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New World Wine Maker Blog - Technical Articles

Skin-fermented white wine – all talk and no action?

When I started writing this blog, an old adage came to mind, “there is more than one way to skin a cat”. If you believe thatthere are many different ways to achieve an objective and that the reason for drinking wine is enjoyment, then skin-fermented wines could be the means to an end.

I tasted skin-fermented white wine (henceforth referred to as orange wine) for the first time in Croatia last year and during that tasting surmised that this type of wine is not for everybody. My second experience with orange wine was last week at a wine tasting chaired by James Pietersen of Wine Cellar (Observatory, Cape Town). During this tasting I was bombarded with so many new (and sometimes weird) aromas, that I soon realised that I was out of my depth. Take a look at Table 1 at the end of this blog for more details.

After the tasting, Edo Heyns (also present at the tasting) and I discussed the wines and he reckoned that this was probably the most difficult tasting that I could have kicked off with (I started at WineLand on 1 February 2017). Edo supplied this quote, “This burgeoning niche category offers some truly delicious wines. Chenin Blanc has particularly risen to the occasion, but there are also impressive blends and Sauvignon Blancs made in this style. The tasting yielded an intriguing list of descriptors and discussions, which is part of the category’s appeal. I specifically enjoyed wines that had a neat balance of texture and acidity. Judging this style definitely tests your tolerance for funkiness. While this is part of the excitement, it could also be its Achilles heel. Skin-fermented wines should first and foremost be good wines. To me, that was not the case for some of the wines in the line-up.”

And judging by how well some of these wines are selling locally, regardless of the relatively higher price, orange wine is doing a lot of well-placed scratching. Speaking of price, these five wines ranged from R135 to R275. While a lot is said about orange wines and their sometimes obvious faults, consider that one of the browner wines at this tasting scored quite well, because of the nose and palate. As it turns out, one cannot solely judge a book by its cover (I’m on a roll with proverbs today …

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Harvest Preparation for Sub-Optimal Fruit: Botrytis

By: Denise M. Gardner

The eastern U.S. growing seasons can be somewhat unpredictable.  Late season rains or untimely hurricane events can be a recipe for disaster for local grape growers, and a few have been unprepared for such events in the past.  These weather events can lead to higher incidences of the grey-rot form of Botrytis in addition to other rots, which may also be related to pest damage.  Furthermore, these weather incidences and pest damage can ultimately impact picking decisions for growers and wineries (Osborne, 2017).

It is almost inevitable that wineries need to be prepared for end-of-season weather flops, and plan for the best possible ways to manage or maintain wine quality in light of above-average disease pressure.

One disease that winemakers can prepare for prior to harvest is Botrytis.  For the purpose of this article, we’ll be using the term Botrytis to indicate the grey-mold or grey-rot form of the disease.  Grey-mold, the form of Botrytismore commonly noticed in humid regions or during heavy-precipitation seasons, can ultimately affect wine quality.  Peynaud (1984) has defined 4 ways in which the grey-mold can negatively affect wine quality:

  • Deplete wine color (especially important in red varieties),
  • Increase the risk of premature browning (through oxidative enzymes),
  • Deplete varietal character (through degradation of grape skins), and
  • Contribution to off-flavors developed by the mold’s presence on the fruit.

Botrytis, grey-mold, infection can force winemakers into alternative winemaking techniques in order to retain wine quality. Photo by: Denise M. Gardner

Based on a 1977 study by Loinger et al., guidelines pertaining to wine quality were developed with regards to a visual assessment of Botrytis incidence on incoming fruit:

  • 5-10% Botrytis rot on clusters: noticeable reduction in wine quality; wine quality is still “good” (as opposed to very good with 0% rot on clusters)
  • 20-40% Botrytis rot on clusters: marked reduction in wine quality; wine quality is “low”
  • >80% Botrytis rot on clusters: wine is commercially unacceptable

