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.
It is hard to think of a more enjoyable thing to do after breakfast than attend a presentation on oxidation in winemaking. Andrew Lyne, a Ph.D. candidate, did the honors.
WHAT IS IT?
The effects of oxidation are a loss of fruit quality and browning. Aromatic white wines are more affected than tannic, phenolic red wines. The slides from Andrew Lyne’s presentation were replete with chemical formulae with intimidating subscripted numerals. Here, I give my “Oxidation for Dummies” version.
In everyday terms, oxidation is the process of wine’s interaction with oxygen. Perhaps surprisingly, this can occur at five stages: in the vineyard, during pressing, post fermentation, per/post bottling, and aging.
HOW IT HAPPENS
In the vineyard and during pressing, oxidation occurs due to one or more of poor canopy management for disease, poor fruit quality, the transport time to the winery, and the time in between processing and fruit delivery to the winery.
Post fermentation, oxidation occurs due to excessive oxygen exposure (common examples are barrels not being topped up and bunged, ullaged tanks, and tank lids left open), inadequate gas usage (carbon dioxide, nitrogen, or argon), insufficient free sulfur dioxide, or faulty corks or screw caps.
There is, of course, a ‘base level’ of oxygenation inherent in winery operations. Figure 1 (reproduced from Andrew Lyne’s presentation) shows the levels of oxygen ingested due to common winery procedures. I found it striking how much ingestion can be reduced with the use of inert gasses (98% or better) and how splashing can frustrate all other efforts to reduce oxygen pickup.
Prevention of oxygenation falls to eight key techniques:
1. Reduce botrytis through good canopy management;
2. Inert gas blanketing (carbon dioxide CO2 and/or nitrogen N2);
3. Sulfite additions (Sulphur Dioxide SO2 is extremely effective in preserving wine). At bottling, specific limits for dissolved oxygen, free SO2, dissolved SO2, and pH ;
4. Keeping Barrels Topped Up;
5. Minimize Headspace in Vessels;
6. Age Wine in Cool Storage Vessels;
7. Choose Correct Bottle Closure;
8. Check Dissolved Oxygen Levels During Winemaking;
DIFFERENT TYPES OF WINE CLOSURE
Different closures have different degrees of oxygen permeability…
There are remediation methods but prevention is the best approach.
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.