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New World Wine Maker Blog - Technical Articles

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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Brett: The Good, The Bad, and The Ugly

By: Denise M. Gardner

The age-old controversy over the existence of Brettanomyces and its impact on wine quality continues to be a hot button topic in the wine industry.  Many will argue its ability to contribute to style as part of the natural terroir associated with where the grapes were grown.  Others point to the general lack of fruit flavor in Brett-rich wines, and common negligence to winery sanitation.

The truth?

As is the case of many wine production topics, it is likely that the truth lies somewhere in the middle, but the love-hate relationship with Brettanomyceslives on.

What is Brettanomyces (aka Brett)?

Brettanomyces bruxellensis (commonly known as Brett) is a yeast commonly found in wine, which may also be referred to in the wine literature as theDekkera species.  While believed to come from the vineyard, it was first isolated from grapes post-veraison only recently: in 2006 (Renouf and Lonvaud-Funel, 2007).  Brett is also used and found in other fermented beverages including beer, hard cider, and distilled spirits.

In the winery, the use of wood has been identified as a primary source ofBrettanomyces.  In fact, many report that new oak barrels have potential to bring Brett into the winery.  This is significant to wine producers, because it was originally thought that only old, used barrels could provide contamination sources of Brett.

However, knowing that Brett can come into the winery as native microflora to the wine grapes, it is probable to assume that any winery may have Brettpopulations within the production area.  Therefore, it is important for wineries to determine a way to manage Brett during various stages of wine production.

What does Brett do to wine?

Brett yeast typically imparts flavor characteristics to the wine, which can commonly be described using the following descriptors, although others exist:

  • Barnyard
  • Horse
  • Leather
  • Tobacco
  • Tar
  • Medicinal
  • Band-Aid
  • Wet Dog
  • Vomit
  • Plastic or Burnt Plastic
  • Smoky

Brett Aroma

These flavor descriptors are linked to the common generation of 4-ethyl guaiacol (4-EG) and 4-ethyl phenol (4-EP).  In some cases, concentrations of isovaleric acid have also been identified and quantified.  These aromatic/flavor compounds are developed as part of Brett’s metabolism.

Additionally, many winemakers have reported a “metallic bitterness” in the finish of many Brett-infected wines.

Regardless of its exact descriptors, the development of Brett-like flavors often leads to a suppression of the fruit flavors, native to the wine variety.  In many cases where people consider Brettanomyces a flaw, it is due to the fact that there are no residing fruit flavors left in the wine, as Brett tends to mask and dominate the wine flavor.

How does Brett survive in wine?

Brett has the unique ability to “hang out” in the wine until an opportune moment presents itself for growth and proliferation.  Brett can survive in wines, a low pH environment, is tolerant of sulfur dioxide, and does not appear hindered by relatively high concentrations of alcohol (~14%) (Iland et al. 2007).  Additionally, Brett can utilize many substrates thatSaccharomyces yeast (i.e., wine yeast) cannot: malic acid, ethanol, wood sugars, higher levels of fructose, residual amino acids and nitrogen sources.  Therefore, a wine could be considered “dry” (<1.0 g/L residual sugar) and still experience a Brett bloom at some point during its production.

One key problem with Brett is the fact that it often “surfaces” post-bottling (Coulter 2012).  Therefore, if wineries are not conducting adequate analytical and sensory testing pre-bottling, or utilizing proper sterile filtration techniques, they may be bottling a Bretty wine without knowing it!  Coulter (2012) found that it is not unusual for only some bottles within a batch of wine bottled in the same day to have Brett blooms while others do not.  Many note that Brett growth is stimulated by oxygen ingress, and Coulter concluded that the variability associated with the oxygen transfer rate of natural cork closures may contribute to post-bottling variability of Brettblooms.  However, it is important to note that the incidence of Brett growth is not isolated to wines bottled with a natural cork closure.

General Prevention of Brettanomyces in the Winery

It is difficult for wineries to manage Brett once it has surfaced in the winery.  Wineries are encouraged to avoid purchases of old barrels unless they are aware and confident in the seller’s cleaning practices.  Even well-sanitized wineries may harbor Brett populations, and should not be considered risk-free.

Maintaining adequate environmental and equipment sanitation practices is helpful to minimize Brett in the winery.  Many industry members recommend proper barrel sanitation using steam or ozone to prevent or manage Brett.

Despite a winery’s best efforts, Brett is a possibility.  In incidences when there is a Brett bloom in a barrel, it is best to isolate those barrels from others.  Avoid contaminating “clean” barrels or tanks.  Using sterile filtration prior to bottling is recommended for wines that contain Brett to prevent blooms in the bottle.

