Lab results in 7 days is too late!

Wine aging a critical period for Brettanomyces yeasts growth

Why winemakers cannot afford to wait seven days lab results.
winemaker angry to wait 7 days for results as situation is criticial
Nobody can afford to wait 7 days for lab results to monitor Brett growth risk in red wines!!

Why waiting 7 days for the result of the agar plates, favors the growth of Brettanomyces bruxellensis and volatile phenols in the wine?

After the alcoholic and malolactic fermentation of red wine, a critical period begins for red wine, including some white wines aged on lees.

During this critical period, winemakers must avoid at all costs any spontaneous growth of Brettanomyces bruxellensis (Bretts) yeasts.

To control the development of these Bretts in the wine, one must wait 7 days to obtain the results of the agar plates, a critical period favorable to the growth of Bretts and the increase of volatile phenols in the wine.

In the meantime, the Bretts can multiply and reach critical thresholds of volatile phenols production making the contaminated wines unfit for consumption. This results in financial losses for the world wine market estimated at millions of euros per year.

Therefore, for many years, winemakers have been looking for a simple and reliable technology for the rapid on-site detection of viable Bretts.

Winemakers no longer want to wait more than 7 days for the results of culture media to know if the wine is contaminated with viable Bretts.

But how do Bretts contaminate red wine?


Meanwhile exponential growth Brettanomyces increase wine ethylphenols.
meanwhile within 7 days Bretts increase exponentially
In the meantime, Brettanomyces develop and can reach critical thresholds of ethylphenol production.

Brettanomyces are spoiling red wines, by converting ethylphenols precursors , as p-coumaric acid or ferrulic acid into 4-Ethylphenol (4-EP) together with 4-Ethylguaiacol  (4-EG) volatiles by-products..

These precursors are present naturally in sufficient amount in all red wine grape species, except Pinot noir.

  • When the phenol derivate 4-EP reaches the sensory threshold> 430 μg / L , it is perceptible and gives organoleptic defects to the wine. High 4-EP content is associated with odors of stable, bandage or mouse taste.
  • When the phenol derivative 4-EG reaches a critical threshold > 100 µg / L, it contributes to give the red wine odors of spices, or clove.


coumaric acid converstion to 4-ethylpenol

4-EP is produced from the precursor p-coumaric acid. Brettanomyces converts this to 4-vinylphenol via the enzyme cinnamate decarboxylase. 4-Vinylphenol is further reduced to 4-ethylphenol by the enzyme vinyl phenol reductase.

Undrinkable phenolic wines cause of important financial losses
A Brett contaminated red wine can give off very smells of horse sweat, barnyard, bandages, smoke or cloves, or give a mousy taste.
bad wine smell and taste
Very unpleasant odors emanate from a phenolated wine, rendering it undrinkable.
Increase in volatile phenols as a function of the population of Brettanomyces bruxellensis/ml of wine source: Brettanomyces bruxellensis: the current state of play Aline Lonvaud-Funel IVES

But how to avoid the increase of these phenol derivates, before it is too late? It all begins by monitoring the yeast flora during wine aging.

Monitoring the wine aging microflora to prevent Bretts growth.

During the wine aging stage in barrels, regular wine racking of wine lees normally reduces viable yeast populations.

Normally there should be no yeast flora regrowth,

Therefore, any abnormal yeast growth at this stage in wine lees indicates an undesirable Brettanomyces yeast growth (symbolized on the right graph by a on dashed line).

Thus, this undesirable growth of Brettanomyces bruxellensis presents a high risk of alteration of the red wine by the production of ethyl-phenols.

Wine biomass evolution before and after malolactic fermentation of red wine

But where and why are Brettanomyces most likely to develop during wine aging?

Wine lees favorable to Brettanomyces growth during wine aging

During wine aging following sulfur addition, vast majority of viable yeast population  in bottom wine lees are Brettanomyces yeasts.

As Saccharomyces and other aerobic yeasts prefer the oxydizing wine environment of the yeast veil on wine surface, to the opposite Brettanomyces thrive in the anaerobic environment of wine lees.

Meanwhile wine aging progress, regular wine lees racking, are normaly reducing viable yeast counts, and any abnormal yeast growth at that stage in  wine lees indicates an undesirable Bretts yeast growth  with a high red wine spoilage risk.

Production of volatiles ethylphenols, by Brettanomyces are the major wine spoilage risks of red wine producers.

Climate change impact red winemaking  increases pH levels, and inactivates free sulfur dioxide present in wine, increasing possibility of lactic acid bacteria and Brettanomyces growth. Even Pinot noir wines are at risk with climate change to develop volatile ethylphenols, although Pinot noir grapes have low ferrulic acid & p-coumaric acid  amounts. See why ?

Pinot Noir now at risks for ethylphenol spoilage with climate change.
Spoiled Brett wines equals wine value loss
Volatile phenolic compounds in red wine, are responsible for millions of dollars of losses per year for winemakers around the world. More climate change will increase, the more this wine spoilage will increase.

With increased temperature, red wine sugar concentration increases together with wine pH. In turn higher wine pH inactivates free sulfur dioxide, giving a regrowth opportunity to lactic acid bacteria (Lab) like oenoccoccus oeni, and to Brettanomyces.


Some of these lactic acid bacteria, have ability to convert coutaric acid (in sufficient amount in Pinot Noir) into p-coumaric acid, giving extra ethylphenol precursors to the Bretts yeast population  of Pinot noir wine aging wine.

Therefore Pinot noir have risks also to be spoiled by Brettanomyces wine off-flavors, with risks of financial loss. Therefore the time when Burgundy winemakers did not worry about  Brettanomyces yeasts growth in their red wines is now over.

Lactic acid bacteria contribution to volatile phenolic compounds in pinot noir .

Some of these lactic acid bacteria have the ability to convert coutaric acid (in sufficient quantities in pinot noir) into p-coumaric acid. Thus, these bacteria give additional precursors of ethyl-phenols to the Bretts yeast population present in pinot noir during aging. In this way, the Bretts have everything they need to produce the volatiles phenolic compounds that alter pinot noir.

Since waiting for the results of agar plates to count viable Bretts can be catastrophic for a winemaker, are rapid methods of analyzing Brettanomyces in wine reliable as an early warning tool?

Do rapid methods such as PCR (Polymerase Chain Reaction) give reliable results? To find out, read our next article by clicking on the button below.

Are they not rapid methods, which alert winemakers on Brettanomyces growth in wines?

Since waiting for the results of agar plates to count viable Bretts can be catastrophic for a winemaker, are rapid methods of analyzing Brettanomyces in wine reliable as an early warning tool?

Do rapid methods such as PCR (Polymerase Chain Reaction) give reliable results? To find out, read our next article by clicking on the button below.

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