Ecologie et Origine de Brettanomyces dans les vins

Ecology and Origin of Brettanomyces in wines

Brettanomyces : Yesterday's Myths and Today's Realities
Ecology and Origin of Brettanomyces in wines
This saga is divided into 6 articles
Read the introduction
Brettanomyces is a yeast that has been known for a long time but has recently attracted a lot of attention. The latest fashionable subject, controversies, myths, miracle solutions are now legion and contribute to enormously complicating a serious problem but nonetheless not as complex as some would have us believe... The abundance of information of varying quality on this subject has rather detrimental to the management and solution of the problem Brettanomyces in red wines. The main objective of this article is to take stock of the key elements likely to significantly influence the development of microorganisms in wines and to identify practical and effective tools for controlling their development.
Brettanomyces (sporulating form Dekkera ) is a yeast initially identified in beer by Claussen (1905)[1] then in fermenting musts (Kufferath, 1921)[2] and finally in wines by Custer (1940) then by Peynaud and Domercq (1956) [3]. This yeast, which belongs to the family of Saccharomycetaceae (as Saccharomyces ) exists in wines primarily across species bruxellensis . It was initially described as troublesome because of its capacity to refermentate sweet wines and interfere with alcoholic fermentation by Saccharomyces sp . most often forming large quantities of acetic acid.
In fact, if this type of problem does indeed exist with Brettanomyces in winemaking, the clearly more frequent and potentially more bothersome alteration is quite different. Indeed, this yeast is capable of decarboxylating cinnamic acids naturally present in grapes and wine (cinnamic acid p -coumaric, ferulic and caffeic) into vinyl-phenols and then reducing them to ethyl-phenols (mainly 4-ethyl-phenol, 4-ethyl-guaiacol and incidentally 4-ethyl-catechol) which accumulate. These volatile and odorous molecules are very stable and give the wines a very characteristic “phenolic” aroma which was ultimately called “Brett” character.
The content of ethyl phenol precursors is never a limiting factor, all wines (and grape juices) contain sufficient acid p -coumaric acid (the most abundant cinnamic acid) to produce several milligrams of 4-ethyl-phenol per liter of wine!
After several years of useless controversies, with a variable capacity depending on the strains, we demonstrated [4] that only Brettanomyces was capable of forming in red wines the high quantities of ethyl phenols at the origin of the “Brett” character.
The “phenolic” or “Brett” character is relatively common in red wines and seriously affects the varietal aromatic typicity. It is in this and mainly (not to write only) that Brettanomyces represents a serious problem in oenology. Indeed, if we allowed the wines to evolve naturally with Brettanomyces , whether they come from Bordeaux, California, South Africa, Merlot, Syrah or Tempranillo, they all end up having the same smell! Goodbye to geographical typology and varietal identity.
That said, it's all about style and taste. Some producers or amateurs appreciate or even seek this type of aroma. I do not care. But the famous “terroir taste” or the “typicality” of the vintage, the grape variety or the appellation should no longer be invoked to explain the smell of “leather” and “horse urine” that exhale. generously these wines: it is only the smell of Brettanomyces .
There are no really reliable statistics regarding the frequency of the “Brett” character in wines but only red wines, we will see why below, are significantly affected by this problem. The analysis of a fairly large number of bottles [5] showed that approximately 1/3 was potentially affected by a detectable defect during tasting (concentration of ethyl-phenols higher than the perception threshold in a red wine, i.e. approximately more than 600 µg/l for the 4-ethyl-phenol/4-ethyl-guaiacol 1:8 mixture most frequently observed in Europe). It would seem that the proportion is now higher year after year and that certain regions are more affected than others... This is why it seems necessary to me to take stock of the myths and realities surrounding this subject. in order to offer concrete solutions to those who really wish to master it.
Ecology and Origin of Brettanomyces in wines
This fundamental question has unfortunately been the subject of controversial treatment in recent years which has caused a lot of incomprehension and misunderstanding among practitioners... First of all, this micro-organism was presented as a "contamination yeast"; this term suggests that its presence is abnormal or exceptional in wines, which is completely misleading. In fact, this yeast is present in almost all fermentation environments, including wine. Then, various works have endeavored to demonstrate that Brettanomyces came from the grapes to suggest that it was the vineyard which represented the main source of “contamination”. Of course, Brettanomyces did not arrive from the planet Mars in a spaceship, or even on a meteorite… One day it had to enter a cellar via grapes…. However, and all microbial ecology studies have demonstrated this very well, the frequency of detection of this yeast on grapes is low or extremely low (between 0 to 3% of yeasts present) in the vast majority of cases. This is only in particular configurations, that is to say (i) a more or less damaged or over-ripe grape with a loss of integrity (porosity) of the skin [6], or (ii ) in the case of plots downwind of massive sources of contamination [7] (wine waste spread or piled up) that large populations can be reached and are likely to pose a problem in the cellars. These rare situations must be identified early, the harvest sulphitized at a higher level than normal (7-8 g/hl) then inoculated with an industrial leaven so as not to pose any winemaking problems.
