Originally Posted by duboman
So I think that here in lies the issue. Lets put aside the whole concept of pitch rate and focus on the second and somewhat more important topic of yeast health. Everyone speaks of and concerns themselves with ensuring proper pitch rate but very few look at the aspect of growing that pitch rate up with the most healthy yeast possible. Hence the desire to use a low gravity wort and proper aeration and reasonable temperature to produce their starters. Those that are less diligent will in fact produce proper pitch rate but perhaps not the most healthy yeast in the colony.
I believe this to also be the thought process behind the making of starters for dry yeast. Think of it as being a huge overpitch in a very small beer. Will you increase cell count and pitch rate? Yes, but will those cells be the healthiest? Perhaps not. Because you are pitching a product that is properly created to have everything it needs to ferment a reasonable gravity beer to start at 5 gallon batch size, by putting it to work in a low (1.030) gravity, very low volume of wort, the cells are not working to their most efficient potential and thus replicating in less than ideal conditions to achieve their maximum output, so to speak.
I agree that the focus needs to be on yeast health. That is exactly why I brought up the topic of yield factor with the starter. With liquid, pitching 100 billion cells into a 0.5L starter vs. a 1.5L starter vs. a 4L starter results in increasing amounts of yeast cells as the starters are made larger, but the yield factor peaks around 1.5L. The book essentially says that yeast grown at peak yield factor will result in the most, healthiest yeast. Lower yield factors indicate either there was either not enough food or the starter was too large for the colony, both scenarios resulting in unnecessary stress on the yeast, while the biggest yield factor would indicate the least amount of stress placed upon the yeast.
So this idea of getting the peak yield factor is really the thing to focus on if you want to grow your yeast colony in the most responsible way. This is why I think a packet of dry yeast can be used in a starter just fine, but care needs to be taken to make sure you hit the right inoculation rate to achieve the greatest yield factor. Therefore, if you are starting with 100 billion cells of liquid yeast, you would ideally want your first step starter to be 1.5L, thus growing your colony to 181 billion cells that are in peak health. I think many people jump straight to a 2L starter because it yields the magic number of 200 billion cells and the yield factor is only marginally reduced (from 7.7 to 7.6). By extension, if you are starting with 200 billion cells, you would ideally want to make your first step starter a 3L starter, thus keeping the inoculation rate the same as the example mentioned a moment ago (67 million cells per ml).
It is worth mentioning, though, that if 200 billion cells are inoculated into 3L of starter wort, the resulting number of yeast cells would be in the neighborhood of 360 billion cells. You really only need that many cells for a 5 gallon ale that has an OG of around 1.100 - this is a bigger beer than most people make, but if you are propagating with the intention of banking some of the yeast or if you are doing a 10-gallon batch, this could make sense. That is, of course, if the cost of making the starter doesn't outweigh the cost of just buying a 2nd packet of yeast. For the actor in our thought experiment, this scenario seems to makes sense.
Just as we can harvest the formerly-dry yeast from the beer in the end, we can harvest the formerly-dry yeast from a starter that has finished fermenting, and if care was taken to make sure the yeast had optimal growth conditions I just don't see how there is any harm to the yeast's health in doing so.