Tag Archive | sulfur dioxide

The Cellar after Harvest’s Dust Settles

By: Denise M. Gardner, Enology Extension Associate

Most likely, all of the wines from the 2016 vintage are happily settling away in tank or barrel at this point.  After such a busy time, his leaves winemakers with that tricky question, “What do I do now?”

Monitoring Malolactic Fermentation (MLF)

Now is a good time to make sure you are monitoring your malolactic fermentations.  Ensure all of your barrels or tanks have been appropriately inoculated, or have started naturally, and get some initial readings on the malic acid concentration.

If you have a spectrophotometer, you can purchase enzymatic kits to measure the concentration of malic acid in your wine over time.  Wines with less than 30 mg/100 mL of malic acid are considered “dry” for MLF or MLF-stable for bottling.

However, winemakers can also monitor malic acid degradation through the use of paper chromatography kits.  These kits are easy enough for home winemakers to use and can also be applied at the commercial level.

MLF paper chromatogram. This image shows the paper after it has dried, where the spots are pertaining to the acid standards and the acid separation for a wine sample. Wine samples above have not completed MLF due to the fact there is a noticeable dot of malic acid in each sample.  Photo by: Denise M. Gardner

MLF paper chromatogram. This image shows the paper after it has dried, where the spots are pertaining to the acid standards and the acid separation for a wine sample. Wine samples above have not completed MLF due to the fact there is a noticeable dot of malic acid in each sample. Photo by: Denise M. Gardner

Paper chromatography works by separating tartaric, malic, and lactic acids from a wine sample (Figure 1).  In addition to blotting small drops of your various wine samples, each paper must also contain 3 standards to show the spots documented by the three acids (tartaric, malic, and lactic).  While paper chromatography is not the best at concentrating how much of each acid remains in the wine, you can get an idea when the bulk of malic acid is converted to lactic acid (i.e., MLF is completed) when the malic acid spot associated with the wine samples disappears.

For a complete protocol on paper chromatography, please see this page: https://www.midwestsupplies.com/media/downloads/421/malolactic_chromatography_kit.pdf

Checking Wines for Off-Flavor Development

It’s also a good time to check wines for hydrogen sulfide (H2S) or sulfur-base off-odor aromas, and volatile acidity (VA), especially for wines that you will want to bottle early in the new year.

Hydrogen sulfide can be treated with copper sulfate.  Penn State Extension offers a great 2-page fact sheet on how to run a copper screen to determine if the wine requires copper sulfate, and a copper bench trial in order for you to assess how much copper is needed to treat the hydrogen sulfide: http://extension.psu.edu/food/enology/wine-production/wine-made-easy-fact-sheets/sulfur-based-off-flavors-in-wine

Now is also a good time to know what the VA is in your wines, especially those that will be seeing some aging.  This is incredibly important to get a baseline value of the VA.  That way, if a problem emerges in the future, you will have an indication how much the volatile acidity has increased.   Penn State Extension also offers a 2-page fact sheet explaining why knowing volatile acidity is important, provides protocols for its analysis, and how to mediate high VA situations: http://extension.psu.edu/food/enology/wine-production/wine-made-easy-fact-sheets/volatile-acidity-in-wine

If you are having problems identifying these key defects in your wine, don’t forget that the annual “Wine Quality Improvement” Short Course is just around the corner in January.  For more information on this workshop and its registration, please go here: 2017 Wine Quality Improvement (WQI) Short Course

Cellar Maintenance

Now is also a good time to clean up any leftover sore spots from the chaotic harvest season:

  • Clean up places in the cellar that have gotten dirty or have become areas that are accumulating materials that should otherwise be put away.
  • Manage all of your harvest records.  Make sure all of the wines have the basic wine chemistries (e.g., pH, TA, residual sugar, alcohol, free and total SO2, malic acid, and volatile acidity) in the record book.  It is easy to forget all of these details as time progresses.
Running basic chemical analysis on your wines and updating records is an essential component of making quality wine. Photo by: Denise M. Gardner

Running basic chemical analysis on your wines and updating records is an essential component of making quality wine. Photo by: Denise M. Gardner

Summer in the Cellar

By: Denise M. Gardner

As the growing season turns into full swing, now is the time to get things tidied up in the winery and prepare for this vintage’s harvest season.  The cellar offers the advantage of being relatively cool in the summer months, so it offers an oasis away from the beating sun or those rainy, humid days.  Managing some time for the up-and-coming harvest is a good way to keep cellar work current.  Otherwise, the summer months can appear rather dull in the cellar.  Here’s a list of considerations for the cellar crew:

Give your wines a regular analytical check

For anything that is sitting or aging in the cellar, now is a good time to schedule quality control monitoring.  Wines in barrel need regularly topped off (every other month or every other 2 months) and checked for free sulfur dioxide concentrations if they have completed malolactic fermentation (MLF).

