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New World Wine Maker Blog - Technical Articles

Taking the Water Out of Winemaking

A biotech innovator develops a new way to lower costs for small wineries and reduce water usage across the industry

A biochemical engineer by training, Vijay Singh spent decades working with pharmaceutical industry bioreactors in New Jersey. When he retired early, he decided to experiment with home winemaking. He quickly learned that winemaking requires extensive manual labor, scrubbing and washing. Quality wine demands spotless tanks, pumps, hoses and floors, and all of that demands a lot of water.

“I’m quite lazy. I don’t like to do things that are just tedious,” said Singh, laughing. He asked himself: What if a winery could reduce the time and effort devoted to those tasks—and conserve water simultaneously?

His answer has led to a new product, in trial this harvest at more than 15 wineries in the United States and Spain. Called GOfermentor, it involves fermenting wine in a disposable plastic bag. The device aims to make it easier for small winemakers to get started and help large producers make small lots, while dramatically cutting back water use in the process.

One of the more than 20 patents Singh developed during his career is the Wave Bioreactor, which replaced hard-to-sterilize tanks and stirrers for mixing vaccines, antibodies and other cell cultures with disposable plastic bags on rocking platforms.

GOfermentor builds on that idea of trading vats for portable and disposable components. The device consists of a reusable rigid base; a control panel for monitoring temperatures, logging data and scheduling punch-downs; and a single-use, flexible, biodegradable plastic liner for either a 1-ton or 2-ton batch.

The liner has two completely separate chambers—after harvest, rather than dumping crushed grapes into a vat, the winemaker places them into a chemically inert chamber. During red wine fermentation, carbon dioxide pushes skins and other solids up to form a cap atop the juice. Winemakers usually punch the cap down or pump the juice over the cap to break it up and submerge the solids.

To replace manual punch-downs, the GOfermentor gradually inflates the liner’s second chamber, a blue nylon bag. As it expands, the CO2 in the fermentation chamber is vented, the liquid is pushed up through the cap and that cap is squeezed, breaking it up. The bag is then deflated, and the chunks of wet skins settle back into the liquid.

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New technology for juice recovery in winemaking

by Loftie Ellis, Hand Perabo & Brett Rightford

Decanter technology can have a huge impact on juice recovery in future, according to results of commercial-scale tests.

Standard practices for the processing of grapes to juice include destemming, crushing, draining, pressing and settling or flotation. The result is always two fractions of juice: higher-quality free-run juice and lesser-quality press juice. New developments in decanter technology allow separation of juice, either directly after removal of the stems, or after some contact time. The juice is recovered without draining and/or pressing and the processing is continuous.

Worldwide, decanters are commonly used on many different products to remove solids from liquids. When the use of the Hiller decanter was first considered for commercial-scale grape processing, the idea was met with great resistance (especially from Germany). Yield and the quality of the juice obtained were the main concerns. After trialling the Hiller decanter for the past five vintages in South Africa, it can be concluded that it has the possibility of making a significant contribution to process optimisation in wineries. This article reports on three of the trials conducted in the past five years.

Materials and methods

The Hiller decanter used in the trials was a small unit, capable of processing 10 tonnes of grapes per hour. The grapes entered the system either destemmed and crushed, or destemmed and uncrushed. Separation of juice and solids happened within minutes. The pomace, mainly grape skins and pips, contained less than 50 ℓ of juice per tonne of grapes.

Trials were performed with Sauvignon Blanc and Chardonnay at Groote Post; Sauvignon Blanc at Boschendal; and Chardonnay and Pinot Noir for the production of Méthode Cap Classique (MCC) sparkling wine at Graham Beck, Robertson.

Analyses performed on both decanter and control juice and the resulting wines included: juice yield, total phenols, pH, titratable acidity (TA), potassium concentration, as well as informal sensory evaluations of the final wines. The analyses were performed by Wine Quality Consultants and Vinlab.

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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!

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Stabilizing Wines in the Cellar

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, 2ndedition. 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

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Understanding Wine Lees!

