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  • andychalk


Updated: Feb 6, 2023

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.


Malolactic fermentation (MLF) is a normal and widespread process that usually follows alcoholic fermentation, and it is responsible for such things as buttery, creamy chardonnay and viognier white wines. It also reduces the acidity of a wine. However, MLF can have negative effects in the presence of high pH’s and lead to the formation of many fault-related compounds. At the least, in low acid wines, the softness of lactic acid (vs. the precursor, malic acid) can lead to flatness. It can however, more often than perhaps realized, end up in spoilage.

Metabolism of lactic acid bacteria (LAB) such as Pediococcus and Lactobacillus under high pH conditions (ph >3.6), can drastically differ from their normal behavior at pH < 3.6, resulting in the formation of numerous undesirable metabolites that end up spoiling the wines, as described below.


Ropiness - presenting as viscous threads, thick consistency and oiliness, usually in white wines;

Volatile phenol production, usually in high pH red wines. Look for odors of horse sweat, horse stable, leather, asphalt, mold, medicine and smoke;

Biogenic amine development. In high pH wines. Certain amino acids are converted to histamine, and tyramine and can cause human health concerns. (headaches, allergic reactions) Also, less harmful, but no less pleasant, putrid, meaty, vinegary dirty aromas are possible.

Metabolism of non-fermentable sugars in dry wines after alcoholic fermentation completed. This can produce acetic acid;

Mousiness from high pH, oxidative conditions;

Masking of varietal aromas that decrease fruit character and may produce nutty, yeasty, lactic and wet fur aromas;

Glycerin decomposition resulting in bitterness;

Tartaric acid decomposition in high pH, low total acidity wines, leading to a total acidity decrease, increased volatile acidity, color loss, and cloudiness;

Presence of unfermented sugars in wines with stuck alcoholic fermentation allows them to be accessible for LAB metabolism. This leads to an increase in total acidity, volatile acidity, loss of complexity and balance, and cloudiness;


pH level. At pH 3.6 and above, LAB are more likely to decompose sugars, tartaric acid and citric acid!

Fermentation of sugar leads to higher volatile acidity (VA) levels in wine.


Controlling wine pH is one of the keys to controlling wine spoilage by LAB;

Sulfur dioxide. A highly effective tool that is assisted by low pH;

Alcohol. Some LAB are killed off by higher alcohol levels, but not all.

Oxygen is favorable to the growth of LAB;

Carbon dioxide is favorable to the growth of LAB;

Nutrients. LAB needs a source of energy such as carbohydrates or inorganic salts. They also need vitamins and amino acids. Prolonged yeast contact can render a wine vulnerable to attack by LAB;

Vinification practices to prevent the growth of LAB

Fruit condition: Low population of LAB on the surface;

Must treatment: Use sulfur dioxide or risk bacterial spoilage;

Acidification: High pH musts with low acid levels should be adjusted with tartaric acid or other acidification methods.

Must clarification: Clarifying white must by settling or other means reduces suspended solids and nutrients. This discourages MLF;

Fermentation conditions: Stuck fermentations allow LAB to attack sugar and increase VA levels in wine. Rapid, even, fermentations to dryness are good practice;

Skin contact time (in the case of red wine), longer lees contact increases likelihood of a LAB attack;

Wine clarification: Early racking recommended. Use fine filters;

Winery sanitation: Clean and sanitize all equipment and containers;

High pH winemakers should also seriously consider inhibiting MLF altogether. Several products are commercially available and have been proven effective as LAB suppressants (Lysozyme, Fumaric acid, Nisine, Bactiless)


Preventing the harmful effects of LAB is a continuing task of measuring and correcting. Without a solid grasp of these techniques it is doubtful the winemaker would produce anything remotely drinkable.


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: and subscribe to their YouTube channel: 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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