There’s a lot of good information out there on sulfur dioxide.  If you feel slightly uncomfortable with sulfur dioxide additions or analysis, please refer to these current informational pieces that can be a valuable resource to any winemaker:

Wines that are getting ready to be bottled should go through a full analytical screen and recorded into the lab record books.  This will provide insight for the winemaker in terms of how the wine should progress or need altered prior to bottling:

  • pH
  • titratrable acidity (TA)
  • residual sugar
  • residual malic acid concentration and malolactic fermentation completion
  • free and total sulfur dioxide
  • cold stability
  • protein (heat) stability
  • volatile acidity (VA)
AO apparatus set up to measure free sulfur dioxide. Photo by: Denise M. Gardner, Penn State Extension Enologist

AO apparatus set up to measure free sulfur dioxide. Photo by: Denise M. Gardner, Penn State Extension Enologist

For more information pertaining to how to set up wine analysis in your winery, please refer to Penn State Extension’s website on “Starting a Lab in a Small Commercial Winery.”  Information on how to utilize analytical testing labs to the advantage of the winery can be found on the Penn State Extension website, “Wine Analytical Labs.”

For those wineries that have not previously measured cold stability, read Virginia Mitchell’s report on “Cold Stability Options for Wineries,” which explains the importance of testing and how to best treat your wines.

For more information on wine stabilization (sulfur dioxide additions, cold and heat stabilization), please refer to our previous blog post on “Stabilizing Wines in the Cellar.”

Get wines ready for blending or finishing

Now is a good time to pull samples of those wines that you are planning on bottling prior to harvest.  After getting a good analytical evaluation, make sure you check the wines for their sensory perception.  Is the wine at the caliber of quality that you were expecting?  If no, what can you do to fix the wine and get it ready for bottling?  Utilize fining agents or product additions to tweak the wines and enhance the quality.

Also consider blending.  Blending can be a tool to help mitigate problem wines.  But blending can also help you create a spectacular wine out of several great varietals.

Always remember to prepare bench trials before making changes to the entire tank or barrel of wine.  Make sure that several people evaluate the wine and give you their individual evaluation.  Have people write down their perceptions, as opposed to talking in a group, to avoid the power of persuasion and to minimize tasting insecurities.  This practice will give you a more honest, objective evaluation of the wine.

Prepare for Bottling

The summer months are the ideal time to get your wines bottled and ready for release.  Most wines need at least 2 to 6 months of bottle conditioning (i.e., time in the bottle before sale) to stabilize and minimize the effects of bottle shock.

Bottling is a time intensive process and requires a bit of planning by the cellar crew.  Prepare a calendar for bottling days to ensure that all supplies are received for bottling, that wines are fully ready to be bottled, and that there is adequate time to get everything bottled prior to the estimated start date of harvest.  For information pertaining to bottling considerations – how best to sanitize and monitor sterile filtration integrity – please refer to our previous blog post titled, “Bottling Tips and Considerations.”

Take Inventory

Now is a good time to go through all of the supplies that are currently available in the winery and record how much you have of each.  Recording inventory each year is a good way to evaluate what supplies are being purchased, what is being used, and what supplies are typically left over.  It is possible for wineries to find some redundancies through this exercise and identify places to save money.

Suppliers’ “Free Shipping in July” promotions are just a month away!  So being prepared with an accurate inventory can release some stress from the winemaker when it comes to ordering this season’s harvest supplies.  Things to consider include:

  • Yeast and Malolactic Bacteria
  • Yeast Nutrients
  • Any Enological Agents (e.g., Enzymes, Tannins, Polysaccharides/Inactivated Yeasts)
  • Fining Agents
  • Sugar and Acid
  • Potassium Metabisulfite
  • Cleaning and Sanitizing Agents

Make sure that all of the materials currently stored in the winery are being stored properly (i.e., dry chemicals away from wet chemical storage, food grade away from non-food grade, and the requirement that some may need stored frozen), according to the supplier’s recommendations, and that their expiration date has not expired.  For some expired products, some suppliers may be evaluating their efficacy of the product past the expiration date.  If you contact the supplier, you may be able to find an extended expiration date so that the product can be retained.  Otherwise, expired products should be thrown out and re-ordered.