With a noticeable sensory and chemical difference in Botrytis-infected clusters, it is best for wineries to develop a standard operating procedure (SOP) for assessing rot-infected fruit, as well as how the grapes should be handled and processed during production.  While there is no one correct way to work with the wine, below are some suggestions or options that wineries can integrate when dealing with Botrytis-infected grapes.  For a full list of possibilities, please visit: http://extension.psu.edu/food/enology/wine-production/producing-wine-with-sub-optimal-fruit/fermenting-with-botrytis-101

Pre-Fermentation Sorting

Some wineries will sort through all incoming grape clusters prior to the crushing/destemming process to assess for any cluster damage or presence of unwanted material.  If your operation is not set up with this equipment, sorting can also take place in the vineyard.  Depending on the concentration of disease and on the projected wine style or quality parameter the fruit will go towards, disease portions of clusters can be cut out in the vineyard.  Or diseased fruit can be left in the vineyard to deal with after the harvest is complete.  Sorting out diseased fruit from that of decent quality will reduce the impact of the mold on the wine’s aroma, flavor, and quality.

Limit Contact Time with Skins

Depending on the resource, there are various recommendations for how to handle diseased fruit.  In whites, some recommend whole cluster pressing and tossing the first 10+ gallons, which are rich in Botrytis metabolites (Fugelsang and Edwards, 2007).  Many recommend separating juice press fractions for white and rosé wines, as this will give the vintner more control over the chemical constituents (e.g., phenolics, enzymes, and disease-related off-flavors) in the final wine.

Depending on the desired outcome for a red wine, treating or limiting skin contact with diseased fruit may be ideal post -primary fermentation.  This would include avoiding extended maceration processes.  Due to the fact that the presence of Botrytis on red varieties reduces anthocyanin and phenolic extraction (Razungles, 2010) in addition to the varietal aromatics, excessive skin contact may not be ideal during primary fermentation.  Whole berry fermentations, as opposed to a more aggressive crush and destem process, may help minimize extraction of Botrytis metabolites, which can also contribute to mouthfeel variations or off-flavors.

Tannin additions pre-fermentation may also be good considerations to compensate for phenolic losses associated with Botrytis infection.  Pre-fermentation and post-fermentation additions may help rebuild the wine’s structure or provide constituents for color stabilization.

Flash pasteurization (i.e., flash détente) has been previously recommended for Botrysized fruit to inactive the laccase enzyme associated with Botrytis, enhance color stability in reds, as well as improve the aromatics and flavors associated with the final wine.  Wines that undergo a thermovinification step tend to extract more anthocyanins and phenolics compared to traditionally fermented wines (Razungles, 2010).  Additionally, this heat step helps to inactivate laccase, which can contribute to early browning or oxidation of young wines.  However, commercial producers may not find this technological application easily accessible.

Therefore, in addition to minimizing skin contact time, winemakers will want to reduce contact time with the gross lees, and may also remove the wine from fine lees associated with the mold-infected fruit quickly.  The integration and use of clean, fresh lees, however, is still encouraged.  Removing the lees associated with mold-infected fruit can help reduce additional contact time with rot metabolites that have settled out with the lees.  This inhibits further integration of those metabolites into the wine.

Inoculate with a Commercial Yeast Strain

The presence of rot is one incidence in which processing techniques (e.g., cold soak) that encourage native microflora to dominate the fermentation are probably not desired.  Things like cold soak and native ferments allow ample opportunity for the mold to progress and contribute to the wine’s flavor.

Fruit that has rot or microflora issues is best inoculated with commercial yeast and malolactic bacteria strains to outcompete the native microflora (including those microorganisms that contribute to the rot), and to give the fermentation its best chance at completing the fermentation cleanly.  Remember that proper yeast nutrition is important to support the yeasts’ growth and to reduce the risk of hydrogen sulfide development.  For more information on determining the starting nitrogen concentrations (YAN) and how to properly treat your fermentation with added nutrients, please refer to:

Penn State Extension’s Wine Made Easy Fact Sheet: Nutrient Management During Fermentation

With high Botrytis concentrations, a more robust yeast strain may be preferred in order to quickly get through primary fermentation.  A quicker fermentation may simplify the aromatics associated with the wine, but it will also ensure little opportunity for additional spoilage.  Saccharomyces bayanus strains are often selected as more robust yeast strains.

