Adding more yeast after 12 hours of fermentation?

[thefost]

Made a batch of IPA yesterday, ended up at about 6 gallons of 1.062 wort. I put a lot of effort to make sure I did everything exactly right, but of course I messed up and forgot a starter.

I pitched a two month old bag of Wyeast in the fermentor and aerated well with pure oxygen. My question is which is the optimal option: Should I leave the beer as is, or should I pitch another bag of Wyeast 12 hours into fermentation?

Or perhaps it doesn't even matter at this point and the beer should come out exactly the same.

 

[david_42]

I think it will be fine, as-is. The only thing a starter does is reduce the growth period for the yeast, which means a bit more lag before the fermentation phase starts. If your batch is already fermenting, don't worry.

 

[philosofool]

I think it will be fine, as-is. The only thing a starter does is reduce the growth period for the yeast, which means a bit more lag before the fermentation phase starts. If your batch is already fermenting, don't worry.

I wouldn't say that this is the only thing that a starter does, but I think I would agree with the conclusion. Two month old yeast is actually still pretty fresh for the perfectly prepared packaged yeasts we're dealing with. I'm pretty sure calculators of viability are based on the age of re-harvested yeast, not the packaged stuff.

In any event, after 12 hours, the additional yeast you add have no oxygen to work with, which will be bad for them. You could add more oxygen at that point, but I don't see why you need to add fresh yeast to an active fermentation--the yeast in there will start to multiply happily if you just let them go back to aerobic metabolism. I'm not recommending more oxygen, because I really can't say how that would cause off fermentation by products, but I just don't think fresh yeast is your answer at this point.

 

[thefost]

I agree, it probably wouldn't have helped so I just left it as is. Vigorous fermentation took off within 18 hours so thats a good sign. Thanks guys