Winery cleanliness and sanitation is an important component in reducing microbial contamination risks throughout various stages of wine production.  The above image shows an example of good cleaning and sanitation practices.  Photo by: Denise M. Gardner

Winery cleanliness and sanitation is an important component in reducing microbial contamination risks throughout various stages of wine production. The above image shows an example of good cleaning and sanitation practices. Photo by: Denise M. Gardner

References Cited

Coulter, A. 2012. Post-bottling spoilage – who invited Brett? Practical Winery & Vineyard Journal.

Henick-Kling, T., C. Egli, J. Licker, C. Mitrakul, and T.E. Acree. 2000.Brettanomyces in Wine. Presented at: The Fifth International Symposium on Cool Climate Viticulture and Oenology, 16-20 January, 2000 in Melborne, Australia.

Iland, P., P. Grbin, M. Grinbergs, L. Schmidtke, and A. Soden. 2007. Microbiological analysis of grapes and wine: techniques and concepts. ISBN: 978-0-9581695

Renouf, V. and A. Lonvaud-Funnel. 2007. Development of an enrichment medium to detect Dekkera/Brettanomyces bruxellensis, a spoilage wine yeast, on the surface of grape berries. Microbiol. Res. 162(2):154-167.

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Red Wine Aroma & Oxygen Exposure

Published with the permission of NOMACORC. For further information visit www.nomacorc.com

The influence of oxygen on the sensory characteristics of red wine has been long known, since Louis Pasteur observed that, by exposing red wine to air, the astringent character of young red wine was softened, and the bouquet improved. Nowadays, it is generally accepted that a moderate exposure to oxygen can be beneficial for the overall sensory quality of the wines. Insufficient oxygen can prevent softening of mouthfeel characters and favors excessive accumulation of reductive aroma compounds such as hydrogen sulfide and mercaptans, which can be highly detrimental to wine aroma quality. At the same time, excessive exposure to oxygen can cause oxidative spoilage of the wine, with irreversible loss of fruity and floral varietal aromas. Due to this complex response, proper management of oxygen exposure in the winery remains challenging for the modern wine industry, also in consideration to the intrinsic variability of wine characteristics in relation to origin of grapes, vintage, terroir, and winemaking variables.

In consideration of such variability, the main question that winemakers are facing is how much oxygen a wine needs to achieve optimal expression of its sensory potential without showing reduction or oxidation faults. Between production and consumption, wines spend a considerable portion of their life in bottle, particularly in the case of red wine. Therefore, the selection of appropriate packaging solutions is a crucial aspect of wine quality. In particular, as the different closures available on the market have different oxygen barrier properties (a parameter commonly referred to as OTR), selection of closures with the appropriate OTR become a crucial tool for achieving optimal oxygen exposure.

Depending on the materials and technology adopted to produce the closure, OTR can vary to a large extent. Screw cap closures generally offer very low OTRs, due to the minimum amount of oxygen permeating through the liner. Saratin liner have been reported to have an OTR of 0.03 ±0.03mg O2/year (Crochière 2007), while values are slightly higher (but also more inconsistent) in the case of Saranex liners (0.7 ± 0.7mg O2/year) (Crochière 2007). This range of OTR currently available in screw cap liners is therefore relatively limited. Microagglomerated closures are also reported to have relatively low OTR (Lopes et al. 2007), although permeability can vary depending on the producer, and most producers do not give a specific value or have a range of OTR. Therefore, although there is a general tendency to assume similar performances for all closures in this category, some key characteristics can actually vary significantly among different producers. Likewise, the characteristics of synthetic closures can vary depending on the technology of production. Injection molding offers limited possibilities to adjust OTR, while co-extrusion, allows to obtain a broad range of defined OTR, providing winemakers with OTR values that can fit the specific needs of each wine. For example, Nomacorc co-extruded closures offer an OTR as high as 3.5 mg/year (Smart+), down to 1.1 mg/year for the new Select 300. Conversely, natural cork can have extremely variable OTR, due to the intrinsic structural variability of cork itself (Godden et al. 2001). Measures (Lopes et al. 2005 and 2006) under conditions of humidity simulating those occurring in a wine bottle indicate values between 0.05-3.35 mg of oxygen per year even for a very limited sample size. While this variation appears to be extremely large and possibly linked to specific bottling conditions, most authors have reported large variation in OTR for natural closures (Godden et al. 2005, Limmer 2006). At present, it is not possible to put on the market natural cork closures with defined OTR.
Figure 1 shows an example of the potentialities (and difficulties) of closure selection and OTR management to create wines with different sensory profiles. As it can be observed, by exposing the same wine to increasing amounts of oxygen, it is possible to obtain different aroma profiles after 10 months in the bottle. Low oxygen exposure (0.24 mg O2 and 0.57 mg O2 in ten months in 375 mL bottles) resulted in wines exhibiting low intensity of red fruit aromas, and mainly characterized by animal/reduction notes, a feature often observed in Grenache wines matured under reductive conditions. Conversely, increasing oxygen exposure in ten months to 2.4 mg O2 to 3.57 mg O2 allowed better expression of red fruit and caramel aromas, decreasing at the same time the incidence of the animal note. This could be attributed to lower concentration of the aroma compounds involved in the animal notes, allowing expression of fruity aromas.
If we compare this data with the values present in the literature and/or provided by different closure manufacturers, we can deduce that closures such as screw caps allow oxygen exposures in a range close to the profiles obtained at 0.24 and 0.57 mg O2 (blue and red lines), and therefore are more prone to deliver wines with lower fruit expression and higher animal notes. Although these closures can have more consistent OTR than natural corks, they cover a low range of oxygen exposure, not giving to winemakers the option of choosing the degree of oxygen exposure most appropriate for a specific wine. On the other hand, natural cork closures, due to the intrinsic variability of cork composition, can offer a rather broad range of oxygen exposures (even within the same batch of closures), potentially allowing, over a range of bottles of the same wine, either optimal expression of fruit aromas (green line) or dominance of animal notes (blue and red lines). From this point of view, synthetic co-extruded closures (e.g. Nomacorc) closures offer the advantage of a range of different OTR available, allowing winemakers to choose the degree of oxygen exposure most appropriate for their wines.