Reproduced with permission from the Dept of Food Science & Technology, Virginia Tech

The Nature of Wine Lees
During aging sur lie, yeast components are released into the wine. These macromolecules can positively influence structural integration, phenols (including tannins), body, aroma, oxygen buffering, and wine stability. Some macromolecules can provide a sense of sweetness as a result of bridging the sensory sensations between the phenolic elements, acidity, and alcohol, aiding in harmony and integration.
Mannoproteins in the yeast cell wall are bound to glucans (glucose polymers), which exist in wines as polysaccharide and protein moieties (Feuillat, 2003). They are released from the yeast cell wall by the action of an enzyme, β-1,3-glucanase. β-1,3-glucanase is active during yeast growth (fermentation) and during aging in the presence of non-multiplying yeast cells. Stirring increases the concentration (Feuillat, 1998).
Lees and mannoproteins can impact the following:

integration of mouthfeel elements by interaction between structural/textural features
reduction in the perception of astringency and bitterness (Escot et al., 2001; Saucier, 1997)
increasing wine body
encouraging the growth of malolactic bacteria and, possibly, yeasts
preventing bitartrate instability (Lubbers et al., 1993; Moine-Ledoux, 1996; Moine-Ledoux and Dubourdieu, 2002; Waters et al., 1994)
interacting with wine aroma (Lubbers et al., 1994)

The amount of mannoprotein released during fermentation is dependent on several factors, including the following:

Yeast strain: Large differences are noted among yeasts in the amount of mannoproteins produced during fermentation and released during autolysis.
Must turbidity: Generally, the more turbid the must, the lower the mannoprotein concentration (Guilloux-Benatier et al., 1995). Mannoproteins released during fermentation are more reactive than those released during the yeast autolysis process in modifying astringency. This helps provide additional justification for measuring the non-soluble solids of juice pre-fermentation.

Wines aged on lees with no fining have mannoproteins present, while those fined prior to aging have a large percentage of mannoproteins removed. Periodic stirring sur lie increases the mannoprotein concentration, and increases the rate of β-1,3-glucanase activity. Generally, yeast autolysis is relatively slow (in the absence of glucanase enzyme addition) and may require months or years to occur, limiting the mannoprotein concentration (Charpentier and Feuillat, 1993).
The impact of lees components such as polysaccharides on astringency can cause an increase in the wine’s volume or body. Lees contact is particularly effective at modifying wood tannin astringency by binding with free ellagic tannins (harsh tannins). Sur lie storage can reduce the free ellagic acid by as much as 60% (via precipitation), while increasing the percentage of ellagic tannins bound to polysaccharides by 24% (Ribéreau-Gayon et al., 2000).
In the Burgundy and other regions, red wines are aged on their lees in conjunction with the addition of exogenous β ‑1,3-glucanase enzyme. This procedure is an attempt to release mannoproteins, which winemakers believe may enhance the suppleness of the wine, while reducing the perceived astringency.
Several alternative methods of increasing mannoprotein levels have been suggested (Feuillat, 2003), including the following:

selection and use of yeast which produce high levels of mannoproteins during the alcoholic fermentation
yeast which autolyze rapidly upon completion of alcoholic fermentation
addition of β-1,3-glucanase to wines stored on lees
addition of exogenous mannoproteins (proprietary products), prepared from yeast cell walls, to wines on lees

Lees Management Considerations.
Table 1 shows some important practical winemaking considerations regarding lees management.
During fermentation, the level of macromolecules continually rises, peaking at approximately 270 mg/L, by which time they contain 82% sugar and only 18% protein (Feuillat, 2003).
Guilloux‑Benatier et al. (1995) found a relationship between the degrees of must clarification and the amount of yeast macromolecules recovered in the wine. When the must was not clarified, there is no production of yeast macromolecules.
Table 1Lees Management Considerations

