How did Brett get into my wine?

Many winemakers and tasters will exclaim using a vulgar descriptor to express their distaste for wines infected with barnyard smell.

Regardless of personal tastes and preferences, if a farmyard aroma is subtle, it is considered acceptable and is often desired by many winemakers who claim that it adds complexity to certain styles of wines. But when the aromas are dominated by a strong barnyard smell, then it is considered a fault. And such is the nature of the indigenous Brettanomyces yeast, more affectionately known as Brett; it can have a positive influence on the wine, for the connoisseurs who like it, or it can spoil it completely.

Brettanomyces brusselensis yeast is the anamorph (non-sporulating form) of Dekkera bruxellensis yeast, which causes like-it-or-not barnyard odors, or medicinal, sweaty, band-aid, and rancid odors; these are the results of three main compounds, 4-ethylphenol and 4-ethylguaiacol, often referred to as 4EP/4EG, and 3-methylbutyric acid, also known as isovaleric acid, which can be detected at very low concentrations.

4EP, the most important compound as it is responsible for barnyard odour, is the product of decarboxylation (COO is removed) of p-coumaric acid and reduction of its intermediate. The main source of p-coumaric acid in Brett-affected wines is toasted oak wood, as the yeasts begin to feed on cellobiose, a sweet disaccharide produced from the hydrolysis of cellulose during the oak toasting process. . The reaction is very slow and can take several months or more, making detection difficult. Sulfite is not an effective treatment against Dekkera/Brettanomyces in barrels as the yeasts can hide deep in the cracks and crevices of the wood where sulfur dioxide (SO2) cannot reach. Therefore, it is strongly recommended that barrel-aged wines be sterilized prior to bottling to remove yeast, particularly when positive identification cannot be achieved.

Commercial wineries use dimethyl dicarbonate (DMDC) to treat contaminated barrels; however, this is beyond the domain of home winemaking and small wineries, as specialized equipment is required that can only be handled by trained personnel.

Brettanomyces/Dekkera they are glycophilic yeasts, which means that they also feed on glucose, that is, very small amounts of glucose, and convert it into acetic acid, also putting dry wines at risk. At high glucose concentrations, as in sweet wine, the volatile acidity (VA) can increase significantly and cause acetic deterioration, detected as the familiar odor of vinegar.

the challenge with Brettanomyces yeast is that it thrives easily throughout the cellar and is difficult to eradicate, particularly as it seems to adapt to changing environments. It is an anaerobic microorganism, which means that it thrives in the absence of oxygen. Specifically, it thrives in cellulose-fed oak barrels, or in wines with residual sugar, high pH, ​​or high concentration of polyphenols. Red wines are inherently more susceptible to Brett due to their higher pH and high concentration of polyphenols. Residual sugar is not usually a problem in whites because (if) they are well protected with sulfite; in reds, however, where the style must be a dry wine, the residual sugar can be a food source for Brett.

eradicating Brettanomyces it is almost impossible except by sterile filtration. But Brett is sensitive to free SO2 (from sulfite), so it’s easily preventable. Here are some tips on the best way to avoid a Brett infection in the cellar and wines from it.

o Ferment red wines until dry as much as possible for dry style red wines.

o Maintain a low pH in the recommended range for your style of wine.

o Use SO2 judiciously, taking into account the pH of the wine, paying special attention to wines rich in phenols.

o Do not age wine on lees for too long, as they are a source of nutrients for Brett.

o Store wine in a cool cellar, ideally at 55°F (13°C).

o Keep bottles, tanks, barrels and all other containers well filled.

o Filter sterile wines before bottling.