermentation progression, transport of amino acids from the wine into the yeast cell will be inhibited. Therefore, the primary source of nitrogen will then come from inorganic sources, such as DAP. A more thorough summary of how nitrogen is utilized by yeast can be found at the following pages:
- Wine Made Easy Nutrient Management Fact Sheet
- Cornell University’s FAQs Associated with YAN
- YAN Data Review Over 6 Vintages
- Variations in YAN in the same vineyard sites across multiple vintage years
In general, winemakers can select from three different kinds of nitrogen-based products to add during fermentation:
- Hydration Nutrients (g., GoFerm, Nutriferm Arom, etc.)
- Complex Nutrients (g., Fermaid K, Nutiferm Advance, Superfood, etc.)
- Diammonium Phosphate or DAP
Need more direction on when to add which nutrients? Look no further! We have a practical fact sheet waiting for you at the Penn State Extension website. As a general rule of thumb, remember to make your YAN additions based on the volume of wine that you are treating. For whites, roses, and some reds (e.g., hot pressed Concords), YAN additions will be made based on the juice volume. For most other reds, YAN additions should be based on the must volume.
Dealing with Low YAN Fermentations
Low YAN fermentations are defined as having less than 125 mg N/L in the must/juice at the start of fermentation. In these situations, it’s essential for the winemaker to provide enough “food” for all of the yeast during primary fermentation.
Depending on the reference, most scientific literature will recommend adding up to 200 – 250 mg N/L. This concentration of nitrogen should provide adequate supplementation for the entire biomass throughout the duration of fermentation.
Be aware that if you are using a HIGH NITROGEN DEMANDING YEAST strain (e.g., BM45, ICV-GRE, among others), however, you may be required to add additional supplementation. If you are starting with a low YAN situation and would like to use a high nitrogen requiring yeast strain, we recommend contacting your supplier for specific nutrient addition instructions.
Dealing with High YAN Fermentations
Many suppliers define a high YAN fermentation anywhere above 250 mg N/L. However, some YANs from Pennsylvania grown grapes are at concentrations greater than 400 mg N/L! This YAN concentration can create a challenging fermentation and processing situation for the winemaker.
Due to the excess amount of available nutrients in these situations, yeast can grow and reproduce quickly, which often leads to very rapid and hot fermentations. The speed and temperature of fermentation can affect the aromatics and quality of the wine (i.e., fast fermentations often lead to simpler aroma and flavor profiles). This may not be an issue with some fermentations, but for many white, rosé, or fruit (other than grapes)-based fermentations, aromatic retention should be a priority by the winemaker.
Higher concentrations of the inorganic component of YAN can lead to a high initial biomass of yeast. This is a problem because the rapid increase in yeast populations can lead to starvation by the majority of the yeast by mid- to late-fermentation, especially if there is not enough nutrition to fulfill all of the yeast during fermentation. Yeast starvation leads to yeast stress, and one of the stress responses by yeast is the production and release of hydrogen sulfide. Therefore, having a high YAN at the start of fermentation may cause hydrogen sulfide issues in the wine by the time fermentation is complete.
What should you do if you have a high YAN?
- First, always reference your supplier recommendations. Each year, suppliers publish current guidelines for how and when to add various nutrients during fermentation.
- I’ve found it helpful to document trends in high YAN fermentations. For example, if you notice that a variety with a routine high YAN year-to-year, note the years where hydrogen sulfide becomes an issue. Good record keeping during primary fermentation can remind you what you did during production. You may need to alter these practices for the following vintage year.
- If all else fails, refer to Penn State’s Wine Made Easy Fact Sheet on Nutrient Supplementation during Primary Fermentation
Additionally, high YAN concentrations may leave some nitrogen left over by the end of fermentation and could remain in suspension in the finished wine. This excess “food” could be available for other microorganisms (like acetic acid bacteria or Brettanomyces), which could potentially lead to spoilage problems if the wine is not properly stabilized. In high YAN situations, it is especially important to ensure that the wine is stabilized with adequate sulfur dioxide additions and by minimizing other risk factors (e.g., temperature control of the wine).
It is also be researched that high starting YAN values may led to increased concentrations of ethyl carbamate. Ethyl carbamate is naturally produced by fermentation, but it is a mild carcinogenic compound. For this reason, many countries have legal maximum ethyl carbamate concentrations in wine. For more information on ethyl carbamate, please see this guide published by UC Davis or this Extension report from Virginia Tech’s Enology Grape Chemistry Group.
