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.
VOLATILE ACIDITY
If your wine smells of nail varnish remover then it contains ethyl acetate. If it smells of vinegar then it contains acetic acid. Both things are faults, and together go under the category of volatile acidity (VA).
CAUSES
Acetic acid and ethyl acetate are the product of yeasts found on grapes. Different yeasts produce different amounts of both. Post fermentation, the two main bacteria that can cause elevated levels of VA are lactobacillus and acetobacter. All they need to reproduce is an aerobic environment.
In addition to the choice of yeast, certain winemaking practices favor VA.
Cold soaking, used to extract color;
Sluggish fermentation, maybe due to cold temperatures;
Barrel aging increases aerobic exposure;
Headspace in tanks and barrels;
Poor sanitation;
PREVENTION
Check grapes for quality the moment they arrive on the crushpad. Use inert gas to cover wine in tanks and keep barrels topped up. Treat barrels and tanks with sulfur dioxide. Sterile filter prior to bottling.
I recall some years ago receiving a shipment of wine from a startup winemaker who prided himself on not using filtration. After three years in my cellar half of the bottles were vinegar. Since he had not sterile-filtered, there were microorganisms and acetobacter in the wine that continued to reproduce over time.
REMEDIATION
The only way of actually removing acetic acid is reverse osmosis.
Experienced winemakers would say that prevention is the best medicine.
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.
The Wine Faults Workshop I attended was organized by the Enology team within the Department of Horticultural Sciences at Texas A&M. The group is led by Dr. Andreea Botezatu, and currently includes PhD candidate Cassie Marbach, PhD student Abby Keng and Master's Student Andrew Lyne. They are focusing their research on haloanisole taint remediation as well as verjus production and use as an acidifying agent, within the broader scope of sustainable practices in the winery and vineyard. For more up to date information about their educational programs (workshops, webinars, seminars) make sure to follow their facebook page: https://www.facebook.com/TXViticulture and subscribe to their YouTube channel: https://www.youtube.com/channel/UC5Oo5L0jMLR57IuUb0XmBxQ where they post recordings of Enology webinars and educational "how to" videos geared towards winemakers, winery lab technicians and enology students."
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