Practical Brettanomyces Control in the Cellar

By: Thomas J. Payette, Winemaking Consultant

Many winemakers overlook some of the practical control aspects of minimizing Brettanomyces [Brett] growth in their wines.  This article will address some of the items and their circumstances that we should keep in mind while working with our juices and wines.  This article is more a reflection of experience than one jammed with technical data.  It is assumed the reader knows and is aware of Brettanomyces.  To better understand what a Brett microbe might look like please see the author’s portrayal photograph.  This is obviously humor ladies and gentleman to set the stage.

Cleanliness

  No doubt – the first aspect of controlling Brett is cleanliness.  A dirty cellar with poor equipment hygiene will make keeping most bacteria/yeast in the wines in check almost impossible to achieve.  A sound, clean winery will be the assumed premise of this article. Where you take your pomace after pressing should enter your mind in respect to Brett.  Insects from the pomace pile may not just stay at the pomace pile and they may assist in moving brett from the pomace pile to your open bin fermentation vessels or other winemaking contact surfaces, etc

Chemistry

  Most seasoned winemakers realize certain pH levels and free sulfur dioxide levels have limiting affects on many bacteria and spoilage yeasts.  This article will assume the winemaker has his/her finger on the pulse of their wines’ chemistries and understands these chemistry relationships and their influence on the wine.  This article is looking beyond the normal sound winemaking techniques one should already have in place.

Temperature

  Most wine bacteria grow more rapidly at higher temperatures.  If a winemaker keeps their wines stored, after alcoholic and malolactic fermentation, at or near 50 degrees F one will keep most damaging bacteria greatly in check.  It is the author’s understanding Brettanomyces can grow in a free SO2 of 27 ppm when the ambient temperature of the wine is 65 degrees F. The author has greatly used this understanding as a winemaking tool. 

  Often the author will speak with winery owners to negotiate this agreement: “If I can keep the cellar very cold (near 50 degrees F) in the summer months I will trade off little to no heat in the cellar during the winter.”  [This does exclude the lab area that should remain near 68 degrees F for most proper lab functions]  This is in essence a wash financially, in most regions, but a great help to the wines.  

  In practice, on the average, what may happen is the winery may bottom out in the cold months at 40-45 F and near a short-term peak of 65 degrees F during the summer months.  This small upward spike in temp, time wise, is minimal, given the colder months average, which most bacteria, Brett included, have no to little chance to bloom.  It is recommended one use this tool to his / her advantage and the author will often use the colder months after harvest to store his red wines at reasonably low free SO2 values to help soften and evolve the wines during the early months of aging the wine.  By the warmer months, one should bring the free sulfur dioxide level up to that appropriate to combat undesirable microbes.  Try using temperature as your primary tool and if you haven’t built your winery – don’t skimp on cooling!  

When using cold wine storage as your winemaking tool, keep in mind more gases dissolve in cold liquids than warm liquids.  This can be used to an advantage to soften or “micro-ox” some wines but make sure not to exceed what a wine can handle.  Also, understand a wine may evolve slower at lower temperatures since most reactions also slow at lower temperatures.  Wines are no exception to these rules of science.

Racking Timely

  Aging red wines on yeast lees for an extended period of time can be a stylistic tool in a winemaker’s tool box.  Further note these lees may contain unwanted spoilage yeast and microbes from the harvested fruit and/or equipment used to harvest/process the fruit.  If a red wine is stored on its lees it may be more likely to have a Brett bloom since most literature cites certain yeast/Brett populations are greatly reduced by racking the wine off the yeast lees. 

  Research tests on these lees may show active Brett populations that may not have bloomed, just after the yeast alcoholic fermentation.  If there is any doubt as to the condition of the lees, rack early after fermentation to reduce yeast/bacteria-starting loads.

Vacuum Storage

  Many winemakers store and age their cleanly racked red wines in barrel with solid silicone bungs tightly inserted.  Many new cellars have humidity control to help prevent the “angel’s breath” loss of wine from the barrel.  The same cellars may not be very cool especially in caves since the author has noted some caves, on the west coast, to be at between 62 and 65 degrees F without additional cooling.  With additional cooling, one should allow the humidity to drop to a level that evaporation does happen.  Barrels, with a vacuum in them, are less likely to develop spoilage issues due to a sound food science principal that few to no bacteria/yeast can grow in a vacuum. 

  With normal topping of the barrels, say every 4-6 weeks, one will keep most unwanted microbes in check, including brettanomyces. [The author has no data whatsoever that Brett cannot grow in a vacuum – only practical hands on data for this statement.]

Topping Barrels

  As mentioned earlier barrels may be a great aging vessel; yet, many are unclear as to when and how to top.  Topping barrels can be a stylistic tool even down to the frequency of topping.  In relationship to this article, make sure the topping wine for your barrels is Brett free.  One doesn’t want to make the wrong choice of a Brett infected wine source and unknowingly spread that culture throughout the winery spanning a number of barrels.  The author chooses to use similar wine known to be free from Brett of filtered wine, to the proper micron level, that Brett should not be an issue.  Topping, as mentioned in previous articles, can be a major potential source of cross-contamination.

Filtrations

  It is the authors understanding that Brettanomyces yeast has a size range of near 0.80 to 1.1 microns.  With this in mind, we can understand better what size filtrations may be needed to reduce or eliminate the potential of Brett.

  Filtration can be done at anytime during the wines life; but, if successful, with the storage and aging of the wines in the cellar one may just consider the filtration at or near bottling to be the safety net needed as a “just in case” measure. 

  Assuming all malic acid and fermentable sugar have been depleted, one may consider a 0.8 or 0.65 micron absolute pore size filtration.  Care must be taken to keep the pressure down during the filtration step to make sure excess pressure doesn’t allow the yeast to formidably shoulder through the filter media.  In some cases, winemakers and bottling lines have had to use a 0.65 micron rated filter since the 0.8 micron absolute filter can be difficult to obtain at writing of this article.

Summary

  It should be clear to the reader that beyond sound winemaking basics the best and less invasive control of Brettanomyces in fine wine making is temperature.  If winemakers don’t mind roughing it through the winter months, for the sake of the wine, they will be greatly rewarded in the summer months with a lavishly cool cellar. 

  It is highly recommended we all do this in the honor of fine wine making!  For the sake of your wine keep the cellar cool and Brettanomyces should be of little to no concern in your clean wine cellar!

References: 

  Amerine, M.A., Berg, H.W., Cruess,W.V. 1972. The Technology of Wine Making

  Verbal discussion with:  Mr. Jacques Boissenot, Mr. Jacques Recht, Mr. Joachim Hollerith, Mr. Chris Johnson and Mr. Pete Johns.

Short Course:

•   Trade cooling in the summer for limited heat in the winter in the cellar.

•   Let natural barrel vacuum work for you.

•   Filter when needed.

•   Don’t cross-contaminate.

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