Our Understanding of YAN is still Developing
Every year, YAN is a big topic of conversation amongst industry suppliers and academics. Current investigations include:
- The impact of primary amino acid uptake as a function of temperature, reported by Cornell University and discussed at the 2016 American Society of Enology and Viticulture (ASEV) – Eastern Section conference (Missouri) in a presentation by Scott Labs.
- YAN recommendations for hybrid varieties produced in the Mid-Atlantic, a topic discussed by Dr. Amanda Stewart from Virginia Tech University during the 2014 PA Wine Marketing & Research Board Symposium. This includes looking at other nutritional factors beyond nitrogen supplementation, which was also discussed at the ASEV-Eastern Conference in 2016 by Scott Labs.
- Optimal nutritional strategies for challenging fermentations, which is often reported in supplier catalogs like the Scott Labs 2016 Handbook
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 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.
“What’s wrong with my wine?” Bringing you ways to improve the quality of your wine by minimizing the effects of wine defects
By: Denise Gardner
Hydrogen sulfide, oxidation, volatile acidity… they happen every year.
But what is a producer to do? How do you even know which wine defect you have going on in the cellar?
Luckily, Penn State Extension offers the Wine Quality Improvement (WQI) short course every January, which was designed specifically for local producers. While Extension currently provides various fact sheets for winemakers in need of addressing various production problems:
- Sulfur-based off-odors, including copper trials for hydrogen sulfide and thiol remediation
- Yeast nutrient management (minimizing the risk of hydrogen sulfide)
- Managing sulfur dioxide
- Volatile acidity
this two-day, sensory-intensive workshop will leave attendees feeling more confident in identifying production problems as they happen in the cellar. We will cover all of those pesky quality defects that occur quite often, even to the best producers:
- Volatile acidity,
- Sulfur-like off-odors (sulfur dioxide, hydrogen sulfide, mercaptans/thiols, and disulfides),
- Unripe, green flavors (methoxypyrazines),
- Cork taint (TCA), and
- Brettanomyces (Brett) associated flavors
Not only will you be exposed to individual standards of each one of these defects, a series of lectures will review ways to prevent the defects during production and how to treat them if they occur in your wine.
Additionally, the WQI will host a series of hands-on rotations to expose attendees to wine sensory evaluations and improve each individual’s tasting ability:
- Using wine defect kits to train yourself, cellar personnel, and tasting room staff in identifying problematic wines. It’s a good idea to train as many employees in sensory-related wine defects because everyone’s sensory abilities differ. For example, your winemaker may not be able to smell or taste hydrogen sulfide! If that is the case, it’s essential to find another employee that can screen wines before they are bottled for this common defect. Otherwise, a winery may send faulty wine straight out of the tasting room! BONUS: All attendees will walk away with their very own defects aroma kit to take back with them and use for in-house training sessions.
- Learn how to make sensory standards to train cellar personnel and improve their tasting skills. Have you ever wondered how “experts” pick up the smell of fresh currants in wine? Or what makes a wine “jammy” instead of “fresh fruit?” We’ll teach you how to make standards using materials that can be found in the average household and show you how to utilize the standards for sensory training at the winery or tasting room.
- Discover your threshold for these wine defects. Using the Department of Food Science’s state of the art Sensory Evaluation Center, all attendees will have the opportunity to figure out how easily they can smell several technical wine defects. Who knows? You may find out you can smell one – or more – of these defects!
- Evaluate commercial wines. Each attendee has the opportunity to bring a bottle of wine with them that they would like evaluated. We’ll code each wine so that all attendees don’t know what they are tasting, and taste them as a group to provide feedback to each individual that submits a wine.
- Practice tasting benchmark wines. I am often asked how I know what makes a good Cabernet or Chardonnay. The answer: I’ve done A LOT of sensory training… but so can you! Half of understanding wine quality is learning to identify faults and the other half is learning subjective quality parameters, which may be variety, style, or regionally specific. While the focus of the WQI is to teach attendees how to identify faults or defects, we’ll take some time to run a benchmark wine tasting session using well-known commercial wines to emphasize other quality parameters. Learning wine styles and common wine descriptors helps you get in tune with sommeliers and consumers. Plus, it helps create goals in the winery for the style of wine you are producing.
