Wednesday, September 26 2007

It's Not the Yeast, At Least

Saccharomyces Cerevisae

Skipping back to the high-alcohol wine hobbyhorse for a minute, I've been hearing for the last few years that part of the problem can be laid at the vacuoles of the yeast used to ferment the sixteen-percent monsterwines. The theory goes that 'modern' yeast are so efficient at converting sugar to alcohol that they're getting more bang for the buck out of every must.

While I do own one of those cool white lab coats, I'm not a trained biochemist (sorry Mr. Harp, you did your best). But this has never rung true for me. First, there's no such thing as a 'modern' wine yeast used in the production of wine today, only recently identified strains that have most likely been around for a very long time.

Second, there's only so much sugar in any given fermentation. If the yeast are efficient at converting it, they'll run out of sugar and the wine will be dry. If they're poor at converting it, they will stop converting before it's used up, and there will be residual sugar left in the resulting wine. There's no way a yeast strain can make more alcohol out of the same amount of sugar--that's like getting more BTU's out of the same gallon of kerosene by using a different brand of matches to light your heater. Seems logical, but I didn't have any hard data to back up my gut feeling on the matter (when you've got this gut, you take it seriously.)

That is, I didn't have any data until I read Tim Patterson's Inquiring Winemaker column in the September issue of Wines and Vines. For those not familiar with Tim, like all men of that name he is handsome and smart, and is a prolific writer in the field of beverage alcohol (full disclosure: he writes for Winemaker alongside me, although he's a bit of a johnny-come-lately, showing up in 2002). He also blogs at Blind Muscat, and makes his own wine--what's not to love?

Tim's column puts his finger on the yeast/sugar/alcohol conundrum more concisely (and sciencely) than I have:

What yeast does during fermentation is take one sugar molecule and turn it into two ethanol molecules, two carbon dioxide molecules, some heat, and very small amounts of some other by-products. There's only so much carbon in the sugar to redistribute into the new substances--all the yeast nutrient in the world can't talk a yeast cell into making two and a half ethanol molecules, or three.

The column analyses a study by Lallemand comparing alcohol production with most of the wine yeast strains in use today, the upshot of which is

For the 56 of 60 white wine strains that were able to ferment to dryness, starting with 200 grams of sugar per liter, the resulting alcohol ranged from 11.75% to 12.09%, a spread of 0.34%. For the successful red strains, which started with a 280 grams per liter solution, the final alcohol ranged from 16.55% to 17.06%, a span of 0.51%.

Now I'm all tingly with vindication! But this leaves us with the truly important question of whom to blame for high-alcohol wines that are burning out palates and leaving poor, honest winebloggers haggard and staggering.

Wait, who said, 'global warming'?

posted by Tim at 05:34PM

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