currently fermentatation of sugar feedstocks proceeds until the ethanol content reaches 12% at which point the yeast cannot live. then the contents
are distilled at a temperatiure which kills the yeast. so, either a dilute sugar solution must be used, or some of the sugar feedstock will be wasted.
also since the yeast takes 40 minutes to double, if a concentrated sugar feedstock was fermented, distilled and refermented several hours would be
lost while the new yeast doubled.
i was wondering if it might be possible to run a continuous process instead of the batch process where the ethanol water azeotrope was continuously
distilled at reduced pressure, until there was nothing left in the batch except water and yeast, or until the non sugar components of the feedstock
built up until the feedstock had to be renewed.
i guess i have three questions 1) what is the highest temperature yeast can be used at 2) what is the vapor pressure of ethanol water azeotrope at
this temperature and 3) will the yeast be harmed by this low pressure (i heard yeast needs oxygen to function).chemoleo - 5-6-2005 at 13:37
Your yeast doubling rate is a little high don't you think? It highly depends on the medium it grows in, the best I've seen is around 2
hours.
YOu might want to have a look at this website.
As to highest temperatures - it won't be much higher than 37 deg C. Vapor pressure - the vapor pressure is obviously higher than H2O else you
wouldnt get an Ethanol water azeotrope at 96% at 78 deg C.
The only way I can see a continuous process of ehtanol production to work is
1) make mutant temperature resistant yeast, and distill continuously (many fungi grow great at 80 deg C, don't know about yeasts though)
2) Bubble finely dispersed sterile nitrogen gas through the yeast/sugar/water suspension so as to remove ethanol, which is condensed elsewhere. Of
course you'd have to add water, and more nutrients, and remove cells to avoid the yeast reaching the growth plateau.
Not an easy task. Surely this has been tried, but I don't think it would be practial. Continuous life bioreactors are always a pain in the neck,
for reasons of sterility and adaption/evolution to species that produce less of the desired (which is either harm- or wasteful) product (ethanol).
[Edited on 5-6-2005 by chemoleo]Taaie-Neuskoek - 5-6-2005 at 14:54
For a contineous process I can recommend immobilised cells with alginate beads, really, really simple.
Waht you do basically is that you resuspend yeast cells to a total concentration 3% (sodium)alginate, then load them into a syringe, and drop them in
a 0.2M CaCl2 solution.
Load these cells into a column with a poreus plate, and flow a sugar solution with a bit CaCl2 added to it through.
With a bit of improvement and with the correct peristaltic pumps you can make a good amount of alcohol out of this, or even use them as batch
process...
The beads have a lifetime of 4000h, so that's excellent.
XXXXX, I can't answer question #2 but I'll try on #1 and #3. On highest temperature, it varies.
I use Alltech SuperStart which can withstand temperatures in the 90 F range. Some yeasts
don't like it that hot. SuperStart is a distiller's yeast that consistently produces 20%+ alcohol.
As for the question about oxygen, the yeast need some O2 during the aerobic phase in
order to multiply the yeast colony. Again, how much is needed depends upon the yeast.
During the anaerobic phase, the yeast break the sugar down into ethanol and CO2. I don't
know if yeast will survive under vacuum conditions as I've never distilled ethanol that way.unionised - 6-6-2005 at 13:33
From my home brewing experience, by the time the fermentationis nearly over, the yeast settles out. You could pour off the liquid and add sugar/water
to the yeast. Give it a shake and you should be back in business.
That way, you don't need to wait for the yeast to multiply so much.
BTW, I have seen some people in a hurry for a drink but worrying about a few hours seems extreme.
Continuous
MadHatter - 7-6-2005 at 10:57
A thought crossed my mind. Whiskey distilleries use their own proprietary strain of
yeast. Either they're recovering it or they're maintaining colonies outside the fermenting
and distilling process. Probably both. Yeast mutates afters so many generations, so a
fresh infusion of yeast is needed at some point to maintain the characteristics of the whiskey.
This wouldn't matter to producers of industrial ethanol as long as the yeast keep working.
I'd search for processes by any company that produces industrial ethanol - dentatured alcohol, gasohol, etc.
dead yeast?
hAzzBEEn - 26-7-2005 at 07:56
Quote:
From my home brewing experience, by the time the fermentationis nearly over, the yeast settles out. You could pour off the liquid and add sugar/water
to the yeast. Give it a shake and you should be back in business.
From my home brewing experience/research, I was under the impression that the yeast dies and settles to the bottom. Is this inaccurate? Is
there enough living yeast left to regenerate the fermentation?docberto - 26-7-2005 at 14:56
I believe that there are ale and lager yeasts that are separated by whether they are "top-fermenting" or "bottom-fermenting"
respectively. To do this method, it seems like you would need lager yeast, S. uvarum.ordenblitz - 26-7-2005 at 18:22
Both ale and lager yeast flocculate, (settle to the bottom) after exhaustion of available sugars.
Ale yeasts usually ferment faster and settle faster.
Yeast sediment is not dead at all but gone dormant, awaiting the next available food source. Too high an alcohol content will begin to kill them as
well as high heat.Fleaker - 2-8-2005 at 21:01
Yeast doesn't need oxygen to function: anaerobic fermentation, which is why we get ethanol. If anything you want to keep air out of the
mash/wert or else it will go rotten as other microbes take up lodgings.
