Recent Research: Brett is tougher than we thought
January 06, 2020
The American Journal of Enology and Viticulture published this interesting article from a research group in at the University of Bordeaux in first issue of this year's volume of the journal.
I am not surprised to find that Brettanomyces bruxellensis (Brett) does better, which is to say it is a worse problem, in a warmer cellar. Like any yeast, Brett's metabolism rates tend to correlate to the temperature of the growth medium until things get hot enough to start killing the yeast in question. Brett is notoriously tough, can use a wide range of carbon sources other than sugar, and can grown anaerobically. In addition to sulfur dioxide (SO2), European winermakers are using chitosan of hypobaric (high) pressures to keep Brett populations in check, both of which are recommended by the authors.
I was rather taken aback to find out that a temperature difference as little as four degrees, from 2ºC to 6ºC, is enough to have a detectably larger negative impact on the wine by making volatile phenols, especially the ethyl phenols produced by Brett, appear both earlier and faster, regardless of the wine or the yeast strain present.
The article is specifically targeted at wineries in Bordeaux, but I think it's findings should be as a needed reminder that Brett is more of a potential problem than most of us realise or are willing to admit. I also would like to note that the author's recommendations, specifically to more closely monitor the Brett populations in wines in the cellar during the summer months, and to take more active steps at controlling Brett when needed, as extremely prudent if one does not want to be selling Brett-spoiled wines a couple of years down the road.
Brettanomyces bruxellensis is a spoilage yeast particularly dreaded in red wines, where it produces volatile phenols with sensory properties that lead to wine spoilage. The development of this yeast often occurs during wine aging, especially during the summer. We show that in the Bordeaux region, the temperatures of some cellars rise significantly in July, August, and September. This greatly increases the growth rate of B. bruxellensis strains in both permissive and more unfavorable wines. Therefore, although temperature does not affect the specific formation rate of ethyl phenol, raising the wine temperature from 2 to 6°C makes volatile phenols appear both earlier and faster, regardless of the wine or the yeast strain present. Closer control of active yeast populations and closer monitoring of aging wines is thus essential in the summer, particularly in cellars with poor temperature regulation.