Use of commercial yeast strains can be a valuable tool when dealing with disease-infected fruit. Photo by: Denise M. Gardner

Use of Sulfur Dioxide

Sulfur dioxide additions at crush will be determined based on the style of wine in which you are producing (e.g., white, rosé, red, etc.), but in general, the use of sulfur dioxide can help inhibit further spoilage of your product and retain antioxidant capacity.  Sulfur dioxide additions in the juice stage will help minimize early browning, but primarily inactivate PPO.

In general, botrysized wines tend to require more sulfur dioxide as Botrytismetabolites bind with free sulfur dioxide (Goode, 2014).  This is true even when processing wines with the noble rot version of Botrytis.

When primary fermentation, and malolactic fermentation (dependent on style), is complete it is a good idea to ensure that the wine has an adequate free sulfur dioxide content in order to retain its antimicrobial protection.

Fining

Some fining agents may also be applicable in the juice stage.  For example, some producers find it helpful to fine juice with bentonite in order to reduce protein content, as well as help minimize rot-associated off-flavors or partially reduce laccase concentrations.

PVPP can be added to the juice to reduce potential browning pigments or their precursor forms (Van de Water, 1985).

In both of these scenarios, neither bentonite or PVPP is specific for rot-related constituents, but each could be helpful to avoid potential challenges later on in the production process.

The presence of Botrytis can also contribute glucans to the must/wine, which can cause filterability problems for heavily-infected wines.  In this situation, many suppliers have beta-glucanase enzymes that can be applied either to the juice, wine, or both, to help breakdown the glucans and enhance ease of filterability.

A Word about Laccase

Both polyphenol oxidase (PPO) and laccase can cause early browning in grapes and wine.  However, PPO is inhibited by the alcohol content that is developed during primary fermentation.  Laccase, however, is not inhibited by the presence of alcohol, and can only be inactivated by a pasteurization step, heated to at least 60°C (140°F) (Wilker, 2010).

Grapes tend to be higher in laccase concentration when infected with Botrytis, and, thus, wines produced from grapes that had a high incidence rate of Botrytis can develop a brown hue post-primary fermentation.  This oxidative activity can occur even in young wines.

If you are concerned about the prevalence of laccase in diseased-fruit, wineries can submit wine samples to a wine lab for a laccase test.  Or, if you own a copy of “Monitoring the Winemaking Process from Grapes to Wine: Techniques and Concepts” by Patrick Iland et al., pg. 90 and 94 have 2 laccase test protocols that outline how wineries can assess oxidation by laccase.  The results of these test will indicate if extreme treatments are required during production to avoid the rapid and early oxidation caused by laccase.

Literature Cited:

Goode, J. 2014. The Science of Wine: From Vine to Glass. (2nd Ed.) University of California Press: Berkley, California. 216 pg.

Fugelsang, K.C. and C.G. Edwards. 2007. Wine Microbiology: Practical Applications and Proceedings. (2nd Ed.) Springer: New York, NY. 393 pg.

Loinger, C., S. Cohen, N. Dror, and M.J. Berlinger. 1977. Effect of grape cluster rot on wine quality. AJEV. 28(4): 196-199.

Peynaud, E. 1984. Knowing and Making Wine. Wiley-Interscience: New York, NY. 391 pg.

Razungles, A. 2010. Extraction technologies and wine quality. In Managing Wine Quality, Vol. 2 Oenology and Wine Quality. Andrew G. Reynolds, Ed. Woodhead Publishing: Philadelphia, PA. 651 pg.

Van de Water, L. 1985. Fining Agents for Use in Wine. The Wine Lab.

Wilker, K.L. 2010. How should I treat a must from white grapes containing laccase? In Winemaking Problems Solved. CRC Press: Boca Raton, Florida. 398 pg.

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July Pre-Harvest Planning in the Cellar

By: Denise M. Gardner

If you are a wine producer in the northern hemisphere, harvest may feel quite far away.  However, given that it is now the month of July, it will be here before we all know it.

