Troubleshooting Your Wine
The faults and flaws and their analysis and resolution presented below are from my latest book, Modern Home Winemaking, where you can find additional information should you wish to explore these further.
BRETTANOMYCES
DESCRIPTION
Brettanomyces, or “Brett,” as it is affectionately referred to, is a condition where wine (almost exclusively red wine) has an unappealing barnyard smell or medicinal, sweaty, “Band-Aid” and rancid aromas. Affected wine can also have some secondary symptoms including biofilm formation, cloudiness, color loss and volatile acidity (VA).
Winemakers partial to the barnyard smell may find that a little Brett adds complexity and may argue that it is part of their terroir, but others consider any amount of Brett an outright fault.
CAUSES
This fault is due to indigenous Brettanomyces yeast that metabolizes naturally occurring phenolic acids into volatile ethyl phenols, the compounds responsible for the offending odors and which have a detection threshold of about 600 µg/L (ppb).
Brettanomyces yeast can be very difficult to inhibit, even preventatively, in that it only needs very low levels of sugar, less than 275 mg/L (0.0275%), and very little nutrients to jump into action. Acetic acid is a by-product of Brett metabolism, and therefore, although VA seldom becomes detectable, there is an increase.
ASSESSMENT
This fault can be assessed qualitatively by smell; however, it can be very difficult to detect as the metabolic conversion by Brettanomyces yeast is very, very slow. The range of smells can vary greatly depending on strains and can be categorized more generally as animal, savory, woody, putrid, chemical/solvent, veggie, fruit, floral spice, fermentation, dairy and earthy. Detection of specific smells depends on the relative concentrations of Brettanomyces compounds in the wine matrix, not just their absolute detection thresholds.
Brettanomyces yeast has strong physiological resistance and can persist in the winemaking area and particularly in the barrel cellar for very long periods of time during which it can easily contaminate equipment and wine. Although some incorrectly equate this fault to poor hygiene in the cellar, it can aggravate the infection.
Brettanomyces can persist long periods of time in bottled wine too, having very good tolerance to typical wine alcohol levels and being only moderately sensitive to SO2.
REMEDIAL ACTIONS
Brettanomyces is very difficult to eradicate and can easily propagate to the entire winemaking area.
Chitosan has been shown to have some efficacy in treating infected wines. No Brett Inside is a chitosan product specifically formulated to treat Brett infections.
PREVENTIVE ACTIONS
Assume that Brettanomyces yeasts are always present, therefore be extra vigilant and practice good cellar hygiene. If you have had Brett infections in the past, consider using chitosan after completion of the MLF as a preventive measure. And don’t accept any wine (e.g., to supplement your production) from other producers known to have had Brettanomyces in their wines. Some wineries have strict rules of not accepting wine — any wine — from outside the estate for fear of contaminating their cellar.
Reds are at higher risk because of their greater phenolic content, higher pH, and that the wines are produced by macerating skins in juice. Ferment to complete dryness, i.e., SG below 0.995 (below –1.5 Brix).
Barrels pose a greater risk because they can harbor the yeast and because of their cellobiose content. Cellobiose is a sweet disaccharide produced from cellulose hydrolysis during manufacture of oak barrels. If you have access to an ozone generator and are knowledgeable in its use, an ozone treatment can reduce Brettanomyces yeast populations in barrels.
Choose a so-called “cinnamic esterase-negative” O. oeni lactic acid bacterial strain for barrel-aged or barrel-fermented red wines for conducting the MLF; do not rely on indigenous lactic acid bacteria. And minimize the time to complete the MLF and sulfite aggressively using a 100% FSO2 adjustment on the first KMS addition upon completion of the MLF. A minimum MSO2 of 0.5 mg/L is recommended for reds where Brettanomyces is a potential problem or as preventive.
Store and age wine at cool temperature, ideally at 13 °C (55 °F).
And sterile filter at 0.45 micron (absolute) directly into bottles, if possible.