Help : ethanol productivity of yeast and pH control in fermentation - (Oct/19/2011 )

we wanted to test the ethanol production of yeast in fermentation by GC techniques. during the fermentation, pH level was controlled and set up at pH7. so what i think is no matter how much the yeast produce the ethanol in fermentation broth, the broth's pH is monitored to 7 by adding NaOH solution. so there would not be ethanol in it.
so if we want to test the ethanol productivity of yeast , we should not monitor pH and let pH change by its course so that we can use GC method and find out the concentration of ethanol produced.
but my colleague said the ethanol can be still detected as it is formed as CH3Ch2ONa in the broth by using the GC. so we can still control pH at 7 and detect the ethanol productivity of yeast in fermentation.

which one is correct ?

if you know, please share your thought. it really confuses me.

thanks

This isnt my field exactly, and this is just off the top of my head, but do yeast not need a slightly acidic environment to produce EtOH? Why would the pH matter when you're analysing EtOH content using GC? Again, maybe someone else can be abit more specific and helpful!!!!

Hola, in my far in the time experience, aerobic formation of ethanol is independient of pH but depends of sugar (glucose) concentration.When sugar levels arise of about 1g/l the ethanol production is certain (crabtree efect), because I think that you want increase biomass withouth inhibition of grow by ethanol. So you have to feed fermenter with a feed-batch method mantaining sugar concentration less that the umbral glucose.I used a diabetic strip glucometer for fast detection of sugar levels and a colorimetric sigma ethanol test. About your colleague opinion sodium acetat comes from acetic acid a total oxidation product that Im not sure that it will be produced in yeast , it is produced in E. coli when sugar levels increase of this umbral value of 1g/l . Buena suerte

Hi FlicFlak , Protolder

Thank you very much for your answers. your points make sense !

Best regards
M