Harvest season is just around the corner! Photo by: Denise M. Gardner

The month of July is a great time to start preparing a few essential pre-harvest tasks including getting a bottling schedule ready, especially if bottling operations have not yet begun, and ordering harvest supplies.   This blog post will focus on these two tasks.

Prepare and Enact a Bottling Schedule

New grapes are about to flood your winery with juice and future wine.  Now is the time to review inventory within the cellar and determine what has to be moved and what has to be bottled before harvest begins.

Freeing up previous years’ inventory by moving it into bottle will free up tank, barrel and storage space for this year’s incoming fruit.  It makes for a much easier transition if all of the wines that need bottling are bottled before harvest season starts.  Bottling during harvest is not only chaotic, but it tires employees, pulls resources from the incoming product, and may lead to harvest decisions that may be regretted later.

Always make sure to get bottled wines properly stored and away from any “wet areas” on the production floor.  If possible, bottled wines should have a separated storage area within an ideal environment that is physically separated from production.  From there, stored wines can be moved into retail space when needed.

For more information on how to get wines prepared for bottling, please visit our previous posts:

Bottling comes with its own set of challenges and risks, but several analytical tests can help put a winemaker’s mind to ease regarding bottle stability. Photo by: Denise M. Gardner

Ordering Fermentation and Lab Supplies

Many suppliers and wine labs offer free shipping in July, which can especially be useful for wineries that are not geographically close to a winery supply store-front.  Planning ahead and determining what fermentation supplies will be needed in August, could save extra money.  Not to mention, having supplies on hand during the busy processing season can be a big stress relief.

Winemakers should also take the time to look at new fermentation products and assess the previous year’s needs in order to adequately supply for the up-and-coming harvest.  Keeping an annual inventory of purchases can be helpful to isolate regular needs.

Things to consider purchasing include:

  • Yeast
  • Fermentation Nutrients
  • Malolactic Bacteria
  • Enzymes
  • Yeast Hulls
  • Salts for Acid Adjustments
  • Tannins
  • Pectic Gums and/or Inactivated Yeast Products
  • Fining Agents
  • Oak Alternatives or Barrels
  • Sanitizing Agents

While new yeasts are released frequently, being constructive about the production’s fermentation needs can help isolate what yeasts are needed for the upcoming harvest.  I typically recommend that all vintners have at least 5 strains on hand for harvest: 2 reliable strains that will get through primary fermentation with little hassle, 1 strain that can be relied upon for sluggish or stuck fermentations, and 2 strains for specialty needs (e.g., sparkling or fruit wine/hard cider production) or experimental use.

Select and purchase your yeast strains in July to take advantage of free-shipping promotions.

Fermentation nutrients should be a must-have for all wineries to help minimize the risk of hydrogen sulfide.  Always double check nutrient requirements for yeast strains purchased.  In general, wineries will need hydration nutrients (e.g., GoFerm), complex nutrients (e.g., Fermaid K), and diammonium phosphate (DAP).

For more information on why YAN is important and how yeasts utilize nitrogen during primary fermentation, please visit the following blog posts:

If you need further step-by-step instructions on how to determine adequate nutrient additions during primary fermentation, please visit our Penn State Extension fact sheet: Wine Made Easy Nutrient Management during Fermentation

Sometimes hydrogen sulfide will arise in a wine by the time primary fermentation ends despite all preventative care.  Making sure there are adequate supplies on hand, such as copper sulfate and PVI/PVP can save time in the future.  Also make plans for ways that the production can reserve fresh lees.  PVI/PVP is a fining agent that can help reduce metals like residual copper, but fresh lees will also help reduce the perception of hydrogen sulfide aroma/flavor and residual copper in the wine.  Having a plan for retaining and storing lees during harvest season can save time during challenging situations that develop through the end of harvest and into the winter’s storage season.  A fact sheet on copper screens and addition trials can be found at the Penn State Extension fact sheet: Wine Made Easy Sulfur-Based Off-Odors in Wine.

