When brewing, how little yeast can you get away with? If I use 1 packet of dried yeast for a bathtub of apple wine, won't it just multiply until either the sugar runs out or the 14% alcohol kills the yeast? If not, what's stopping it?
Why is lots of yeast even needed
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Kokopuff829
Well-Known Member
It's better to have a good amount of yeast because if not they can be stressed out and create esters. You can get away with minimum yeast but why take the chance of problems with fermentation and off flavors when you can just give it a healthy amount if yeast.
I brought this up in the Fermentation area....what I found out is that unlike wine fermentation where esters are usually a good thing, in beer making you want to minimize them. One good way is to have a sufficient yeast population right from the start.
So this makes pitching rates much more significant in beer making. In wine making you only need 1g/gallon and everybody uses dry yeast...not so in the beer world.
You also want the yeast to become the dominant critter as fast as possible to reduce the risk of infection.
But I'm thinking you could do your apple wine example no problem with one packet of dry wine yeast
Just clean the ring from around the tub first !!
So this makes pitching rates much more significant in beer making. In wine making you only need 1g/gallon and everybody uses dry yeast...not so in the beer world.
You also want the yeast to become the dominant critter as fast as possible to reduce the risk of infection.
But I'm thinking you could do your apple wine example no problem with one packet of dry wine yeast
Just clean the ring from around the tub first !!
JonK331
Well-Known Member
Yeast only reproduces during the aerobic phase. Once the O2 is used up the yeast stop reproducing and start consuming the sugars. There's a limited amount of O2 that can be dissolved in liquid so once it's used up that's it, no more reproduction.
I'm pretty sure there is a form of anaerobic reproduction in which they use reserves.... but I'll need to find citation.
While this doesn't point directly to my discussion, this study does show that anaerobic reproduction is possible, even in a medium not easily utilized.
Sonderegger M, Sauer U, Evolutionary engineering of Saccharomyces cerevisiae for anaerobic growth on xylose. Appl Environ Microbiol. 2003 Apr;69(4):1990-8.
Sonderegger M, Sauer U, Evolutionary engineering of Saccharomyces cerevisiae for anaerobic growth on xylose. Appl Environ Microbiol. 2003 Apr;69(4):1990-8.
Oxygen is used during the lag phase, not the exponential growth phase....that's why we don't add O2 once fermentation shows visible signs.
From Wyeast:
Log Phase
The log phase is a time of exponential growth of the yeast culture. The preparation the yeast made during the lag phase allows rapid multiplication of cells and consumption of sugar. Yeast reproduce asexually by budding; the adult cell forms a daughter cell that is an exact genetic copy itself. Nitrogen, amino acids, nutrients, and sugar are consumed while the cells are reproducing.
Many of the significant aromatic and flavor compounds are by-products of cell growth and are produced during the log phase. Many large breweries try to limit the amount of yeast growth by pitching larger quantities of yeast and therefore minimize ester synthesis. Keeping fermentations cold also limits ester production by limiting the rate of growth.
From Wyeast:
Log Phase
The log phase is a time of exponential growth of the yeast culture. The preparation the yeast made during the lag phase allows rapid multiplication of cells and consumption of sugar. Yeast reproduce asexually by budding; the adult cell forms a daughter cell that is an exact genetic copy itself. Nitrogen, amino acids, nutrients, and sugar are consumed while the cells are reproducing.
Many of the significant aromatic and flavor compounds are by-products of cell growth and are produced during the log phase. Many large breweries try to limit the amount of yeast growth by pitching larger quantities of yeast and therefore minimize ester synthesis. Keeping fermentations cold also limits ester production by limiting the rate of growth.
They definitely can and do reproduce anaerobically, but it's not optimal for making tasty beer. This is a stressful process on the yeast, during which all sorts of weird tasting compounds are created which can flavor your beer oddly. Oxygen is definitely the superior reducing agent, forcing the yeast to use other ones to complete their metabolism and reproduction is not friendly to them.
By pitching the correct amount (lots) of healthy yeast, we are ensuring that they have to do this as little as possible (ideally not at all) so we get the best tasting beer possible. An underpitch is a sure way to piss off your yeast and they have no qualms about messing up your beer if provoked.
By pitching the correct amount (lots) of healthy yeast, we are ensuring that they have to do this as little as possible (ideally not at all) so we get the best tasting beer possible. An underpitch is a sure way to piss off your yeast and they have no qualms about messing up your beer if provoked.
The least amount that I've read used commercially is 5 million cells per milliliter. That's right about 5 grams dry yeast or one vile/smack pack per five gallons on a homebrew scale.
Some yeast use more oxygen than others. At least 40% of the oxygen they use is scientifically unaccounted for. Dry yeast do not need any more oxygen because they are dried at peak sterols.
Some yeast use more oxygen than others. At least 40% of the oxygen they use is scientifically unaccounted for. Dry yeast do not need any more oxygen because they are dried at peak sterols.
Don't confuse reproduction with respiration. There are 3 basic types of cell respiration; Aerobic respiration, Fermentation, and Anaerobic respiration. It's all about who's accepting electrons. Remember the Glycolysis->Oxidative decarboxylation of pyruvate->Kreb Cycle from biology class? Without oxygen, pyruvate goes through fermentation, the waste products being ethanol and CO2...and NAD+ to re-enter the glycolysis pathway...not a very efficient path for energy production but we're after the ethanol, not ATP
Don't confuse reproduction with respiration. There are 3 basic types of cell respiration; Aerobic respiration, Fermentation, and Anaerobic respiration. It's all about who's accepting electrons. Remember the Glycolysis->Oxidative decarboxylation of pyruvate->Kreb Cycle from biology class? Without oxygen, pyruvate goes through fermentation, the waste products being ethanol and CO2...and NAD+ to re-enter the glycolysis pathway...not a very efficient path for energy production but we're after the ethanol, not ATP
We're talking more about reproducing under anaerobic conditions because of the stress it puts on the yeast before real fermentation starts. It takes a lot of energy to grow and divide, and that energy needs to come from somewhere. You're absolutely right, though.
The short, less technical explanation is that your beer can develop all kinds of off flavors due to underpitching.
e.g. acetaldehyde, diacetyl, DMS, esters, fusel alcohols, vegetal aroma/flavor can all result from this.
e.g. acetaldehyde, diacetyl, DMS, esters, fusel alcohols, vegetal aroma/flavor can all result from this.
You'll also increase the chance of infection by underpitching. Regardless of how well you sanitize some things you don't want it you beer, will get in there (a lot of them come off of you, and you don't really want to sanitize yourself!).
When you pitch an adequate amount of yeast, they take over and make a hostile environment for most critters to live in. They use up all the oxygen, create alcohol and eat food so fast most everything else just can't keep up. That gives you some buffer room so that even if a few thousand spores from some other bug make it in the wort (and the always always always will) they get out competed and die before they do any damage.
When you pitch an adequate amount of yeast, they take over and make a hostile environment for most critters to live in. They use up all the oxygen, create alcohol and eat food so fast most everything else just can't keep up. That gives you some buffer room so that even if a few thousand spores from some other bug make it in the wort (and the always always always will) they get out competed and die before they do any damage.
Enjoy your poor tasting, underattenuated beverages!