Additionally, going through an equipment inventory can be advantageous.  Make sure all processing equipment is getting prepared to get a good cleaning and sanitizing regimen prior to the start of harvest.  Unused equipment should not be a storage vessel for left-over, dirty rice hulls or mouse droppings.  Use the summer months to check all of the equipment and make sure it is functioning properly.  If there are problems with equipment, it is best to identify it over the summer and, hopefully, get serviced before the start of harvest.  Don’t forget to check tank valves, pumps, inspect hoses for cleanliness, and all of the processing equipment.  Using an inventory, or check sheet, is a good way to ensure equipment is up to par is a good way to keep track of everything’s condition.  Also, evaluating barrel needs and tank space available for harvest can be added to the inventory sheet.

If you have a wine lab, now is also a good time to check the chemical and supply inventory in the lab.  Remember – free shipping in July is just around the corner!  Document expiration dates of chemicals and make a list of new chemicals, analytical standards, or equipment (e.g., hydrometers, pipettes, pipette bulbs, sampling bottles, etc.) that should be purchased prior to harvest.

Inventory all of your supplies to get prepared and organized for the upcoming harvest. Photo by: Denise M. Gardner, PSU Extension Enologist

Inventory all of your supplies to get prepared and organized for the upcoming harvest. Photo by: Denise M. Gardner, PSU Extension Enologist

Take time to evaluate and write SOP’s

Standard Operating Procedures, SOP’s, can help minimize the chaos during harvest.  Having up-to-date SOP’s in the cellar and lab will help minimize the number of times people will always have to ask “the boss” for help.

If you don’t have SOP’s, consider starting small and documenting protocols for things like lab analysis.  Plenty of resources (e.g., websites, text books) are available and can be used to create a standard protocol that works for your winery.

After tackling lab analysis, consider writing an SOP for harvest operations.  Think about writing an SOP for each piece of equipment that your harvest team will need trained on.  Take the crusher/destemmer for example:

  • How is the crusher/destemmer hooked up?
  • How to prepare the crusher/destemmer for fruit arrival (include cleaning and sanitizing procedures).
  • Do you have validation measures to ensure that the equipment is properly cleaned (a visual evaluation? Some sort of analytical testing?)?
  • Do you have a record system that documents the equipment has been properly prepared, cleaned, and sanitized?  If so, where is that documentation and how does your staff document this step?
  • What is the protocol for running the crusher/destemmer?  What safety features should all employees be trained on?  Document all safety procedures.
  • How is the crusher/destemmer cleaned and sanitized after each lot (varietal) of fruit that is run through the equipment?
  • How is the crusher/destemmer cleaned and sanitized after each processing day?  Where is the equipment stored and how is stored?

Winemakers can also document processing decisions.  For example, if you know that you are going to process Vidal Blanc every year, consider writing an SOP specific for how the Vidal Blanc is processed.  Write out each step, the quality control checks (i.e., checking fruit chemistry or monitoring fermentation) and what processing aids are typically added to the Vidal (e.g., yeast, enzymes, etc.).

Winemakers should also have an SOP ready for when fruit arrives to the winery in less than ideal conditions.  For information on what winemakers should consider, please read the two articles on Penn State Extension’s website titled “Producing Wine with Suboptimal Fruit.”

Botrytis disease pressure on Pinot Grigio grapes. Photo by: Denise M. Gardner

Botrytis disease pressure on Pinot Grigio grapes. Photo by: Denise M. Gardner

Having a fully functional and trained cellar crew is a good foot forward as the harvest months approach.  While preparation is tedious, it can save some time and resources during the busy harvest season… and hopefully, minimize the chaos!

Production Tips for the Home Winemaker

By: Denise M. Gardner

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

Concentrate – Grapes – or Juice

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

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

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

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

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

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


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

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

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

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

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

bottles cleaned and sanitized

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

Use Nutrients during Fermentation

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

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

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

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

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

Manage Oxygen Exposure

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

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

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

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

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

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

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

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

Fully bottled wine. Photo by: Denise Gardner

Fully bottled wine. Photo by: Denise Gardner

Avoid Making Wines in Aromatic Environments

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

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

More Resources

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

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

Stabilizing Wines in the Cellar

By: Denise M. Gardner

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

Monitor Sulfur Dioxide Concentrations

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

Proper sanitation and sampling is required for best analytical results:

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

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

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

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

Cold (Tartrate) Stabilization

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

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

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

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

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

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

Protein (Heat) Stabilization

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

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

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

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

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

Bench Trials

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

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


References Cited

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

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

Additional Resources

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

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

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

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

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

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


Considerations and Tips for Wine Bottling

By: Denise M. Gardner

It’s bottling season!  Wineries are gearing up for the current growing season and another harvest.  Now is the crunch time to get everything from last year’s vintage out of tank and barrel, and into bottle.  Bottling is time intensive and tedious for a winery of any size, and it’s easy to leave the bottling line with contaminated wine bottles.