I also like to make sure we have supplies on hand in case of heavy disease pressure come harvest.  This includes things like Lysozyme, beta-gluconase, pectinase or other clarification enzymes, and fermentation tannins.  Lysozyme can help reduce lactic acid bacteria levels while beta-gluconase can assist clarification problems associated with Botrysized wines.  For further information on how to manage high-disease pressured fruit, please visit the Penn State Extension website on Fermenting with Botrytis or Managing Sour Rot in the Cellar.

Double check the storage requirements for all materials purchased before and after the product is opened.   It’s important to store all of those supplies in the winery properly as it will ensure their efficacy by the time the product is needed.

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GMO yeast in wine and how to find them

By Erika Szymanski of the Winoscope

The vast majority of wine does not involve genetically modified organisms (GMOs). Let me repeat, the vast majority of wine does not involve GMOs. On to the rest of the story:

Whether wine contains genetically modified organisms (GMOs) is a question I’m asked often. In general, the answer is no. Genetically modified grapevines aren’t being used for commercial winemaking (though not for want of trying). Two genetically modified wine yeasts have crossed the commercial production threshold, but not worldwide. One, the un-charismatically named ECMo01, available only in the United States and Canada, has been engineered to produce an enzyme that degrades urea. That’s a useful property because urea in wine can become ethyl carbamate, which the World Health Organization thinks is probably carcinogenic enough to be worried about it.

The other, ML01 (which rolls off the tongue much more easily), is legal in the US and Canada as well as Moldova, and seems to have won more traction (though not, I dare say, because it’s available in Moldova). ML01 includes genes for two non-Saccharomyces cerevisiae proteins: a malate permease from fellow yeastSchizosaccharomyces pombe, and a malolactic gene from the lactic acid bacteria Oenococcus oeni. Together, those molecules allow ML01 to import malic acid into the cell and convert it into lactic acid, granting ML01 the rather magical ability to perform both alcoholic fermentation and malolactic fermentation simultaneously, all by itself. In addition to speed and convenience, this one-stop fermentation is advertised as a route to fewer wine headaches. Lactic acid bacteria can produce biogenic amines, which can produce headaches and other unpleasantries in sensitive people (I’m one of them); eliminating the need for those bacteria should eliminate the biogenic amines and those symptoms.

For reasons which are probably obvious, North American wineries using these GM yeasts don’t exactly go shouting that news from the rooftops, fewer headaches or not.

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Minimizing Spoilage of Wines in Barrel

By: Denise M. Gardner

The use of oak in the winery offers many options from winemakers.  With today’s availability of various oak products (i.e., chips, staves, powders), winemakers have more choices than ever before to integrate a wood component into their product.  However, the use of oak barrels remains an intrinsic part of most winery operations.  During the aging process, oak barrels have the potential to:

  • integrate new aromas and flavors into the wine.
  • add mouthfeel and/or aromatic complexity to the wine.
  • change the wine’s style.
  • add options and variation for future wine blends.

Additionally, the barrel room is often romantically viewed upon by consumers, and it is not uncommon for visitors to find barrel show cases in many tasting rooms, private tasting rooms, or while on a guided winery tour.

The barrel room at Barboursville Vineyards (VA) gorgeously catches the eyes of their visitors. Photo by: Denise M. Gardner

 

Oak fermenters at Robert Mondavi Winery (CA) that guests can see on their famous guided tour. Photo by: Denise M. Gardner

Nonetheless, barrels also offer challenges to wineries.  One of the most inherent challenges associated with a barrel program is maintaining a sanitation program.

The growth of spoilage yeast, Brettanomyces, is often discussed amongst wineries that utilize barrel aging programs.  However, additional spoilage yeast species such as Candida and Pichia have also been associated as potential contaminants in the interior of wine barrels (Guzzon et al. 2011).  Brettanomyces, commonly abbreviated as Brett, was first isolated from the vineyard in 2006 (Renouf and Lonvaud-Funel 2007) and until that point had most commonly been associated with the use of oak in the winery.  The growth of Brett in wine has the potential to impart several aromas as a result of volatile phenol [especially 4-ethylphenol (4-EP) and 4-ethylguaiacol (4EG)] formation in the wine.  Descriptors used to describe a Bretty wine include: barnyard, horse, leather, tobacco, tar, medicinal, Band-Aid, wet dog, and smoky, amongst others.  It should be noted that the presence of these aromas does not necessarily confirm that Brett is in the wine; there are other microflora, situations (e.g., smoke taint) or oak chars that can impart some of these aromas, as well.