But the rest of the time, it is the source of contamination by Brettanomyces ? Well, as for all the microorganisms at the origin of the transformation of grapes into wine: winemaking equipment in the broad sense! Brettanomyces remains little present, or even absent, from the microflora of fermentation processes because fermentation yeasts and lactic acid bacteria normally multiply more quickly and occupy their ecological niche more quickly. However, due to the characteristics of its metabolism (capacity to assimilate particular sources of nitrogen and sugars) and its capacity for adaptation (resistance to sulfur dioxide), at the first fermentation accident, it can quickly colonize the environment and cause then different alterations.
To explain the greater development sometimes noted in new barrels compared to used ones [8], the oak wood of the barrels has been suspected by certain “winemakers” of contaminating the wines early and promoting the multiplication of Brettanomyces. In fact, it's not the case! The explanation is quite different. First of all, Brettanomyces is not part of the normal wood microflora. Then, the new barrels are heated between 150 and 230°C which leads to their sterilization if they are contaminated... The quantity of sugars assimilable by Brettanomyces provided by new wood represents little compared to what exists naturally in wines [9]. Used barrels always represent a greater source of contamination than new ones because they potentially harbor a inoculum and may contain ethyl phenols in their mass [10]. However, in the presence of initially contaminated wine (that is to say in almost all cases as explained above), it should be noted that the kinetics of disappearance of free and active sulfur dioxide, the only antiseptic usable during breeding and active within a certain limit against Brettanomyces (see other chapter), is faster in new barrels than in used barrels (stronger oxidizing potential, higher evaporation). Thus, paradoxically, it follows that Brettanomyces can in certain cases develop more quickly in new barrels than in used ones, despite a inoculum much weaker initial. The level of sulfur dioxide and the topping must therefore always be checked more frequently in new barrels, particularly at the start of aging when the consumption is higher, to avoid this type of problem.
The question of cleaning and disinfection of wine containers, particularly those made of wood, is a critical point which will be specifically addressed a little later.
[1] CLAUSEN NH, 1905 Occurrence of Brettanomyces in American lager beer. American Brewers Review, 19, pp511-512
[2] KUFFERATH H., VAN LAER MH, 1921 Study of Lambic yeasts. Their chemical action on culture media. Bulletin of the Belgian Chemical Society, 30, pp270-276
[3] PEYNAUD E., DOMERCQ S., 1956 On the Brettanomyces isolated from grapes and wines. Arch Für Mikrobio, 24(8), pp266-280
[4 ] CHATONNET P., VIALA C., DUBOURDIEU D., 1997 Influence of polyphenolic components of red wine on the microbial synthesis of volatile phenols. Am J Enol Vitic, 48 (4), pp443-448
[5] CHATONNET P., DUBOURDIEU D., BOIDRON JN, PONS M., 1992a The origin of ethylphenol in wines. J Sci Foof Agric, 60, pp165-178
[6] BARBIN P. 2006 Control and control elements of contamination by Brettanomyces yeast during the red winemaking process. Thesis INSTITUT National Polytechnique de Toulouse
[7] CHATONNET P., MASNEUF I., GUBBIOTTI MC, DUBOURDIEU D., 1999 Prevention and detection of contamination by Brettanomyces during vinification and aging of wines. Rev Franç nol, 179, pp20-24
[9] CHATONNET P., DUBOURDIEU D., BOIDRON JN., 1995 The influence of Brettanomyces/Dekkera sp. yeasts and lactic acid bacteria on the ethylphenol content of red wines. Am. J Enol Vitic, 46, 463-468
[10] CHATONNET P., BOIDRON JN, DUBOURDIEU D., 1993 Influence of the aging and sulphiting conditions of red wines in barrels on the content of acetic acid and ethylphenols. J Int Vigne Vin, 17, pp 277-298
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