In spite of its key role in defining the evolution of wine sensory properties during bottle maturation, the value of OTR declared by the manufacturer is not the only key parameter that defines closure performance. Indeed, in order to deliver wines which will evolve in the bottle as the winemaker intended, the consistency of OTR is essential. In practice, once the winemaker has decided the OTR that is most appropriate for his wine(s), this OTR value will have to be rather consistent within single batches as well as across batches, in order to allow uniform aging. Figure 2 shows the variation in OTR values (expressed as %CV over 5 closures of the same batch) of different inner seal closure types, as obtained from measures with fluorescence method (Diéval et al. 2011). In agreement with Brotto et al. (2010), synthetic closures, in particular extruded products, show very low CV%, reflecting the intrinsic nature of the manufacturing process, which allows a high degree of control of production variables. Higher %CV were observed for natural cork-based products, consistent with the relatively unpredictable characteristics of the raw material. The high variations observed were often due to leakage, which in some cases made the measure impossible (labelled as leakage (L) on all closures).
In conclusion, understanding the influence of OTR on wine sensory quality allows to deliver wines which will reflect, upon consumption, the intention of the winemaker. Availability of a range of OTRs values, as well as consistency of those values across different batches, are key factors to succesful implementation of oxygen management strategies focused on closure selection.
Suggested readings

Brotto, L.; Battidtutta, F.; Tat, L.; Comuzzo, P; Zironi, R. Modified nondestructive colorimetric method to evaluate the variability of oxygen diffusion rate through wine bottle closures. J. Agric. Food Chem., 58, 3567–3572, 2010
 Crochière GK. Measuring oxygen ingress during bottling/storage. Practical Winery & Vineyard, January/February: 74–80. 2007.
Diéval, J-B., Vidal, S., Aagaard, O. Measurement of the oxygen transmission rate of co-extruded wine bottle closures using a luminescence-based technique. Packag. Technol. Sci., 24: 375–385, 2011. 
 Godden, P.; Francis, L.; Field, J.; Gishen, M.; Coulter, A.; Valente, P.; Hoj, P.; Robinson, E Wine bottle closures: physical characteristics and effect on composition and sensory properties of a Semillon wine. 1. Performance up to 20 months post-bottling. Aust. J. Grape Wine Res. 7, 64-105, 2001
Godden, P.; Lattey, K.; Francis, L.; Gishen, M.; Cowey, G.; Holdstock, M.; Robinson, E.; Waters, E.; Skouroumounis, G.; Sefton, M.; Capone, D.; Kwiatkowski, M.; Field, J.; Coulter, A.; D’Costa, N.; Bramley, B. Towards offering wine to the consumer in optimal condition – the wine, the closures and other packaging variables: a review of AWRI research examining the changes that occur in wine after bottling. Wine Ind. J., 20, 20-30, 2005
Limmer, A. The ‘permeability’ of closures. Austr. NZ Grapegr. Winem., 106-111, 2006
 Lopes, P.; Saucier, C.; Glories, Y. Nondestructive colorimetric method to determine the oxygen diffusion rate through closures used in winemaking. J. Agric. Food Chem., 53, 6967–6973, 2005
Lopes, P.; Saucier, C.; Teissedre, P. L.; Glories, Y. Impact of storage position on oxygen ingress through different closures into wine bottles. J. Agric. Food Chem., 54, 6741–6746, 2006
Lopes, P.; Saucier, C.; Teissedre, P. L.; Glories, Y. Main routes of oxygen ingress through different closures into wine bottles. J. Agric. Food Chem., 55, 5167–5170, 2007

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