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My experience with the yeast-sugar CO2 production method is not very good.
When I first set up such a system, it worked reasonably well, but
subsequent batches had been problematic. The bottles of yeast-sugar would
bubble like crazy very quickly and then die out in less than 24 hours.
Adding baking soda and starch helped a little in that some bubbles would be
produced after 24 hours, but the rate is so small as to be useless. Since
yeast (according to my microbiology book) do not produce enzymes capable of
breaking down starch, I figure that any CO2 production must be the direct
or indirect result of contaminants ie. other unknown microorganisms in the
bottle; not a very useful piece of information.
I have tried a modification that seems to work much better. First I
sprouted a handful of mung beans by soaking them in a bit of water for 12
to 18 hours (It is very hot here in Singapore, so others may have to let it
sprout a bit longer.) The sprouts were then crushed (finely) in a pestle
and mortar to kill the beans and also to release the amylase. To this I
added 2 tablespoon of corn starch powder and 1 teaspoon of bakers yeast
which I had been using. I then put everything in a 1.5l soft drink bottle
and top up to half full with water. Theoretically, in a set up like this
the rate of CO2 production is determined by the amount of amylase one
started out with since yeast can only use sugar, derived from the breakdown
of starch by the amylase, for respiration. The amylase are produced by the
sprouting beans and once they are killed, that should be a constant.
Of course any starchy seed and starch powder should work; mung beans and
corn starch powder just happened to be conveniently available for me.
Anybody wants to try some corn flavoured-mung bean beer?
Richard KHOO Guan Chen
email:- khoogc at singnet_com.sg
snail mail:- 38-A, Lorong 23, Geylang, Singapore 388372