The yeasts of commerce are baker's yeast and brewer's yeast which are
different species although closely related. Both belong to the same genus
of single cell ascomycetous fungi called Saccharomyces. Baker's yeast is
Saccharomyces ellipsoides and brewer's yeast is Saccharomyces cerevisiae.
Both ferment sugars the same way (to carbon dioxide and ethanol) but minor
products of their action powerfully influence flavor. You can ferment
grapes or flour with either yeast but the flavor of each product will
reflect on the type of yeast used. The wild yeasts used in sourdough are
often only distantly related to the two commercial yeasts and, although
they ferment sugars by the same biochemical pathway, they also produce some
organic acids that impart the special flavors we like.
You can use either yeast to make soda, such as root beer, but if you use
baker's yeast the soda will taste yeasty in the way bread does. Also the
yeast will not settle out on the bottom of the bottle in a sufficiently
hard lump as will brewers yeast and when the bottle is slightly agitated
during opening the yeast will be stirred up. Serious home soda makers
ultimately use a champagne strain of S. cerevisiae selected to form a hard
deposit in the bottom of the bottle. Alcohol is produced by any yeast in
making soda but the amount is very small. Only sufficient sugar is added
to create 1-3 atmospheres of pressure (ie., fizz) in the soda bottle.
When the sugar is used up only a tiny amount of alcohol is present. You
can blow up even chanpagne bottles if you add too much sugar. To retain a
sweet taste in the soda add non-sugar sweetners.
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From: Tom A Brown <EUSTOBR@am1.ericsson.se>
Subject: Yeast behavior
Date: Mon, 6 Apr 1998 11:02:46 -0500
Bread yeast & brewer's yeast are different, apparently not
interchangible.{due to flavor?]
I am interested in the differences in how yeast(s) behave. How can
such a simple mold be so smart??
I realise it takes a tangent away from just bread, so sorry in
advance, and skip it if your not interested.
I have a excellent [meaning I don't know the answer!] conundrum
on which some
of the brilliant & diverse minds that read these postings
perhaps could shed some light.
Home brew beer and soda both use (the same) brewer's yeast.{
Why not bakers yeast?
And why not bake bread with Brewers yeast?}
I "know" that yeast acts on the sugar to produce carbon
dioxide (the "fizz" in technical terms) and alcohol. I also
thought I knew that
the yeast continued doing this until the "food" (sugar/starch) ran
out or the
alcohol concentration got to high, with the latter being the norm
for
alcoholic beverages. But such is (obviously) not the case with
soda.
Why is there no alcohol produced in the homebrew soda process, and
what stops the yeast? The two batches I've tried have varied from
slight fizz to moderate fizz -(variation between bottles) -never
alot
of fizz. Yet I know there is still a lot of sugar in there! (And no
alcohol!??) What part of Chemistry 101 did I miss?
Tom Brown