Napa Valley Wine Radio

Question from Caryll: My father, husband and I have been discussing what is maximum possible alcoholic content in non-fortified wine. Not sherry, port madeira etc. I have noticed the creeping increase in alcoholic content and have preferred the French wines, which until recently hovered around 12%. I seem to recall wines which reached almost 17% but my husband says he thinks that it is impossible to make a wine of more than 14.9%. Help please! And if you could explain why as well…

Reply: Hi, Caryll! Thanks for writing! I swiped this quote from The Winemaking Page: “Nothing about wine is more lasting - or astonishing - than fermentation.” Matt Kramer, Making Sense of Wine.

It’s true that most wild yeasts have a very low alcohol tolerance, often dying off at 5% or less. They say that if you collect grape samples from vines anywhere in the world and analyze the juice, you’d find numerous strains of yeast, some helpful, others not. That’s why we know wine was discovered by mistake.

It wasn’t until the 1800’s that we realized that yeast is responsible for fermentation and, since then, we’ve gotten better at isolating the helpful yeasts. These days most of the world’s wine and beer is fermented with a yeast species called saccharomyces cerevisiae. Quoting Jancis Robinson, it “evolved from ancestral yeast by a process of genome duplication, rearrangements and deletions, estimated to have occurred over the past 100 million years.”  Within the species there are several hundred strains with differing characteristics. One of the species’ distinguishing characteristics is very good alcohol tolerance and, as you pointed out, that becomes important when the alcohols start to creep up as they have in recent years.

You can see on this page that, depending upon which yeast the winemaker purchases, there is more or less alcohol tolerance depending upon which yeast strain is selected. Some of these yeasts tolerate upwards of 15% alcohol as a matter of routine.

Winemakers select yeast first for practical considerations, such as lack of off-flavor, heat or cold tolerance, performing well in a barrel vs. a tank, settling nicely when the fermentation is over and, of course, alcohol tolerance. But the science has advanced to the point that certain yeasts are chosen for contributing to flavor or accentuating certain varietal characteristics.

“Wild” or “native” fermentation, in which no yeast is added, is usually a mix of yeasts that inevitably include saccharomyces cerevisiae if wine has been made on the site before. It works its way into the vineyard and becomes part of the winery and is, most likely, the yeast that ultimately gets the job done.

Your husband’s idea that the wine can’t be higher than 14.9% may have something to do with wine tax laws. We’re certainly allowed to produce high-alcohol wines, but when we go over 14% we are taxed as if we made a fortified wine, to which the alcohol is added, and our $1.07 per gallon federal tax goes up to $1.57.

I hope that helps settle your family debate. For everything and more that you might want to learn about yeast, grab a glass of wine and try going to this page.

Cheers! Nancy