by Andrew Chalk
I just spent a day in College Station in the most enjoyable way possible -- at a Texas A&M University course in “Wine Faults”. Almost everyone was either a winemaker or an academic taking a deep dive into the subject.
Wine Faults are important because, since wine is made (almost invariably) from grapes and the product of their fermentation and aging using universal techniques, all wines are subject to some degree or another to the same faults. Everyone in the industry can recite the names of the ‘Big Six’ but understanding their cause and amelioration is a totally different story. For example, it was brought home to me (as an outsider from the production process) how much ameliorating one fault is a compromise exacerbating another. The most headline-worthy finding was that you don’t need a cork to get cork taint!
The Big Six are: Oxidation, Brettanomyces, Hydrogen Sulfide (H2S), Cork Taint, Volatile Acidity, Malo-Lactic Fermentation in conjunction with high pH (low acid). In this series of articles I will report on each judged through the presentations by the faculty and graduate students who made them. Some of the findings are the results of primary research by the students themselves. The errors are all my own work.
BRETTANOMYCES
Brettanomyces, abbreviated to ‘brett’ in common parlance, is considered to be the most prevalent spoilage yeast in finished wine. However, there is a received doctrine that brett delivers a complexity that is pleasant. This is possibly why it persists vintage after vintage in certain wines.
EFFECTS
Professor Andreea Botezatu’s presentation delved into advanced chemistry but I shall describe the effects in layman’s terms. Brett causes
A loss of fruit, floral and honey aromas;
An increase in overall complexity;
An acetic acid, vinegar aroma;
A spice and smoke aroma;
A chemical, plastic, or ‘Band-Aid’ aroma;
A metallic, bitter taste;
‘Mousiness’
These are the result of a witches brew of chemicals with names like ethyl phenol, vinyl phenol, fatty acid, pyridine, aldehyde and more. The winemaker is most concerned with prevention and amelioration.
PREVENTION
Prevention begins in the vineyard. At harvest, pickers should place a rigorous focus on healthy grapes.
In the cellar, suitable hygiene practices should be followed. Pre-fermentation there are two important practices. First, sulfiting is the most effective preventive action. Second, a high temperature (>65oC) results in the inactivation (killing) of brett, and other microorganisms. Cold maceration (<10oC) deactivates but does not kill them.
During alcoholic fermentation brett’s ethanol resistance and lower nutrient demand means that it can grow as alcoholic fermentation slows down or stops. Prevention stresses inoculation of musts with selected yeasts, restarting stopped fermentation as soon as possible, use of nutrients only if strictly necessary to restart stuck fermentations.
Post-alcoholic fermentation conditions favor brett. Monitor the population and avoid high temperature macerations (40-45oC) or micro-oxygenation and the release of sugars in the case of uncrushed (whole berry) harvests. Start malolactic fermentation quickly before brett multiplies. When complete, add sulfur dioxide to eliminate microorganisms.
Interestingly, aging on-the-lees, one technique responsible for the deliciousness of big styles of chardonnay, is a risk factor. Clarification by any of the conventional means (racking, fining, and filtration) are important preventers of brett.
The barrel-aging stage is when wine is most vulnerable to brett spoilage. The wood that contributes so much positive flavor to wine also harbors brett. They are difficult to clean and no technique is 100% successful in removing brett from the internal stave surface or bunghole. Steam and ozone treatments seem to be the most successful. Once dry, sulfur dioxide should be used. Barrel shaving to expunge brett-harboring layers can also help. A new technique is ultrasound, which removes more than 90% of viable brett.
One lasting message that came through was that preventive actions are preferable to curative processes.
KEEPING UP TO DATE
Another faults workshop will take place mid spring 2023. For a definitive date and registration details keep an eye on their Facebook page (Texas Viticulture and Enology), where they post updates on upcoming educational programs.
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