I remember reading a book on distillation of spirts that mentioned most brewer's yeasts will function up until alcohol concentrations of around
21%. As far as the maximum temperature they will handle, I think that is species specific but I would imagine not more than 80C at the most.Ramiel - 3-8-2005 at 00:03
A brew going rotten is not affected overmuch by how much oxygen your brew has ‘access’ to. If your equipment and ingredients aren’t sterilized
satisfactorily, there will be infection in any case. You may find that the risk of infection is reduced when obligate aerobes can’t get oxygen,
however, in all brews, especially in systems which employ continuous distillation, or brew for a long time, one may find that versatile organisms or
even obligate anaerobes (I don’t know about that last one for sure ) will arise
from dormancy to ruin your day.
Correct me if I’m wrong, but if you were using a continuous distillation rig using those alginate beads, one would have to flush the system
periodically with oxygenated mash so that the yeast doesn’t die ‘of old age’. That is, to give the old yeasts a chance to reproduce once every
so often… could be wrong, but I find it pretty unlikely that yeast have lifespans of over 500-700 hours.Fleaker - 3-8-2005 at 17:38
I don't believe I ever claimed that oxygen would cause a brew to go rotten, but oxygen does have effects on ethanol (same reason why old
champagnes turn to vinegar).
Sterilization is an obvious necessity as all who work with microbes know all too well epck - 3-8-2005 at 18:12
I think a bacteria is responsible for turning ethanol into acetic acid, the Acetobacter Bacteria in fact. It is a aerobic bacteria hence the need for
O2. Here's the Wikipedia entry on acetic acid.
When you brew beer the wort (the boiled malt) needs to be well oxygenated when the yeast is first added so that a good vigerous growth of yeast is
obtained. After the yeast is well established it is desirable to keep O2 out of the brew for several reasons; to keep the yeast in anaerobic
respiration so that ethanol produced, to protect the molecules responsible for the delightful, delightful taste from oxidation and to help minimize
the threat of a bacterial infection.
However, I am unsure of the complete lifecycle of yeast. Will yeast keep reproducing in an anaerobic enviroment? I think so but I admit I am
guessing. However, if this is not the case it should not present a problem to introduce a well aerated wort on occasion but I think this will be
unnecessary. With the the immobilized yeast I have no idea. Do they keep reproducing? Is the new yeast immobilized as well?sparkgap - 4-8-2005 at 08:44
Let's just say that given a choice, S. cerevisiae would very much prefer an aerobic environment to an anaerobic one, although the reason
that fermentations are done with exclusion of air is that they shit alcohol (sorry, couldn't resist ) only when they're oxygen-deprived...
Now, to answer a question previously asked: yes, they'll keep reproducing in an anaerobic environment, as long as there's a facility for
them to be rid of alcohol and all the other nasties they'd rather live without... otherwise, they drown themselves in their shit...
sparky (^_^)gil - 14-1-2007 at 10:09
X dogberto:S. uvarum is wine yeast not lager.it's present on the skin of the grape (uva).
X hazzbeen: yeast sold fresh ,or dry,is the stuff collected at the bottom of the ferm. vessels.Dead or alive?
[Edited on 14-1-2007 by gil]
[Edited on 14-1-2007 by gil]Sauron - 14-1-2007 at 10:32
Vacuum fermentation is an old failure. Too much energy lost to reducing pressure and then having to pressurize the ethanol vapor to get it to liquify.
You're many decades late.
There are many yeasts on the market that will ferment to 16-18-20% not just 12%
You must allow the dead yeast to settle out completely before taking off the clear supernatant ethanol-water-sugar soln, if you have any yeast in the
still pot you will make furfural and spoil the taste of your ethanol.Sauron - 14-1-2007 at 10:41
If you want to ferment sugar to make vodka he has excellent products and a lot of good information.roamingnome - 14-1-2007 at 10:51
im considering pumping the mash through a tube, heating said tube, and through an oil burner type nozzel for a flash type still. Use multiple nozzels
even.
I need to filter the actively growing yeast out first of course. How small are these?
Can I use a super fine mesh screen, Ive seen some real quality meshes for aqua culture use and stuff... The active yeast wad can be used for many
healthy things, like food and science.gil - 14-1-2007 at 12:17
Tanks SA. Nice hook-up!Top info.Sauron - 14-1-2007 at 17:59
You work under clean room conditions? The same media that are used here are beloved of various common bacteria. Anyone seriously into fermentation
needs a good microbology lab in house just to stay on top of competing infections. Cleanliness is vital and let me tell you, fermenting is not
conducive to that. Mold is also a huge problem. Various biocides are used in the industry to mop floors, scrub walls etc to beat that down.roamingnome - 14-1-2007 at 20:05
looks like i need some turbo yeast from partyman, sweden. im working up to liquid culture for trichoderma reesei and algea strains etc.... you
dont want to pay top dollar for a strain and not have everything ready for its continued growth
if i could just have the media bottles and nalgene culture equipment that i had to throw in the trash in one day at the biotech company i was at, i
would be set for life! its incredible how much is thrown away... its sadening
how many microns are growing yeast? theres diatomaceous earth to clean up your fermentation mash. but ....these stocking mesh bags are appealing,
well its time to just do it... i know..gil - 14-1-2007 at 20:50
Kieselghur work fine,it's free and is a renevable resource.i'm harvesting it once,max twice a year and that does me for my brews,lab and grow needs.pneumatician - 23-9-2020 at 18:16
Wait untill alcohol rise to max.
destil etanol with liquid nitrogen
continue with fermentation
yeast not support heat, but cold? if yes, here is the solution.
) will arise
from dormancy to ruin your day. 
) only when they're oxygen-deprived...