Winemaker's Question:I think that there is a lot more to Brett than just 4EP (or other types of spoilage for that matter). I can't imagine what else it's secreting into the wine that is effecting it's aromas, or overall quality.
Winemaker's Question:
I think that there is a lot
more to Brett than just 4EP (or other types of spoilage for that matter).
I can't imagine what else it's secreting into the wine that is effecting
it's aromas, or overall quality.
Sometimes it seems that Bretty wines are a bit rough in the mouth, and I don't know if that's due to the sensation of tasting 4EP molecules or some other chemicals produced from the Brett spoilage.
Z-Wine (SJL) Answers:
You refer to a well-known Brettanomyces biochemical pathway: the utilization of phenolics (by way of vinyl reductase and other enzymes) to make 4EP etc. Brett uses ethanol under anaerobic conditions - a very unique metabolism! So Brett has complex and relatively unique metabolic capabilities - many of which probably result in "spoilage" in one way or the other!
I Agree that Brett produces many more 'spoilage' metabolites in addition to 4EP & 4EG - I assume hundreds. In fact, some strains of Brett are known to produce little or no 4EP or 4EG, but instead introduce spoilage from other nasty off-flavors.
Winemakers know that Brett survives inside the wood of the barrels. Brett also uses cellobiose (from wood).
Cellobiose is an beta-1,6 dissacharide (2 glucose linked so they are unavailable to enzymes produced by animals) that is an acid hydrolysis product of cellulose. Wood is composed of cellulose, hemicellulose and lignin - I think about 1/2 cellulose. One might imagine the Brett biofilm adhered to the wood, releasing acid to bore into the oak and utilizing the cleaved cellobiose as it goes.
Pichia pastorisis and other spoilage organisms produce 4-EP & 4EG; many other sources (indoles, 6-CC, etc) of medicinal & chemical taints are associated with similar Brett-like defects (Australian Wine Research Instutute, 2006 Annual Report.)
For Brett levels in normal wine, the concentration of undesirable metabolites is very low. Metabolites defects become noticeable at Brett concentration greater than 105 cells/ml. Many good quality wines have low levels of 4ep/4eg. It is unnecessary (and potentially dangerous) to detect very low levels; it is undesirable to treat every barrel (Ref 3, SJL-confidential source.)
Winemaker's Question:
Compare the sensitivity of Z-Brett and
differential plating as Brettanomyces detection methods.
Z-Wine (SJL) Answers:
My suspicion is that if plating results:
Are negative, this DOES NOT assure that there is no Brett in the wine
Reveal a low number of colonies, this DOES NOT assure that Brett levels in the wine are low.
Brett lives as biofilm, adhered to the sides and in the wood. This makes sampling difficult.
Brett lives as VNC, plating often grossly underestimates the population (or results in FALSE NEGATIVES). In our field studies we found:
A differential plate result of several cells per ml, which when tested on
Z-Brett was positive with a 10^3 or 10^4 cfu/mL population
Our data supports the hypothesis:
"Typical plating of
field samples grossly underestimates the concentration of Brett in the
wine."