Bottling day in the Food Science Building, 2015

Bottling day in the Food Science Building, 2015

In fact, previous research has shown that even when sterile filtration steps are properly performed, over between 39-58% of the bottles leaving the bottling line end up with yeast in the bottle (Neradt 1982).  Renouf et al. (2007) found that using sterile filtration (0.45 micron absolute filter or lower) was the only way to eliminate most microorganisms from the wine during bottling.  However, in bottles that contained microbial populations upon bottling, Brettanomyces was able to bloom in the bottle after 6 months of storage, and increase 4-EP and 4-EG volatile phenol concentrations within 10 months post-bottling (Renouf et al. 2007).  In fact, long term storage of red wines infected with Brettanomyces found this spoilage yeast became the dominate microbial population in the bottle, outcompeting most other microorganisms (Renouf et al. 2007).  Yikes!

Bottling is one of the most important steps to retain wine quality at the winery.  Therefore, this blog post will focus on a number of bottling considerations for wineries:

  • Make pre-bottling additions before bottling day

Most product additions, including sulfur dioxide, potassium sorbate, gums, sugar, etc. require at least 24 hours of stabilization in wine before it can be sterile filtered and bottled.  There are some exceptions, and some products may require longer stabilization time or need to be added during bottling, after filtration.  You should rely on the advice of your product supplier when working with new additives.  Additionally, some filter suppliers recommend making large sugar additions to wine at least a week before filtration.

If you are making the final sulfur dioxide addition the day before bottling, make sure you measure the concentration of free sulfur dioxide in the tank prior to bottling.  Take multiple samples throughout the tank to ensure that the sulfur dioxide has penetrated all sections of the wine.  If the sulfur dioxide is not high enough to reach the 0.85 ppm molecular level, it is best to alter additions and wait to bottle another day.  For more information on sulfur dioxide additions at various wine pH’s, please click here.

  • Cleaning…

Whether you have a manual bottling and capping system, or a high-tech bottling line, physically cleaning the bottling line is essential to maintaining proper hygiene in the winery.  Bottling is one of the key areas where the quality of the product can greatly be degraded.  Have brushes specific for the bottling line, and utilize detergents that break down wine debris or environmental dust.

Some bottling lines will require personnel to remove valves, hose lines, etc. to physically clean off debris or biofilms.  Following cleaning operations, proper sanitation is essential to reduce microbial contamination through the bottling process.

*Note: The use of potassium sorbate will not inhibit contamination of your wine through bottling.  Only proper sanitation techniques can reduce microbial populations and minimize risk of microbial spoilage in the bottle.

  • …and Sanitation of the Bottling Line

As mentioned above, proper sanitation reduces microbial populations within food equipment and the surrounding environment, in order to reduce the risk of potential contamination within the packaged product – in this case, wine.  While greatly underestimated, the surrounding environment is a potential contamination point in wineries, especially during bottling.  Aseptic bottling operations are not necessary to maintain good hygiene, but it is often recommended that the bottling line be isolated within the winery to avoid large air movements while wine is packaged.  This helps to avoid yeast, which are ubiquitous, contamination during the bottling process.

Floors, walls, and drains should be easily accessible and cleaned in the bottling area to help reduce environmental contamination.  Routine environmental sanitation will also help reduce the risk of contamination.

Additional primary sources of contamination on the bottling line have previously been identified by Neradt (1982):

  1. Filler/Fill spouts
  2. Corker
  3. Bottle sanitizer
  4. Bottle mouth
  5. Filter
Capping a bottle of wine during bottling.

Capping a bottle of wine during bottling.

Proper sanitation of the bottling line first requires proper cleaning to remove all physical dirt and debris.  Otherwise, the sanitation step is literally “cleaning dirt.”

Water chemistry, temperature, and contact time all affect the efficacy of sanitation.  The use of soft water is often recommended for sanitation to avoid hard water residues that can harbor microbial populations.

The minimal temperature-time combination to sanitize equipment using hot water is 180°F (82°C) for at least 20 minutes.  This temperature must be obtained at the coldest point in the bottling line.  For bottling operations, this will be where water leaves the system.  Butzke (2010) notes: “…that humans perceive water as painfully hot at temperatures just above 42°C (108°F).”  Therefore, temperature readings should be taken with a calibrated, food-grade thermometer.

