Yeast growth on ethanol

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Kaiser

Kaiser

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This was new to me. According to this description: Lab #2: Yeast Fermentation yeast can utilize ethanol as a carbon souce if oxygen is available:

3) The oxidation of ethanol, which predominates when fermentative substrates are not available or in very limited supply. The cells attain a maximum specific growth rate of about 0.2 hr-1 with a high biomass yield of about 0.6-0.7 g dry mass per gram ethanol consumed, a low respiratory quotient of about 0.7, and an energy yield of about 6-11 ATP per mole of ethanol metabolized. The stoichiometry of this reaction is:

C2H5OH + 3O2 --------------> 2CO2 + 3H2O +
Click to expand...

does this mean that when we continue to aerate starters that have fermented out and provide more nitrogen to the yeast that we will get more yeast growth? Interesting concept. The absence of sugars will however cause flocculant yeast strains to flocculate but that should not be a problem with sufficient agitation.

Kai
 
It is new to me too. From the genetic perspective of the yeast better to keep making more yeast cells for when food is next abundant I guess.

Hmm.
 
Sure makes sense. Just like humans catabolize ethanol in the presence of oxygen. The yeast produced would probably be less than ideal to start a beer ferment as they will be terribly hung over ;)
 
It looks like as if this ability of the yeast is largely unknown to brewers. And for a reason: there is little or no practical value for brewing. Since oxygen is involved it cannot even be used for making low alcohol beer. I do wonder how good yeast gown on ethanol for the 2nd half of a starter would be in a beer.

Just for the geek factor of it I’m interested if one could demonstrate this effect in a starter. The idea would be to continually aerate the starter and record its gravity. There should be a decline as all the sugars are consumed followed by a slight rise as the alcohol is consumed. Nutrients may need to be added to keep the yeast going and a low flocculating strain may be better than a highly flocculent one.

Kai
 
I guess doing this for a starter would be alright, but are there any potential consequences of having oxygen involved post-fermentation?
 
Kaiser said:
It looks like as if this ability of the yeast is largely unknown to brewers. And for a reason: there is little or no practical value for brewing. Since oxygen is involved it cannot even be used for making low alcohol beer. I do wonder how good yeast gown on ethanol for the 2nd half of a starter would be in a beer.

Just for the geek factor of it I’m interested if one could demonstrate this effect in a starter. The idea would be to continually aerate the starter and record its gravity. There should be a decline as all the sugars are consumed followed by a slight rise as the alcohol is consumed. Nutrients may need to be added to keep the yeast going and a low flocculating strain may be better than a highly flocculent one.

Kai
Click to expand...

What you want to show is a continued growth of biomass even when fermentable sugars are down to zero. This could be done with a shaker table setup with 30 minute samples measuring optical density for instace - to plot out a growth curve. You will need parallel samples showing reducing sugars etc.
 
A way to limit DME (if you use it ) use in starters? Would making two starters, one with a second DME addition, and the other with only a second nutrient addition allow for a decent comparison of yeast slurry?

If the yeast did make good use of the ethanol, could a drop off in ABV be recordable? Would the yeast be poorly conditioned for pitching?

I need to get a frickin stir bar and flasks to make use of my plate.

menschmaschine said:
I guess doing this for a starter would be alright, but are there any potential consequences of having oxygen involved post-fermentation?
Click to expand...

Could always decant (you were talking about post fermentation a starter right?)
 
JKoravos said:
Sounds like you're volunteering. ;)
Click to expand...

I think eventually I'll do that. But right now there seem to be other more practical topics that I want to focuss on.

I just found it odd that I thought I knew a lot of what there is to know about yeast and I have not come across this until recently. While not applicable to brewing it is still worth mentioning in brewing books.

Kai
 
If you did do this, would it be a good starter, though? In How to Brew John Palmer talks about how close the conditions of the starter should match the beer (temp and gravity, mostly) so the yeast will be acclimated to your wort and ready to so their thing once you pitch them. Seems if the yeast have adapted themselved to metabolize ethanol, there'd be a big lag as they readapt to metabolize sugar.

Thoughts?
 
jrfuda said:
Seems if the yeast have adapted themselved to metabolize ethanol, there'd be a big lag as they readapt to metabolize sugar.
[\quote]

These were my thoughts as well. It may not provide any improvement over existing techniques.

Kai
Click to expand...
 

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