This workshop has always been rated highly amongst industry producers. Many have complemented our ability to make producers aware of problem-points in the winery, and change those places in production to avoid future mistakes.
Another great part of this program is learning how to fix these problematic wines when issues occur. As we all know, there is often not one way to fix a wine when something goes wrong, and more often than not, problem wines usually have more than one problem! What’s a winemaker to do?
Interested in this program? Hopefully you can join us! More information on the full agenda, cost, and registration for the WQI can be found on our Penn State Extension registration website. Have more questions on this workshop? Feel free to email Denise Gardner, Extension Enologist, at firstname.lastname@example.org.
By: Denise M. Gardner
By definition, wine defects are typically undesirable and unpleasant characteristics that occur in wine as a function of poor viticulture, winemaking, or storage techniques. The words “fault” and “defect” can be used interchangeably.
Perception of wine defects varies from individual to individual, which emphasizes the importance of sensory evaluation training amongst winemakers. If a winemaker is genetically blind to sensing a specific defect, and there is no secondary personnel available to “double check” the wine, wines may be bottled and sold to consumers faulted.
However, several wine defects can also be evaluated analytically throughout various stages of wine production. This emphasizes an importance of understanding analytical evaluation of wine and how it relates to wine quality.
While there is a lot of pride that goes into being a winemaker, wine defects happen. To everyone.
Sometimes these defects may reach concentrations that throw the wine out of balance or are beyond traditional remediation techniques. In these instances, a winemaker may turn to the use of distillation to treat wine defects with the hope of producing a distilled spirit that does not retain the perceived defect.
Distillation is used as a technique to concentrate ethanol from a fermented beverage. Typical spirits are produced from low-alcohol grain- or fruit-based fermented beverages. Pure ethanol, which has a lower boiling point (78.5°C) than water (100°C), vaporizes prior to water when heated. This physical property allows the separation of ethanol from water when it is properly heated. However, fruit-based fermented beverages are complex mixtures, and separation of other components, like odorous aroma compounds, may also be separated from the initial beverage.
The table below outlines the boiling points of common wine defects.
Based on this table, one may assume that many of these components can be easily separated from ethanol and water in the base product. In fact, older research literature has shown the reduction of many aldehyde-based compounds, some associated with wine oxidation, in commercial brandies produced in California (Guymon 1970). However, several compounds including hydrogen sulfide, “reduced” sulfur-containing compounds, sulfur dioxide, 2,4,6-trichloranisole (TCA, cork taint), methoxypyrazines, and some Brettanomyces-related aromas may be concentrated and retained in the final distillate.
Separation of aromatic compounds (volatiles) is not based on boiling point alone due to the fact that the base material, wine, is a complex mixture. Separation of volatile components will also be based on the relationship that compound has with ethanol or water (Léauté 1990). Many of these compounds like TCA, methoxypyrazines, or sulfur-containing compounds may be present in the base wine in such low concentrations that it may be challenging to effectively separate from the ethanol. However, some distillers point to the use of a copper still to help interact with sulfur containing compounds (such as hydrogen sulfide or thiols/mercaptans) to reduce these aromas in the distillate. One study found that dimethyl sulfide (DMS) was reduced when a copper still was used for distillation as opposed to a non-copper still (Fairia et al. 2003).
Concentration is also a factor for things like TCA or many methoxypyrazines, which are commonly present in wine in part per trillion (PPT) concentrations. In a study that evaluated distilled hard apple cider, the researchers identified several descriptors by use of olfactometry associated with making the distillate “defective:” sweat, vegetal, phenolic, old sponge, pyrazin, solvent, rot, mold, and herbaceous (Guichard et al. 2003). While the source of these sensory descriptors was not linked to any one aroma compound, some of these terms, like herbaceous and vegetal may be associated with methoxypyrazines or other aldehydic aroma compounds. Old sponge, rot, or mold may be associated with TCA and other spoilage volatiles. The study by Guichard et al., however, exemplifies how human perception of distillate dictates perceived quality.
Previous research associated with 4-ethyl guiacol (4EG) has shown retention of this aromatic compound in the distilled component called “the hearts.” Volatile components retained in the hearts have low boiling points and are typically soluble in alcohol (Léauté 1990). Therefore, retention of this odor compound may be altered based on where a distiller makes his or her cuts for distillate retention. In the case of batch distilling, it may be possible to further reduce these compounds by re-distilling a batch several times.
