Brettanomyces
Study of red wine contamination by Brettanomyces yeast
Gilis J-F., Cabri C. et Ducournau P.
A joint study carried out by the Oenodev Research & Development Team, along with Professor Stréhiano's Fermentation and Bioreactor Team at the ENSIACET* at Toulouse.
Presentation
Brettanomyces yeasts were discovered in 1904 by Claussen who noted their presence in beer musts (Larue et al., 1991; Licker et al. 1999). This yeast is not of any particular industrial interest; any studies carried out on them were essentially meant to discover means of avoiding them. They are mainly to be found in fermented drinks like beer, wine or cider.
The problems caused by this yeast in the oenological sector are of an organoleptic nature. It has been proved that it is capable of developing in wines during maturation (Froudière & Larue, 1988) or when bottled, and can produce, through degradation of phenolic acid, malodorous compounds, such as 4-vinylphenol and 4-vinylgaïacol (Heresztyn, 1986) (a+b); Chatonnet et al. 1995; Baumes 1998; Gunata, 1998). The odours caused by the development of this yeast are varied : animal (musk, venison etc), stable, horse sweat, leather, pharmaceutical, ink, gouache, plastic, burnt rubber.
Brettanomyces yeast seems capable of producing at least 10 different aromatic components which destroy the fruity characteristics of the wine (Licker et al., 1999). Various types of wine may be contaminated - white, red, sparkling.
Although, in rare cases of fermentation musts, this yeast has been isolated (Wright & Parle, 1973), it appears to be typical of wines left to age in barrels (Larue et al. 1991; Fugelsang, 1998)
No case of contamination mentions the presence of a majority of Brettanomyces in the musts during fermentation, while Froudière & Larue (1988) note that Brettanomyces can develop together with Saccharomyces during fermentation.
We are not yet sure which ecological niche Brettanomyces fits into. Any studies carried out on this have shown it's presence in rare cases on bunches of grapes (Arojo et al. 1998; Pretorious 2000), and in wine storehouses (Peynaud & Domercq, 1956).
They have been more often found on the organic deposits in pumps used to transfer the musts and as such, seem to be linked to hygiene conditions (Fugelsang, 1998). In certain cases, Brettanomyces produced a veil on the surface of contaminated wines, linked to an abundant production of acidity (Galzy & Rioux, 1955). Brettanomyces is thus considered an alteration yeast which could contaminate musts and wines during pre and post fermentation operations ; however, its exact origin remains a mystery.
Since 1995, the method of micro oxygenation used to optimise wine maturation, has proved itself. But it is sometimes suspected of favourising the apparition of contamination microorganisms, particularly Brettanomyces (Lonvaud-Funel, 2000). Oxygen does indeed stimulate growth and alcoholic fermentation in Brettanomyces, it also stimulates acetic acid synthetis (Aguillar Uscanga 1998). On the other hand, in anaerobiosis, the concentration of acetic acid produced is very low (Ciani & Ferraro, 1997; Aguilar Uscanga 1998) or inexistant (Blondin et al., 1982; Larue et al., 1991; Gilis et al., 1999), depending on the author.
The relationship between Brettanomyces and oxygen is rather complex. In 1940, Custer showed that oxygen stimulated fermentation of Brettanomyces claussenii. This was inconsistent with Pasteur's findings concerning Saccharomyces cerevisiae ; this phenomenon was called « negative Pasteur effect ». Scheffers later showed that the Pasteur effect and the negative Pasteur effect are conditioned by different mechanisms and can, with many yeasts, occur simultaneously during alcoholic fermentation.
So as to avoid any confusion, Scheffers introduced the idea of the Custer effect - blockage of alcoholic fermentation during passage to anaerobiosis (Scheffers & Wiken, 1969). These same authors showed that this effect occurred with all Brettanomyces yeasts and suggested that this phenomenon was a taxonomic criteria of the type.
Passage from aerobiosis to anaerobiosis suddenly interrupts fermentation and Brettanomyces growth. However, this fermentation blockage is temporary, and after a latency period, fermentation starts again, much more slowly than with aerobiosis. This impediment can be eliminated through oxygen supply, or through adding hydrogen acceptor compounds, like carbonyl compounds.
Among these compounds, Wikén (1967) mentions acetaldehyde, acetone, acetoine, and pyruvic acid; there are, however, other compounds, able to play the same role as carbonyl compounds. Gilis (1999) adds that, in the absence of oxygen, nitrates make it possible to accelerate Brettanomyces fermentation, more efficiently than acetoïne.
He concludes that all compounds likely to be "reduced" by Brettanomyces are capable of also capable of favourising its fermentation in anaerobiosis.
However, Brettanomyces growth conditions during wine elevage are very different from fermentation conditions. The role of oxygen in post-fermentation Brettanomyces growth remains to be defined. The purpose of this study is to determine the effects micro-oxygenation has on Brettanomyces development in post malolactic fermentation conditions and to specify the effect this yeast has on the quality of the final product.
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