Individuals should take caution when working with scalding material or any chemical agent during the sanitation step.  Always remember to ensure that employees have proper safety equipment and adequate ventilation.

Note that if you are using hot water, heat, or steam to sanitize the bottling line, you will need to bring the equipment back to the temperature of the wine to avoid cooking the first few gallons of wine that flow through the bottling line.  Do not use tap water to change the temperature, as this will ruin the purpose of the sanitation step.  Some wineries prefer to lose the first few gallons of wine, while others will follow a heat step with cold acidulated-sulfur dioxide mix.

Fill heads are an easy source of potential contamination.  Periodically throughout bottling (i.e., every hour, or every time that breaks are taken), these can be sprayed or misted with 70% food-grade ethanol to ensure proper sanitation.  Allow the ethanol to evaporate before proceeding.  Wineries could also dip the ends in a properly made acidulated-sulfur dioxide mix.  Do not wash off sanitized equipment with a towel or “clean” paper towel.

Always remember that the efficacy of cleaning and sanitation is dependent on the processor to complete this task correctly.  Both cleaning and sanitation should take place immediately before bottling and immediately after bottling is completed.  For more information on proper sanitation techniques, wineries can attend the Penn State Food Safety and Sanitation Short Course, which emphasizes key concepts related to sanitation processes.  This course is also available in online content.

Additionally, the book, Winemaking Problems Solved, has an entire chapter designated to trouble shooting during bottling operations, and is recommended for any winery.

  • Checking sterile filtration integrity

Filter integrity is an easy step that wineries can take to ensure their sterile filtration unit is working properly.  Remember that sterile filtration requires the use of a 0.45 micron (or smaller) absolute filter cartridge.  The Bubble Point Test is an integrity test that should be applied to a filter before and after bottling to ensure filter integrity.

  • Bottle washing

While bottles are sterile when they are formed, many retain cardboard dust (“case dust”) in the bottles by the time they reach the bottling line in the winery, and this acts as a contamination point.  Wineries should also be aware of tiny glass shards that may be retained within the bottle during glass manufacturing.

The best way to remove dust and debris in the bottle is by gas jetting: injecting a small stream of inert gas (e.g. nitrogen) prior to the bottle’s use.

As this is not a sanitation step, it is recommended that bottles also undergo a pre-rinse step with an approved no-rinse sanitizer.  Many wineries utilize an acidulated-sulfur dioxide rinse or ozonated water.

  • Inspecting filled bottles

Many wine microbiology text books recommend sampling one or two filled wine bottles every hour during bottling.  There are several things that wineries can look for including using a microscope to scan for potential contamination, using membrane filtration to enumerate yeast and bacteria on a Petri Dish (pg. 236-238 in Wine Microbiology), or sending samples away to test for bottle sterility.  This quality control step can help minimize worry post-bottling and provide ample feedback regarding bottle efficacy.

Petrifilm that show yeast and mold populations from wine sample.

Petrifilm that show yeast and mold populations from wine sample.

  • Checking sulfur dioxide depletion

The use of sulfur dioxide is the last line of defense in terms of microbial stabilization while wine is in bottle.  Many refermentation incidents are a result of too little free sulfur dioxide in the bottle.

Aeration-Oxidation (AO) system set up to measure free sulfur dioxide.

Aeration-Oxidation (AO) system set up to measure free sulfur dioxide.

During bottling, the wine will lose a little bit of the free sulfur dioxide concentration.  Typically, this is around 10 ppm of free sulfur dioxide concentration, but it will vary from winery to winery, and bottling line to bottling line.  Wineries should sample the sulfur dioxide concentration about 24 hours post bottling to evaluate the average loss of sulfur dioxide during the bottling process.  Extra additions of sulfur dioxide can be made before bottling to compensate for the loss during the bottling process.

Resources & Literature Cited

The Brewers Handbook

Butzke, C. “How long do I need to disinfect my bottling line if my hot water is less than 82°C (180°F)?” in Winemaking Problems Solved

Microbiological Analysis of Grapes and Wine: Techniques and Concepts

Neradt, F. 1982. Sources of reinfections during cold-sterile bottling of wine. Am. J. Enol. Vitic. 33(3):140-144.

Renouf, V., M.-C. Perello, G. de Revel, and A. Lonvaud-Funel. 2007. Survival of wine microorganisms in the bottle during storage. Am. J. Enol. Vitic. 58(3):379-386.