Solutions for Winemakers
The overarching message pertaining to distillation to remediate wine faults is that is not a fix-all solution to “cure” wine defects. In some cases, the winemaker may go from dealing with a faulted wine to receiving a faulted distilled spirit.
Many base wines used for distilled spirits are selected for flavor neutrality and nuance. Wines that contain faults are likely to contribute some additional nuance flavors that may not be expected in the final distilled spirit. Winemakers need to make sensory decisions to determine if a potential unexpected nuance flavor in the distilled spirit would be considered detrimental to the quality of their final product. If so, remediating the wine defect through alternative means may be necessary.
As with many issues pertaining to wine defects, the best way to ensure quality is to try to avoid the defect before it occurs in the wine. Receiving high quality raw material (i.e. grapes), using proper sanitation techniques, and managing oxygen exposure during wine processing can help winemakers avoid many wine defects.
More Information on Distilling Wine Defects
Previous Penn State Food Science undergraduate student, Erin Donnelly, published her review pertaining to the use of distillation to “cure” wine defects. This paper was later refined and published in the March-April 2015 Vineyard & Winery Management trade magazine, titled “Distillation of Faulted Wines.” Both articles are great references for further information on this topic.
Guichard, H., S. Lemesle, J. Ledauphin, D. Barillier, and B. Picoche. 2003. Chemical and sensorial aroma characterization of freshly distilled calvados. 1. Evaluation of quality and defects on the basis of key odorants by olfactometry and sensory analysis. J. Agric. Food Chem. 51: 424-432.
Guymon, J.F. 1970. Composition of California commercial brandy distillates. Am. J. Enol. Vitic. 21(2): 61-69.
Faria, J.B., V. Ferreira, R. Lopez, and J. Cacho. 2003. The sensory characteristic defect of “cachaҫa” distilled in absence of copper. Alim. Nutr. 14(1): 1-7.
Léauté, R. 1990. Distillation in Alambic. Am. J. Enol. Vitic. 41(1): 90-103.
By: Denise M. Gardner
In 1857, Louis Pasteur was asked to investigate why some fermented beers would sour while others would ferment into good, quality products. Pasteur discovered that beers, wines and many other fermented products were fermented by microorganisms called yeast. However, when a spoiling effect would take place, he found that the microorganisms present in the beverage were much smaller than the yeast cells. Pasteur concluded that it was these bacteria that caused wine to spoil into a vinegar-like product. Fast-forward over 150 years later, and winemakers still deal with these spoilage microorganisms in wine today.
Volatile acidity (VA), specifically the measurement of the wine’s volatile acids, can be a challenging issue in many young and old wines. In wine, the primary acid that contributes to volatile acidity is acetic acid, which is also the primary acid associated with the smell and taste of vinegar. In my experiences traveling throughout the Mid-Atlantic, I have found many winemakers assume that they will be able to taste acetic acid before it becomes a problem in the wine. However, I would like to make the argument that by the time a winemaker tastes acetic acid (or vinegar) the problem has already gone too far. This blog post explains that perspective.
The sensory threshold for acetic acid is between 0.7 – 1.2 g/L for most individuals, and many are surprised at how challenging it can be to smell acetic acid before the levels rise near legal limits. As defined by the Standards of Identity in the Code of Federal Regulations (27 CFR), “the maximum volatile acidity, calculated as acetic acid and exclusive of sulfur dioxide is 0.14 g/100 mL for red wine (1.4 g/L) and 0.12 g/100 mL (1.2 g/L) for white wines.” There are some allowances for higher maximum VA concentrations for wines produced from unameliorated juice up to 28°Brix.
The assumption many winemakers make is that they will be able to smell or taste acetic acid (vinegar) before it reaches the legal limit, as vinegar is easily recognized by most people. However, commercial vinegars generally contain 3 – 9% (30 g/L) acetic acid concentrations, which is much higher than 1) the associated threshold and 2) the legal concentration allowed in wines.