Non-soluble solids level

Method of stirring

Frequency and duration of stirring

Type and size of vessel

Duration of lees contact

MLF

Timing and type of racking

SO2 timing and level of addition

Frequency of barrel topping

However, mild must clarification, such as cooling for 12 hours, increased the amount of yeast-produced macromolecule production by 76 mg/L, and heavy must clarification, such as bentonite fining, increased the production by 164 mg/L. Boivin et al. (1998) found that the amount of macromolecules produced will vary between 230 and 630 mg/L, and that they will contain 20 – 30% glucose and 70 – 80% mannose.
During lees contact, the composition of the wine changes as the yeast commence enzymatic hydrolysis of their cellular contents. One important feature is the process of proteolysis, whereby proteins are hydrolyzed to amino acids and peptides. These compounds result in an increase in the available nitrogen content of the wine. Amino acids can act as flavor precursors, possibly enhancing wine complexity and quality.
Yeast-derived macromolecules provide a sense of sweetness as a result of binding with wood phenols and organic acids, aiding in the harmony of a wine’s structural elements by softening tannins.
It is important to differentiate between light lees and heavy lees. Heavy lees can be defined as the lees which precipitate within 24 hours immediately post-fermentation. They are composed of large particles (greater than 100 micrometers) and consist of grape particulates, agglomerates of tartrate crystals, yeasts, bacteria, and protein-polysaccharide-tannin complexes.
Light lees, on the other hand, can be defined as those that precipitate from the wine more than 24 hours post-fermentation. These are composed mainly of small particles (1- 25 micrometers) of yeasts, bacteria, tartaric acid, protein-tannin complexes, and some polysaccharides.
There is no value in storing wine on heavy lees. Indeed, such storage can result in off aroma and flavors, and a depletion of sulfur dioxide. Light lees storage, however, can have a significant advantage in structural balance, complexity, and stability.
Lees stirring and the frequency of stirring is important, both as a practical and stylistic consideration. Feuillat and Charpentier (1998) have demonstrated that periodic stirring of the wine while on lees increases the mannoprotein level and the amount of yeast-derived amino acids, and that wines aged on their lees in barrel exhibit an increase in colloidal macromolecules.
Stirring generates an oxidative process which increases the acetaldehyde content, and which may increase the acetic acid concentration. Stirring also changes the sensory balance between fruit, yeast, and wood by enhancing the yeast component, and reducing the fruit and, to a lesser degree, the wood component.
Additionally, stirring may have the effect of enhancing secondary chemical reactions, possibly as the result of oxygen pick-up. Stuckey et al. (1991) demonstrated increases in both the total amino acid content and wine sensory score in wines stored for five months without stirring. The non-stirred wine was perceived to have greater fruit intensity.
MLF reduces the harshness of new oak and aids in the development of complex and mature flavors. Traditionally, stirring is continued until MLF is complete. After that, the lees are said to become more dense, which aids in clarification.
During barrel aging, what we are looking for is slow, well-managed, and controlled oxygenation. Some lees contact may allow for this oxygenation, and lees aid in the prevention of oxidation.
In Burgundy, wines are traditionally racked off the lees in March, usually the time when MLF is completed. Frequently this is an aerobic racking off the heavy lees, then back into wood on light lees, followed by an SO2 addition. Leaving the wine on the light lees helps to nourish the wine. The addition of SO2 helps to protect the wine from oxidation. A subsequent racking often occurs in early July, and is in the absence of air.
Timing of SO2 additions, and the quantity of SO2 added, are important stylistic considerations. Early use of SO2 increases the number of components that bind to subsequent additions of SO2. The addition of too much SO2 counters the wood flavors and limits oxidation reactions, while too little SO2 may allow the wine to become tired and over-aged.
Production considerations, such as the timing of MLF, the method of barrel storage, and time of bottling, are factors influencing SO2 levels. Barrel topping is an aerobic process that can result in excessive oxidation. Additionally, wines that spend a second winter in the cellar tend to lose their aroma unless the wine is particularly rich.
Delteil (2002) compared two red wines. One wine was barrel-stored on light lees for 9 months; the other, racked several times prior to barreling, was stored for the same period without lees. These two Syrah wines differed significantly in their palate and aroma profiles.
The wine stored sur lie had a much lower perception of astringency and a greater integration of the phenolic elements. The sur lie wine also had a lower perception of oak character, resulting in a higher perception of varietal fruit.
Lees contact is particularly effective at modifying wood tannin astringency by binding with free ellagic tannins, thus lowering the proportion of active tannins. Sur lie storage can reduce the free ellagic acid by as much as 60%, while increasing the percentage of ellagic tannins bound to polysaccharides by 24% (Ribéreau-Gayon et al., 2000).
The following is a review of the impact of lees on wines.

Lees, Color and Mouthfeel.High lees concentration can reduce color, as a function of adsorption onto the yeast cell surface.  Additionally, lees adsorb oxygen which can limit the anthocyanin-tannin polymerization, resulting in an increase in dry tannin perception. This may or may not be off-set by the release of lees components which can soften mouthfeel.

Lees and Wine Aroma. Aroma stabilization is dependent upon the hydrophobicity (ability to repel water molecules) of the aroma compounds. The protein component of the mannoprotein fraction is important for overall aroma stabilization (Lubbers et al., 1994). Such interactions can modify the volatility and aromatic intensity of wines.

