Two yeast packs in one starter?

Question

Assume one yeast pack in one starter results in double the cell count; i.e., 2x.

Would two yeast packs in the same exact starter result in double the cell count, i.e., 4x, somewhat close to 4x, or somewhat close to 2x?

Answer 1

Increasing the innoculation rate alone will not necessarily result in a linear increase in cells. You'll have twice as many cells now competing for the same amount of sugars and nutrients, they may not be able to do as well.

White and Zainasheff's Yeast has some empirical data about changing the innoculation rate by changing the volume of a starter, with a fixed 100bn cell White labs vial (around page 140-142). I'll not reproduce it all, except to say that there's an innoculation rate "yield curve", showing the number of new cells created for a particular volume and thus innoculation rate. It's roughly an inverted parabola with a flattened "top", with a yield factor around 3.4 at 200mn/ml, plateauing between 7-8 from 150-50mn/ml, then starting to drop back down to 6.5 at 25mn/ml, to 5.3 around 13mn/ml.

I would suggest using a starter calculator to play around and see what rates are computed when changing the pitch rate and volume, independently.