Additionally, the smell and taste of VA is also composed of acetic acid’s oxidative breakdown product, ethyl acetate. Ethyl acetate has an aroma that is similar to nail polish or nail polish remover. Its threshold is much lower than acetic acid at 100-120 mg/L (0.10-0.12 g/L). While it is not necessary for high VA wines to contain the ethyl acetate aroma in addition to a high acetic acid concentration, both usually go hand-in-hand. In some instances, the detected concentration of acetic acid can be under the 0.7 g/L threshold with a high (>100 mg/L) concentration of ethyl acetate, contributing to the “high VA” nature of the wine in question.
Enologists measure acetic acid concentration simply because it is easier and more affordable than measuring the ethyl acetate content in the winery. Additionally, legal limits for volatile acidity are defined by the acetic acid concentration.
Where does VA come from?
The primary sources of acetic acid in wine are from several spoilage yeasts and bacteria. While some strains of yeasts (Kloeckera, Brettanomyces, Candida) and lactic acid bacteria can contribute to the acetic acid concentration, many wines suffering from VA spoilage is due to the presence of acetic acid bacteria. To a winemaker’s dismay, acetic acid bacteria are relatively ubiquitous in the vineyard and winery.
In the vineyard, higher concentrations of acetic acid bacteria have been affiliated with poor quality fruit and wetter growing seasons. Sour rot, which typically makes grapes smell like vinegar while hanging on the vine, is of particular interest. Zygosaccharomyces and Hanseniaspora are two additional spoilage yeast genera that may also contribute to the volatile acidity of wine produced from sour rotted grapes.
Biofilms of acetic acid bacteria are also common in the cellar. Drains, exterior surfaces of tanks (especially those that have dripping juice or wine on them), barrels, vents, and floor surface crevices have all been isolated as harboring sites for acetic acid bacteria growth. The lack of adequate equipment/cellar repairs, cleaning, and sanitation can increase the risk for acetic acid bacteria contamination in the cellar.
Volatile Acidity during Winemaking
Acetic acid bacteria are obligate aerobes, indicating that they need oxygen to grow and proliferate. Many considerations can be taken during wine processing to control oxygen exposure.
Like many other microorganisms affiliated with wine production, acetic acid bacteria can be managed with proper sulfur dioxide treatments, adequate temperature control, thorough sanitation practices, and appropriate oxygen management strategies. As acetic acid bacteria need oxygen to grow, reducing oxygen in the wine is a good way to minimize potential growth.
Many winemakers experience acetic acid bacteria growth during barrel aging. However, if barrels are properly topped off every 1-2 months to minimize oxygen in the headspace, and wines are treated with sulfur dioxide (according to the wine’s pH), acetic acid bacteria growth can be managed through this oxidative processing step. It is important to note that winemakers should avoid topping barrels too frequently, as this practice breaks the natural vacuum created by evaporative loss in the barrel. The vacuum minimizes oxygen availability for microorganisms that may be present in the wine.
Other winemaking practices have been affiliated with enhancing acetic acid bacteria growth or increased levels of VA in the finished wine. These include:
- Cold Soaking
- Natural or Native Fermentations
- Sluggish or Stuck Fermentations
- Prolonged Headspace (Oxygen) or Ullage in Tanks and Barrels
These processes are affiliated with higher incidences of high VA wines because they open opportunities for acetic acid bacteria or spoilage yeast growth. This may contribute to increased acetic acid or ethyl acetate concentrations due to prolonged exposure to oxygen. Yeast selection can also play a role in this. It is well documented that Saccharomyces cerevisiae contributes minimal quantities of acetic acid (<0.5 g/L) to a wine by the end of primary fermentation. This concentration is less than threshold, and often provides “lift” or “enhancement” of the fruity aromas and flavors in the wine.
Research pertaining to cold soaking has shown no impact and increased concentrations of volatile acidity. Some of these conflicting results may pertain to the way cold soak is executed. Those using refrigerated environments may find spots throughout the tank or bin that are warmer than the surrounding fruit. These hot spots can encourage acetic acid bacteria or spoilage yeast growth at a time when the wine is generally unprotected by sulfur dioxide and exposed to oxygen. Even if winemakers treat crushed fruit or must with sulfur dioxide, it is often less effective due to the increased amount of surface area affiliated with all of the unfermented berries.
Cold soaking that includes adequate mixing in temperature controlled tanks to drop the temperature quicker appears to have a more positive effect on the volatile acidity of the finished wine. The use of dry ice into the center of a fermentation bin has more frequent positive outcomes as well. Not only does dry ice adequately cool the grapes/must, but it also displaces some of the oxygen available for acetic acid bacteria growth.