When wine is aged on its lees with no fining, mannoproteins are present and are free to interact and to fortify the existing aroma components. When wines are fined prior to aging, mannoproteins are removed and will not be present to augment the existing aroma components. Additionally, when wines are cross‑flow filtered, eliminating a certain percentage of macromolecules, the loss of color intensity, aroma, and flavor can be noted.

Lees and Oak Bouquet. Lees modify oaky aromas, due to their ability to bind with wood-derived compounds such as vanillin, furfural, and methyl-octalactones.

Lees and Oxidative Buffering Capacity. Both lees and tannins act as reducing agents. During aging, lees release certain highly-reductive substances which limit wood-induced oxygenation. Wines have a higher oxidation-reduction potential in barrels than in tanks. Inside the barrel, this potential diminishes from the wine surface to the lees. Stirring helps to raise this potential.

This is a primary reason why wines stored in high-volume tanks should not be stored on their lees. Such storage can cause the release of “reductive” or sulfur-containing compounds. If there is a desire to store dry wines in tanks sur lie, it is recommended that the lees be stored in barrels for several months, then added back to the tank (Ribéreau-Gayon et al., 2000).

Lees and White Wine Protein Stability. The greater the lees contact, the lower the need for bentonite or other fining agents for protein stability. It is not believed that lees hydrolyze grape proteins, or that proteins are adsorbed by yeast. Rather, lees aging produces an additional mannoprotein, which somehow adds stability. The production of this mannoprotein is increased with temperature, time, and frequency of stirring.

Lees and Biological Stability. Guilloux‑Benatier et al. (2001) have studied the liberation of amino acids and glucose during barrel aging of Burgundy wine on its lees. Their studies were done with and without the addition of exogenous β‑1,3-glucanase preparations. They found little or no increase in amino acids in wine stored on lees, versus wine stored on lees with the addition of β‑1,3-glucanase.

Their most significant finding was an increase in glucose concentration, from 43 mg/L in the control wine, to 570 mg/L in wine stored on its lees, to 910 mg/L in wine stored on its lees with added β ‑1,3-glucanase. The finding of this relatively large amount of glucose led these authors to speculate that the growth of the spoilage yeast Brettanomycesin barreled wine may be stimulated by the availability of this carbon source.

Lees and Bitartrate Stability. Mannoproteins produced by yeast can act as crystalline inhibitors. The longer the lees contact time, the greater is the likelihood of potassium bitartrate stability.

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How quickly does oxygen disappear from white wine?

by Wessel du Toit, Daniella Fracassetti, Carien Coetzee, Andreja Vanzo & Davide Ballabio – for Wineland Magazine

Introduction

Oxygen plays an important role in wine production. The exposure of red wines to small amounts of oxygen can be beneficial to the wine’s development in terms of colour stability and the softening of tannins during barrel ageing. However, in general the addition of oxygen in white wine is not wanted. This is due to the development of a brown colour, a decrease in fruitiness in the wines and an increase in acetaldehyde levels. Factors affecting the consumption of oxygen in white wines are not completely clear, which is probably due to the large chemical differences existing between white wines from different cultivars, areas and vintages. The main aim of this work was thus to follow the decrease in dissolved oxygen concentrations in a number of white wines and to try to link these with the chemical composition of the wines.

Materials and methods

We obtained 13 young Sauvignon blanc wines from the 2010 vintage just after the completion of alcoholic fermentation. These wines were collected from different commercial wineries before any SO2 additions were made after alcoholic fermentation and transported to the Department of Viticulture and Oenology, Stellenbosch University. The wines were collected in 20 ℓ canisters into which N2 gas had been previously blown. The pH of these wines ranged from 3.2 to 3.5 with alcohol levels ranging from 12.3% to 13% v/v. Each wine was then divided into two treatments, one that received no SO2 addition, with the other half receiving 30 mg/ℓ SO2. All the wines were then saturated with oxygen and the wines placed at 37°C for 60 days to enhance the oxidation process. Oxygen levels were monitored daily during this period and wine samples drawn at the beginning and end of the experiment for chemical analyses. Analyses included free and total SO2, glutathione (GSH) analyses, oxidised GSH, grape reaction product, range of phenolic compounds such as caffeic acid, caftaric acid, catechin, coumaric acid, ferulic acid etc., Cu, Fe, as well as absorbencies at 280 nm (total phenolics) and 420 and 440 nm (brown and yellow colour).

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