Wine Microbiology

Winemaking Problems Solved


Wine Quality Improvement: Defects

By: Denise M. Gardner

Wine defects happen to all of us. Sometimes I wonder if this is the humbling truth about being a winemaker. Even years of education, training and experience cannot 100% guarantee a perfect aging process after a wine has been bottled. However, a winemaker that understands why wine defects occur, how to prevent them during processing, and how to fix a problematic wine can progressively enhance wine quality more consistently than a winemaker oblivious to the potential of wine defects.

Defects and Quality – Is there a difference?

There are components of wine quality that are completely subjective. If you don’t believe me, you can read a series of comments related to a comment I shared in 2014 to the wine community about embracing both Vitis labrusca and Vitis vinifera wines for what they were to consumers and experts alike.

Wine quality may embrace both a lack of defects present in a given wine in addition to an association with a specific wine style. The stylistic component or whether or not a wine is “true to type” falls into a more subjective category.   Identification of wine defects alone is usually more direct and agreed upon wine tasters. However, I will note that some very interesting wines may also have a defect related to the wine’s flavor profile. For example, many traditional, old-style Rioja wines have associated oxidation flavors, but these wines are still found interesting, and of a particular quality, by consumers and experts. I would say the chance of having a defective wine also considered interesting is more of an “exception” compared to a “general-rule-of-thumb.”

What are common wine defects?

There are several technical wine defects, listed below, that can occur in any wine. Brettanomyces-associated off-flavors, the presence of methoxypyrazines, and flavor presence of potassium sorbate or its breakdown products are more controversial, but often noted by wine experts, critics, and writers. In general, the presence of these components may hinder the perceived quality of your wine, and winemakers should be aware of their controversial nature in the wine community.

Table 1: Summary of Wine Defects and Their Common Descriptors

Table 1: Summary of Wine Defects and Their Common Descriptors

While some defects may be measured analytically at the winery (volatile acidity in terms of acetic acid concentration and high free sulfur dioxide content), most require a winemaker to know the key aroma or taste descriptors sensorily (i.e. smell or taste). In this case, the winemaker is the last line of defense when it comes to identifying wine defects and preserving wine quality. This point emphasizes how important production education and sensory training are when it comes to crafting quality wines.

Where to Find More Information

Luckily, today’s winemakers and cellar personnel have a series of resources beyond your usual text book that are available to improve a winemaker’s ability and skill to identify and remediate defective wines.

1. Attend a wine sensory training workshop: Education is truly a tool for every winemaker. One possible workshop available in Pennsylvania includes the Wine Quality Improvement workshop, held annually in January at Penn State. During this two-day workshop, attendees will address all of the above defects: how to identify, prevent, and remediate them. Additionally, a series of hands-on activities contributes to enhancing each attendee’s identification skills that they can apply directly to their winery operation. If you act now, you may be able to register for the 2015 workshop!

Individual sensory training during the 2012 Wine Quality Improvement workshop at Penn State. Photo taken by Michael Black/Black Sun Photography.

Individual sensory training during the 2012 Wine Quality Improvement workshop at Penn State.

2. Purchase a defects aroma-identification kit: Half of the battle for becoming familiar with wine defects is through continuous exposure to standards that exude the characteristic defect aroma or by tasting wine regularly with someone experienced whom can identify the defective wines for you. This action helps improve one’s “aroma memory.” At the Wine Quality Improvement workshop, we provide each attendee with a take-home wine defects kit to encourage further practice with wine defect aromas after they leave the workshop. However, you can also purchase these kits through Wine Awakenings or Le Nez Du Vin. Additionally, Enartis Vinquiry sells a Wine Defects Kit (product #:10-309-0000) in which concentrated defect aromas can be added to an aromatically neutral base wine for aroma training.

Use of wine defects kits to enhance sensory wine defect identification sills. Photo taken by Michael Black/Black Sun Photography.

Use of wine defects kits to enhance sensory wine defect identification sills. Photo taken by Michael Black/Black Sun Photography.

3. Embrace wine criticism from a wine professional: This can be a tough pill to swallow, as the pride of one winemaker may be disliked by the taster. However, this is truly how winemakers get better at making quality wines within any style or price point. All wine styles – from native, sweet Concord wines to premium age-worthy Cabernet blends – have quality parameters and can be evaluated for defects. Find a professional that has credentials in wine sensory or tasting to discuss your wines for constructive criticism. The best professionals will also be able to direct you in terms of improving your current wines held in tanks and future wines that you will produce. You can also contact your local Extension Enologist for guidance on tastings.

