Wednesday, September 30, 2009

Behold the humble yeast








Behold the humble yeast: They turn sucrose (table sugar; C12H22O11) and water into CO2, heat, and alcohol (C2H5OH).





Without yeast, there would be no wine (though I suppose one could distill hard alcohol and add it to grape juice, but I don't see that product clogging the grocers' shelves).

Without yeast, no wine.
Without wine, chaos (surely).
Ergo, without yeast, chaos!



I've been studying yeast, preparatory to making some Viogner wine, and you know what? They are really just like goldfish. Like pet fish, they come in many forms, and have been bred (hybridized) for particular properties. Just within the ambit of enology, there are dozens of specialized yeast varieties that one can buy and use--some are for cooler ferments, some express fruits better, some are good for high residual sugars, some don't mind concurrent malo-lactic fermentation, etc. There is even K1-V1116, a "killer yeast" that engenders comparisons to piranhas; I'm using it on some Cayuga grapes right now (the yeast, not piranhas). And if you add in the myriad naturally-occurring yeasts that rest in their trillions upon the skins of grapes and elsewhere, the sheer number of types might boggle the mind.

Unlike pet fish, yeast can remain dormant in a dry environment, but they are most at home in water, such as the sweet and boundless sea contained in a single grape! They have a set of requirements, if they are to be able to function. Behold, the needs of wine yeasts:


1. They must be stored cool. Mine are by the butter dish in the fridge.

2. They need to be re-hydrated carefully. Not too hot and not too cold. Not for too long. Not with water containing chlorine. Not with must (grape juice) containing too much SO2 (sulfites).

3. The right quantity of yeast must be added to the must (the fruit juice). Too little, and it could take too long to spread throughout the must, allowing other organisms to reach the bounty first and make vinegar, acetone, or bitter wine out of your precious juice.

4. Like fish from the pet store, yeast must be introduced carefully to the must. If the must is too much hotter or colder than the yeast, it can shock the yeast into creating "petite mutants," reducing the rate of fermentation, or causing it to produce hydrogen sulfide (think rotten egg smell). And the must temperature must be at least a certain temp.

5. Like pet fish, yeast must be fed. In addition to sugar, they like nitrogen and phosphates. No french fries or pizza for your pet yeast, mind you.

Then, when the alcohol level is finally too high for them, they quit working, and go dormant. They sink by their millions into sludge at the bottom. They could be used again, but in practice (due to their contamination with undesirable stuff), they are sent to the septic tank or the sewage treatment plant. Almost makes you wonder if somebody will pick up the banner for them: "Prevent Yeast Abuse!" Give them pensions, or something.

And get this: Their mere existence in winemaking poisons their own environment, not unlike overpopulated humans in that way. They die as victims of their own success. Is the universe cold, or what?

But that is the life of wine yeasts. They sleep, dormant, forever if need be, but then are suddenly thrust into absolute Heaven, but only for a few days. For us, they make their Heaven into a Hell. One person's Hell is another's Heaven! Reflect on that, the next time you lift a wineglass.


Here's an article:
http://www.winegrowers.info/wine_making/Yeast.htm

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