Yeast Populations

When yeast reproduce, will they continue to reproduce until they have reached a population capacity level, or is it just based on time they are in a reproductive stage? Basically I guess I am wondering, if you made a starter from say 1 vial of WL and you made another from half a vial, would they both have the same population when the fermentation was over?

The yeast will continue to divide essentially until they run out of fermentables (after a certain number of generations, this may stop being the case). So if you made a starter of the same starting gravity, and pitched half the yeast in one compared to the other, you will end up with the same amount of yeast in the end (assuming ideal fermentation conditions), but it will take a little bit longer.

That's the reader's digest version.

I think yeast propagate until the oxygen supply has been depleted, then they swith into anerobic mode and produce alcohol and co2. So if you used half a vial I don't think you will end up with the same amount of yeast. This is why a stirplate is used, the constant oxygen supply allows yeast to propagate to greater numbers.

Iordz said:

I think yeast propagate until the oxygen supply has been depleted, then they swith into anerobic mode and produce alcohol and co2. So if you used half a vial I don't think you will end up with the same amount of yeast. This is why a stirplate is used, the constant oxygen supply allows yeast to propagate to greater numbers.

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Correct, that's why I added under "ideal fermentation" conditions

Yeast will repoduce until they run out of nutrients and reserves for growing a daughter cell. This also happens during the anaerob (fermentation phase) as you will notice by the gowing yeast cake during fermentation. During the initial aerob phase they are building reserves (of sterols for instance) which they will live on during the fermentation. Growth basially slows down as fermentation slows down.

A stir plate gives you more yeast growth b/c it keeps more of the yeast in contact with the wort. Unless you have a really nice and deep vortex going, there won't be up O2 uptake into the starter.

Kai

The main reason I am asking, is because I'm trying to determine how much I should pitch from a starter. I am planning on making an IPA from WLP 045 with 6lbs of LME and a few pounds of specialty grains steeped in. I'm not sure what the OG will be. I am planning on making a large starter (5 pints) so that I can save some for future batches. After reading some of the starter info, I'm guessing that I would like to ideally pitch around 200-250 billion cells. Basically, I guess I'll pitch 1 - 1.5 pints of the starter..

Check out mrmalty.com for starter sizes. A good rule of thumb for gravity of starters is 1 cup of water with 1 oz. of DME = 1.040 SG