Use feedback on your wines to your advantage. Photo taken by Michael Black/Black Sun Photography.

Use feedback on your wines to your advantage. Photo taken by Michael Black/Black Sun Photography.

4. Contract a wine lab to improve your wines: This thought follows #3, as it is similar in theory. Some wine labs (like Enartis Vinquiry or Virginia Tech’s Enology Service Lab) may offer sensory feedback for a fee. This advice can be helpful, as many of these labs have a panel of individuals taste and evaluate the wine. As tasting abilities vary, having more than one person taste a wine for defect identification can be valuable. (Having multiple people available to taste wine as it goes through production should also be considered in cellar.)

5. Work with winery consultants: Your winery consultant may also be your “wine professional” that identifies problematic wines. That’s okay! While winery consultants come at a fee, the value of winery consultants is that they can improve your production practice to meet your needs while also educating your employees (or yourself) on a one-on-one basis. Luckily, each consultant is unique, and finding one that fits the mentality of your production can put your winery on a successful path for years (or generations) to come.

Alain Razungles, Professor of Enology at the Institute des Hautes Etudes de la Vigne et du Vin. Here he is tasting some eastern U.S. wines and providing feedback to the winemakers in the audience.

Alain Razungles, Professor of Enology at the Institute des Hautes Etudes de la Vigne et du Vin. Here he is tasting some eastern U.S. wines and providing feedback to the winemakers in the audience.

6. Attend defect-based seminars at wine conferences: Many of the local and national wine conferences offer talks on wine defects or other quality issues. The Eastern Winery Exposition, Wineries Unlimited, B.E.V.-NY Conference, PA Winery Association Conference and PA Wine Marketing & Research Board Symposium, and American Society for Enology and Viticulture (ASEV)-Eastern Section Annual Conference are all local options for Pennsylvania producers to attend.

Attending wine conferences and workshops can enhance your wine education. Photo by Michael Black/Black Sun Photography.

Attending wine conferences and workshops can enhance your wine education. Photo by Michael Black/Black Sun Photography.

7. Online guides: Don’t forget to keep reading. Both Penn State and Cornell offer free online publications that can be helpful for beginner and expert winemakers. Penn State’s emerging “Wine Made Easy” fact sheet series has already covered sulfur dioxide and hydrogen sulfide Cornell’s “Cellar Dweller” and enology newsletters also offer a plethora of information pertinent to today’s winemakers.

Getting Ready for Harvest – Part 2: Juice Oxidation

By: Denise M. Gardner

The “Getting Ready for Harvest” seminar featuring José Santos from Enartis Vinquiry (California) included a detailed discussion about the technical aspects of several key processes that are currently of importance to Pennsylvania winemaking.  Some of these topics included:

  • White wine oxidation protection
  • Yeast nutrition and its importance during fermentation
  • Reducing “green” aromas and flavors in red wines
  • Color stability in red wines

In this four part series, I will summarize some of the discussions led by José during the 2014 “Getting Ready for Harvest” workshop.

White Wine Oxidation Protection

There are several ways that winemakers can improve upon current white wine processing operations.  In the past three years, I’ve heard several key discussions on white juice clarity, prevalence of astringent tannins, loss of aromas/flavors essential to the variety, and early onset (i.e. within 1 year of harvest) of white wine oxidation.  While mistakes in the winery can happen, there are various schools of thought that directly address white winemaking and ways to improve upon it.  This summary will discuss the use of antioxidants during pre-fermentation juice settling, and their potential influence on wine quality post-fermentation.

One key topic that José addressed during his seminar was the importance of antioxidant protection in white wine juice.  “Oxidation” and “reduction” are general chemical terms used to describe chemical processes that transfer electrons; oxidation involves the loss of electrons within a chemical species, while reduction results in a gain of electrons for a chemical species.  Typically, many oxidative processes involve the use of oxygen.  Antioxidants, therefore, are chemical species that prevent or inhibit oxidation from occurring.  Generally speaking, wine contains many compounds that can be oxidized, or reduced, although not necessarily all at the same time or within the same chemical pathway.

Currently, most U.S. winemakers add sulfur dioxide (SO2) in the juice phase during settling (i.e. addition of a pectinase enzyme) to inhibit the oxidative browning reaction facilitated by the enzyme polyphenol oxidase (PPO).  Although this is one way winemakers can address white wine oxidation pre-fermentation, many winemaking regions outside of the U.S. have other solutions.