Brettanomyces aroma descriptors. Image by: Denise M. Gardner

When barrels are filled with wine, it’s important to monitor the wine regularly for off-flavors while it is aging.  Wines should be regularly topped up with fresh wine to avoid surface yeast or acetic acid bacteria growth that can contribute to the volatile acidity (VA).  We usually recommend topping barrels up every-other-month.  Keep in mind that free sulfur dioxide concentrations can drop quicker in a barrel compared to a tank or wine bottle (MoreFlavor 2012) and free sulfur dioxide contractions should be checked (in conjunction with the wine’s pH) and altered as necessary to avoid spoilage.  Finally, when using a wine thief, both the internal and external part of the thief need cleaned and sanitized in between its use for each and every barrel to avoid cross contamination.  Dunking and filling the thief in a small bucket filled with cold acidulated water and potassium metabisulfite (acidulated sulfur dioxide solution) is a helpful quick-rinse sanitizer.

Barrels offer a perfect environment for microflora to flourish.  Wine barrels are produced from a natural substance (wood), which has its own inherent microflora from the point of production; obviously, barrels are not a sterile environment when purchased.  However, the structure of wood is rigid and porous, which provides nooks and crevices for yeast and bacteria to harbor within.  The porosity of the wood also makes it difficult to clean and sanitize, especially when compared to cleaning and sanitation recommendations associated with other equipment like stainless steel tanks.  Guzzon et al. (2011) found that barrels used over 3 years in production had a 1-log higher yeast concentration rate retained in the barrel compared to new and unused oak barrels.  This demonstrates the ideal environment within the barrel for retaining microflora over time, even when adequate cleaning and sanitation procedures are utilized in the cellar.

Common barrel sanitizers include ozone (both gas and aqueous), steam, hot water, acidulated sulfur dioxide, and peroxyacetic acid (PAA).  A study conducted by Cornell University on wine barrels used in California wineries found the use of sulfur discs, PAA at a 200 mg/L concentration, steam (5 and 10 minute treatments) to be effective sanitation treatments for wine barrels (Lourdes Alejandra Aguilar Solis et al. 2013).  In this same study (Lourdes Alejandra Aguilar Solis et al. 2013) ozone (1 mg/L at a 5 and 10 minute treatment) was also evaluated and found effective in most barrels tested, but a few barrels that did not show adequate reduction with the ozone treatment.  While the research conducted by Cornell indicated the potential lack of cleaning the barrel thoroughly before the ozone sanitation treatment, Guzzon et al. (2011) cited ozone’s efficacy is most likely caused by its concentration.  Both are important considerations for wineries.

Barrels should always be effectively cleaned of any debris and or tartrate build up before applying a sanitation agent.  This is essential to allow for maximum efficacy during the sanitation step.  High pressure washers, a barrel cleaning nozzle, and the use of steam are some options available to wineries in terms of physically cleaning the interior of barrel.  Additionally, some wineries use sodium carbonate (soda ash) to clean some of the debris (Knox Barrels 2016, MoreFlavor 2012) in addition to the use of a high pressure wash.  Always remember to neutralize the sodium carbonate with an acidulate sulfur dioxide rinse prior to filling with wine.

Dr. Molly Kelly from Virginia Tech University has previously recommended a 3-cycle repeat of a high-pressure cold water rinse, followed by high pressure steam before re-filling a used barrel and assuming the wine that came out of that barrel was not contaminated with spoilage off-flavors (Kelly 2013).  If the barrel is hot by the end of this cycle, it may be advantageous to rinse with a cold, acidulated sulfur dioxide solution before filling the barrel with new wine.  If there isn’t wine available to refill the barrel, it can be stored wet with an acidulated sulfur dioxide solution or using sulfur discs (Kelly 2013).

