February 22, 2006 - 9:42am
Yeast varieties
A question that came to me via email:
"Have you had any experience
with different types or varieties of yeast and how they affect the
flavor of the bread?
I do some homebrewing, and there are a mind boggling amount of yeast
available -- different yeasts for every different flavor and style of
beer.
Is there as much variety for bread yeasts? Is there a French strain
that makes better French bread? A certain yeast that works better with
rye breads? If there are different yeasts, can the average person
taste
the difference?"
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You can get some idea from wiki entry
http://en.wikipedia.org/wiki/Yeast
As for the flavor, I don't know since I don't use different region cultures. Maybe some people can answer that.
A long time ago, I did do some homebrewing and, yes, there is a dizzying number of yeasts, each with distinct flavor characteristics. In addition to the ethanol, carbon dioxide, and heat produced during fermentation, yeasts also produce trace amounts of aromatic by-products (some are esters, if I remember right). These complex collections of by-products give the distinct flavors of the yeast. In addition, the amount and types of esters formed also vary with temperature of the fermentation (which is partly why if you took the same yeast and fermented "warm" the beer had more estery, fruity flavors than a slower, colder fermentation).
The two main strains were ale yeasts (which if I remember correctly is the same strain that most commercial bread yeasts are) and lager yeasts, with the lager yeast tolerating colder temperatures (and partly explaining the smoother flavor of lagers). Most of us use commercially produced bakers yeast (and the differences in fresh, dry, and instant yeasts are probably more differences in the packaging of the yeast rather than distinctions in the actual yeast strains).
So, speculations on my part (I have NO facts, these are just guesses and they may certainly be wrong). First, the yeast in bread do not ferment to completion as in beer, so perhaps not as much of the aromatic by-products have been made. Second, the unfermented beer (called wort) is sanitized and then fermented with the pure addition of the yeast culture. Wild yeasts and the odd bacteria are not welcomed in beer making (with a few odd exceptions, such as Belgian lambics and some indigeous brews). The nice, complex tang of sourdough is strongly due to the bacterial component. Third, I wonder if the baking process drives off some of the volatile aromatics that may have been produced by the yeasts.
Certainly, the sourdoughs (and levain/biga) have great regionally distinctive tastes, but again it may be difficult to separate the contributions from wild yeasts versus the regional bacteria.
Just some speculation on my part. Interesting question, though.
Mr. Peabody
The differences in taste for sourdough breads are actually a combination of the wild yeast and bacteria. Certain bacteria only coexist with certain strains of wild yeast, and as such, having different yeast invites different bacteria. From my understanding, both yeast and bacteria contribute to flavor, although I think it's the bacteria that creates the "sour" in sourdough.
As for commercial bakers yeast, I think that I read somewhere that pretty much all commercial bakers yeast falls into a single strain, so there shouldn't be too much difference in taste from one to another - the differences in taste are instead related to the time/temperature of fermentation (which is also a huge role in the strength of the sour in sourdough).
I can't speak regarding yeast for the brewing process, because I am not at all familiar with it...
I'm by no means an expert, but I'm pretty sure that this is accurate :)
The only varieties I am familiar with are fresh, dry active, instant and wild yeasts. I think the fresh is a little more pungent than the active and instant yeasts and certainly the wild yeasts (sourdoughs) vary in flavor. There is some information on http://www.foodsubs.com/LeavenYeast.html
Nancy