Grape and juice oxidation begins the moment the grape is broken.  For those that utilize mechanical harvesting, oxidation management in wine grapes should be a consideration.  Oxidation can affect many different chemical aspects of juice and wine, including wine color, aroma and flavor development, and tannic stability.  In the worst case scenario grape and juice oxidation can lead to a lack of varietal aroma and flavor, potential development of off-flavors, and a loss of color (for reds) or browning of color (for whites and reds).  Botrytis, a fungal disease that is prevalent in tight-clustered varieties like Pinot Grigio or Pinot Noir and may be more common in wet or humid years, produces laccase, an enzyme that contributes to juice oxidation more efficiently than polyphenol oxidase (PPO).  Additionally, laccase is heat tolerant, which is not the case for PPO, and may continue oxidative processes post-fermentation.

Figure 1: 2008 Chardonnay juice color results after 14 hour treatment with various antioxidants during juice settling (Photo credit: Enartis Vinquiry)

Figure 1: 2008 Chardonnay juice color results after 14 hour treatment with various antioxidants during juice settling (Photo credit: Enartis Vinquiry)

Figure 1 shows the effects of various antioxidants when used in combination with juice settling enzymes.  The control (“without antiox.”) has the darkest associated color.  The sample treated with SO2, however, lacks the amber color associated with PPO activity.  Other samples treated with ascorbic acid or glutathione showed a reduction in the amber color, but not comparable to the SO2 treatment.  However, the treatment with AST addition, a combination of ascorbic acid, SO2, and tannin was capable of inhibiting oxidation to the same degree of SO2 alone.

I know what you’re thinking: What’s the point of using a different product if SO2 gets the job done?

Well, first, I should note that allowing the juice to brown prior to fermentation may not be a bad thing for some varieties.  Non-aromatic varieties, such as Chardonnay, Pinot Grigio, or Cayuga, may benefit from the browning of juice.  This oxidative process will also contribute to oxidizing some phenolics that may otherwise be retained in the wine, and contribute to post-fermentation astringency, which may be undesirable for whites wines.

However, ascorbic acid converts oxygen to hydrogen peroxide 1700x faster than SO2 alone.  For all those wine chemists out there, this sounds like a nightmare because hydrogen peroxide is a very reactive species that does contribute to oxidation.  However, when used in combination with SO2, ascorbic acid can be a powerful tool to utilize the dissolved oxygen available in the juice, and inhibit aromatic oxidation.

Tannins also offer some antioxidant properties.  They can bind to oxygen directly, block enzymatic oxidases (prevent them from working), or inhibit free radicals that contribute to many oxidative processes.

The combination of ascorbic acid, SO2, and tannin acts as an aggressive antioxidant treatment for white juice of aromatic (i.e. Riesling, Vidal Blanc, Gewürztraminer, etc.) varieties, in which the preservation of those aromatics is essential for wine quality.  In this case, the lack of oxidation is also preserving the aromatic compounds from their own oxidative processes.  Enartis’s product, AST (see above), offers this solution.

For those aromatic varieties that may develop a latent astringency, José recommended additionally fining the juice with PVPP or a combination of PVPP and potassium caseinate for high-phenolic varieties.  This treatment should help remove some of those astringent phenolics that are typically more perceptible about 6 months post-fermentation.

It is essential to remember, however, that winemakers should not add ascorbic acid alone.  Due to the fact it does quickly convert oxygen to hydrogen peroxide, generation of hydrogen peroxide alone will constitute more oxidation problems than no antioxidant addition.  The SO2 is needed to quickly scavenge the hydrogen peroxide developed by ascorbic acid.

Practicality in Production

For those using mechanical harvesting the use of antioxidants during harvest time may be a consideration for preservation of aromatics in addition to managing other oxidative processes.  Harvesting should take place during cooler hours of the day in order to slow degradative processes and help protect aroma and flavor compounds that have developed in grape berries.

Pressing White Grapes at Harvest

Pressing White Grapes at Harvest

Racking White Juice

Racking White Juice

Additionally, for those that are receiving grapes or juice from long distances, oxidation should be a concern.  While SO2 provides antioxidant capabilities in the juice, it does not come without consequences.  If grape growers or juice processors are shipping product with a high SO2 content, it may inhibit yeast growth for fermentation.  Furthermore, depending on the variety, some winemakers may prefer no SO2 addition at this stage.  It is essential that growers, processors, shippers, and winemakers work together to determine that the quality of the product upon receiving is well understood.

It is not uncommon to add SO2 to the crusher/destemmer during processing.  Nevertheless, ascorbic acid – SO2 or products like AST, offer alternative solutions for winemakers that are looking to provide antioxidants to white juice.