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Re: Does Yeast reproduce in the flask


The answer is YES.  The doubling time for yeast under idea conditions is about 2hrs or less. You will notice that after you "refresh" the medium there will be a lag time with very poor CO2 production followed by vigourous C02 production. after a day or two things settle down and you will likely see a moderate but more constant CO2 production.  This is because the yeast grow very rapidly at first till they saturate the flask at a density that will remain constant under your conditions. As they do this they  rapidly convert the sugar to ethanol (anaerobic, hence the large CO2 burst) In the "wild" (PS the yeast you use are considered domesticated" ) this allows the yeast to kill off most of the other beasties the would also grow in the rich sugar medium. Once they have done this they settle down to a more leasurely growth and, if possible aearobically consume the ethanol.  Since yeast preferentially grow anaerobically one doesn't have to create an anaerobic enviroment for them to produce C02. 
I always restart my culture from ~10% of the old one. be careful not to use the sludge on the bottom  this will be less active yeast that will take longer to recover and grow again. 

In this fashion I have selectived for yeast that grow well in this application from a bunch of different lab strains. 

I have to go or I would type more =)

Tarah in dallas.