Common sense winemaking

Wines & Vines, Nov, 1996 by Richard G. Peterson

Your goal sounds good on paper but just isn't workable in practice. One winemaker's natural yeast is likely to be everybody else's spoilage yeast. Wild yeasts are treacherous unless you live in one of the isolated few parts of the world in which no fruit except winegrapes are grown. For success, the wild yeast where you live needs to be wine yeast.

You won't learn anything worthwhile even if you get a professor or his student to come out and sample the bloom on every single grape in your vineyard for plating. The reason is that the yeast population mixture identified on the skins of your grapes in the field isn't going to be the yeast that ferments your grapes into wine.

Over and over again this has been checked and the answer is always the same: regardless of whatever yeast starts your fermentation, the population at the end of that fermentation is dominated by Saccharomyces cerevisea. Not pure, 100% cerevisea mind you, but a fermentation that ends up being dominated by that yeast regardless of what started it.

We know that nature constantly evolves towards variation and complexity over time. And that's just as true for wine yeast as for anything else. It is probably impossible to find a commercial fermentation that was carried out by any single yeast strain. Sort of like expecting to find a large country anywhere in the world with a population composed only of blondes - or only right-handed people. Somebody's law, I think.

The fact is, Saccharomyces cerevisea has a one-track mind and fermentation of grape juice is what it knows to do better than all others. But it doesn't easily hang around on new leaves and fruit each year in great numbers. After all, none of the leaves and fruit on a vine this year were there last year. Neither will the same leaves and fruit clusters be there this year. Whatever appears on the leaves and fruit in a given harvest season must have blown in on the wind during the summer and/or early fall of that same year.

Disposal of stems, pomace and lees in the vineyard each fall certainly provides a stockpile of S. cerevisea into the soil. Some of these cells will survive until next season, when wind can blow them up onto the growing vines. Eventually some may stick onto the skins of new fruit, becoming part of the dusty "bloom." But they always have to compete with large numbers of wild yeast which are meaner, tougher and better able to survive the elements. It seems illogical to expect that the wild yeasts which are tough enough to survive the elements are also strains which have enough finesse to produce the finest wines. Sure, it could happen, but that kind of coincidence isn't common in nature.

My personal belief is that California winemakers are asking for problems when they don't use a pure, cultured wine yeast for fermentations in the first place. California grows lots of fruits other than wine grapes and many tons of these fruits ripen, get overripe and then rot on the ground, where they spew countless hordes of Mickey Mouse yeast strains into the air. Those that survive the winter lie in wait for unsuspecting winemakers next year. Because wine yeast, they ain't. Ask yourself these questions.

* Should you trust your winemaking reputation to "whatever wild yeast happens to survive the elements and stick to grape clusters in the field"?;

* Isn't it wiser to use a time-tested, cultured wine yeast which has already proven itself to be reliable?;

* Suppose you happen to get an acceptable and clean fermentation from wild yeast this year. Is it really smart to bet your future that nature will repeat this performance next year, and then again the next?

With some varietal grapes commanding prices of $2,000 per ton in 1996, that's a pretty big risk to take unless you know absolutely that the yeast you use will perform perfectly.

To be fair, the above point of view is not universally accepted. Some think of it as boring, overly cautious and incapable of producing that "great leap forward" that all winemakers seek. Those who rely on wild yeast often report that they have, indeed gotten the great results they wanted from wild yeast (today's savvy P.R. term is "natural yeast" - never mind that all yeasts are 100% natural).

Should we believe the claims of increased complexity with wild yeast? Well, maybe, sure, sometimes. It's entirely possible that flavor complexity might arise from wild yeast and bacteria growing for a while in the juice before the S. cerevisea takes over and completes the fermentation. But jungles produce far more bad odors than good ones. Common sense says it's more likely that wild growth will produce off flavors than good ones.

Brettanomyces (Brett) is a ubiquitous wild yeast which has probably ruined more wine than any single yeast. It occurs everywhere in nature, certainly in all wineries, and it can destroy wine permanently in a short time. Badly-infected wines contain prominent barnyard-like odors and Brett off-flavors which never improve with age. Yah, I know, at least one wine writer actually likes it - but does that mean winemakers should accept spoilage in their wines just to please the wrong palate?