jhc@hou5g.UUCP (Jonathan Clark) (02/12/85)
[] There are two points here. First, every brewer/vintner that I am aware of is fanatically careful about the strain of yeast used in fermentation. Second, a particular strain of yeast will produce a brew with unique chemical characteristics. It's not a case of purity control, but of the different yeasts producing different permutations of alcohols, aldehydes, esters, ketones and so on in the fermentation process. Part of the job of the brewmaster is to experiment with different quantities of the components of a beer and try each combination with a different yeast strain, to see what the results are (I have a friend who became a brewmaster at a real small brewery in London (Godstow's, I think - anyone know it?)). Different strains of yeast produce different amounts of different chemical goodies. It's the same as different beers/wines having different amounts of ethanol - it's not because individual breweries throw in different amounts of industrial alcohol, but because the yeast strain used for that brew dies off at that ethanol concentration. Some of these yeast strains have been around for centuries. When Lowenbrau licensed Miller to produce its lager in the US part of the deal (indeed, part of the process) was that Miller use Lowenbrau's strain of yeast (this strain started off in the thirteenth century sometime). As I recall, the trace chemical in booze that is the major cause of headaches is amyl alcohol. Napoleon brandy is supposed to be full (relatively speaking) of this stuff and thus should be avoided when drinking heavily. Vodka has none and thus is relatively pleasant to get drunk on. Jonathan Clark [NAC]!hou5g!jhc -- Jonathan Clark [NAC]!hou5g!jhc
rcd@opus.UUCP (Dick Dunn) (02/19/85)
> ...different chemical goodies. It's the same as different > beers/wines having different amounts of ethanol - it's not > because individual breweries throw in different amounts of > industrial alcohol, but because the yeast strain used for > that brew dies off at that ethanol concentration... Not true. Most beer yeasts are capable of producing as much as 10-12% alc (vol), which is about double what's typically present. Wine yeasts can probably tolerate 18-20% alc. Fermentation stops either because all of the fermentable sugars are gone--as with beers--or because the yeast is intentionally killed off chemically--as with some wines. The end product is then generally either filtered or settled out (perhaps with flocculating agents) to get rid of the remaining yeast, which can otherwise contribute off-flavors. Finally, almost all beers are pasteurized in order to ensure that no viable yeast (or other microbeast) remains to nibble on the brew. A few beers (from smaller breweries) are not filtered; the yeast is left in and the last little bit of fermentation takes place in the bottle in order to carbonate the beer. It's like Methode Champenoise except that the yeast stays in the bottle. The yeast sediment from the bottom of bottles of this sort can often be cultured into a usable yeast for brewing if you're VERY careful to avoid contamination. -- Dick Dunn {hao,ucbvax,allegra}!nbires!rcd (303)444-5710 x3086 ...Relax...don't worry...have a homebrew.
c-hunt@tesla.UUCP (Charles Hunt) (02/23/85)
Good point on yeasts. However, no wine yeasts can tolerate above 17% alcohol before they commit suicide. Fact is, most American wine-makers intentionally kill the natural yeasts in their musts before fermentation and then innoculate the vats with yeast, almost always a strain very similar to what is used by beer manufacturers. These yeasts can't survive over 14.5%. The only yeasts that can live above that level are some very hardy wild strains (one of which is used in Campagnia, Italy, and in high sugar years gets an intoxicating 16.8% before giving up the ghost). Most dry wines were fermented to below .5% residual sugar (below perceptable levels) and then racked to dispose of trace yeasts with the lees, or, in the case of the "modern" producer, centrifuged and filtered (which, arguably, gets other goodies as well). The sweet wines we enjoy (especially German) are cut short of finishing ferment- ation by cooling the must to inactivate the yeasties, at which point they are filtered or racked off, leaving the residual sugar. In some rare, and sometimes special, cases, the sugar is so high in the must that the yeasts die before leaving the wine dry (eg some BIG Amador Zinfandels at 14.5%) and the wine is "naturally" sweet. In some even rarer cases (usually with expensive rieslings) the must is innoculated with a gentle yeast which cannot take over 11% or so, and the bugs die leaving residual sugar, even though the must was not very high in sugar to start: but this trick is the work of only a clever and talented winemaker. Arguments as to the merits of one technique over the other are endless and futile, in my opinion. Cheers! Drink a little: live long. =Charles Hunt=