It is not usually recommended to store used barrels dry for long periods of time, and wineries can use an acidulated sulfur dioxide solution (top off as if it had wine in it) for long-term storage.  However, wineries that store their barrels dry need to rehydrate the barrels prior to filling with wine.  Check the cooperage for leaks, air bubbles, and a good vacuum seal on the bung.  Steam or clean water (hot or cold, overnight) are adequate rehydrating agents (Pambianchi 2002).  Barrels that leak wine offer harboring sites for potential yeast, bacteria, and mold growth, which can all act as contaminants to the wine itself.

It should be noted that contaminated barrels (barrels that produce a wine with off-flavors) may need extra cleaning and sanitation steps to avoid future contamination when the barrel is refilled.  It is typically recommended to discard barrels that have a recorded Brett contamination.  If the barrel has picked up any other off-flavors, especially during storage, it should probably be discarded from future wine fillings.

Barrels undoubtedly offer several challenges for wineries, including proper maintenance, cleaning and sanitation.  Nonetheless, engaging in good standard operating procedures for maintaining the barrel’s cleanliness can help enhance the longevity of the barrel and minimize risk of spoilage for several wine vintages.

 

References

Guzzon, R., G. Widmann, M. Malacarne, T. Nardin, G. Nicolini, and R. Larcher. 2011. Survey of the yeast population inside wine barrels and the effects of certain techniques in preventing microbiological spoilage. Eur. Food Res. Technol. 233:285-291.

Kelly, M. 2013. Winery Sanitation. Presentation at Craft Beverages Unlimited, 2013.

Knox Barrels. 2016. Barrel Maintenance.

de Lourdes Alejandra Aguilar Solis, M., C. Gerling, and R. Worobo. 2013. Sanitation of Wine Cooperage using Five Different Treatment Methods: an In Vivo Study. Appellation Cornell. Vol. 3.

MoreFlavor. 2012. Oak Barrel Care Guide.

Pambianchi, D. 2002. Barrel Care: Techniques. WineMaker Magazine. Feb/Mar 2002 edition.

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

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Carbonation and the pain of Champagne

By Erika Szymanski of The Winoscope

Sparkling wine – or beer, or soda, or seltzer* – triggers an unmistakable set of sensations, addictive or repellent depending on your predilection. But is that sensation a taste? A physical sensation? Something else? Probably some combination of the above, though figuring all of that out is trickier than you might imagine.

First, the bubbles in sparkling wine are carbon dioxide, either the product of yeast fermenting a last little bit of sugar in the bottle or mechanical carbonation with a tank of pressurized gas. Carbon dioxide plus water makes carbonic acid: CO2 + H2O ⇌ H2CO3 . Acids, by definition, are molecules with hydrogens which can and do pop on and off when dissolved in water. If the hydrogens tend to disassociate themselves easily, you’re dealing with a strong acid (e.g. hydrochloric or sulfuric) best used for cleaning glassware or dissolving an inconvenient corpse. If only a small number of hydrogens hop off at any one time, you’re dealing with a weak acid. Carbonic acid, needless to say, is a weak acid, or else seltzer water would be an industrial solvent rather than a cocktail mixer. Chemists were associating the perception of sourness with those free hydrogen ions back at the turn of the twentieth century, but they’re not sufficient to explain sourness alone, and twenty-first century chemists are still trying to work out the remainder. The ongoing search for a complete explanation of sourness is one of those excellent examples of how very simple daily phenomena can end up being unexpectedly complicated when scientists try to explain them in terms of chemistry and biology.

Second, the bubbles in sparkling wine are mechanical stimulation. If you stick your hand into a glass of sparkling water, you’ll feel the “prickle” of bubbles bursting along your skin, and your tongue and the interior of your mouth receives the same sensation. That’s not surprising.

A third component of how we sense carbonation is surprising, or at least it’s surprising to me as a carbonated beverage-lover. Carbonation appears to trigger nociceptors, the specialized receptors we have for sensing pain. Carbonation is, physiologically speaking, irritating.

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