Natural or native fermentations can encourage acetic acid bacteria or spoilage yeast growth before primary fermentation takes off, but this practice is unpredictable and inconsistent. Stuck or sluggish fermentations run the risk of acetic acid spoilage due to the fact that little carbon dioxide is given off during the later stages in fermentations. Without adequate gas displacement, the surface of the wine is exposed to oxygen, which can support spoilage yeast and bacteria growth. Additionally, spoilage microorganisms will compete for nutrients with the struggling yeast populations trying to finish the fermentation.
Contamination in the Winery
The other issue wineries should be aware of is sustaining biofilms throughout the winery and cross contamination. While contaminating a wine with spoilage yeast or bacteria may not result in a spoiled wine (through proper fermentation management), it increases the risk for potential spoilage.
Winemakers should watch for biofilm sites that can harbor spoilage microorganisms:
- Exterior surfaces of tanks, valves, barrels, etc.
- Drains, especially drains that are not regularly cleaned
- Crevices or cracks in floors
- Wooden equipment, including barrels
- Hose lines or connecting points
- Use of unsanitized wine thieves
When taking barrel samples, winemakers should carry a bucket of no-rinse sanitizer (e.g. citric-sulfur dioxide solution, 70% ethanol) to soak the wine thief in before it enters a barrel. The thief should be sanitized before and after each sample is taken from a barrel. In fact, any vessel that will hold a solution or addition to be added to the wine should be pre-cleaned and pre-sanitized before it touches the material that will go into the wine. This is a common food sanitation practice that is carried out by commercial food productions, and wine is no exception to this rule.
Cleaning and sanitizing the wine thief is one of the easiest ways to avoid cross contamination of spoiled wine into clean wine. Additionally, minimizing bacterial growth in a barrel ensures better cleanliness of the barrel. Barrels that contain higher populations of bacteria in a wine are more difficult to clean and rid of bacteria once the barrel is emptied. Given the investment associated with barrel purchases, it is within the winemaker’s financial interest to ensure proper sanitation techniques are utilized by all cellar personnel.
Measuring Volatile Acidity
Luckily, most small commercial wineries can invest in a cash still to monitor the volatile acidity concentration from post-primary fermentation through bottling. In fact, monitoring VA is a good and easy way for winemakers or enologists to monitor spoilage through the life of the wine during its stay in the winery.
I have found that many people are initially intimidated by the cash still, but it is a rather simplistic piece of equipment to use once properly trained.
The cash still is used to carry out a steam distillation process, which separates the acetic acid from the wine. Wine and an anti-foam agent are poured into the interior bulb of the cash still. Distilled water is boiled in the exterior bulb, which surrounds the interior bulb. The boiling water slowly heats the wine in the interior bulb, and as the wine heats up, various volatile components (i.e., water, aroma compounds, acetic acid, etc.) are released into the headspace of the interior bulb. These gases, some of which include the volatile acid, acetic acid, are condensed into a liquid as it cools while traveling up the interior bulb and into the condenser. This condensed liquid is collected from the condenser tube, and a titration is used to determine the concentration of acetic acid in the liquid.
A good cash still will cost the winery ~$900. For an adequate protocol, please click here.
During the winemaking process, volatile acidity should be evaluated, at minimum:
- After primary fermentation
- After malolactic fermentation
- Periodically through storage
- When a film is found on a given wine
Fixing High VA Wines
Why all of this information about volatile acidity?
This is one wine defect that is much easier to prevent than to remediate. In lower VA-issue wines, blending with a non-contaminated and lower VA wine is often selected. It is important for winemakers to ensure that the high-VA wine is sterile filtered (confirmed by analysis) and moved into a properly sanitized storage vessel until it can be blended.
Higher VA wines (>0.7 g/L) are a greater issue, and it may be challenging to blend them away or they may have to be blended away in small quantities over time. The only practical option for wines with a very high VA is the use of reverse osmosis (RO), which can often be contracted out to various wine technology companies. RO can be costly and depending on the company, it may not be a practical solution to minimize ethyl acetate concentrations.
Ignoring the flaw is not recommended, as VA is regulated by the TTB and limits are set for various wine styles. Please visit the TTB website here for more information on volatile acidity regulations [27 CFR 4.21(a.iv.)].