Minor thread hijack about starter gravity. I asked Chris White about this via email right before his yeast book came out (because I'm an impatient bastard)
Here is his reply:
Hello. Thank you for your comments and for using our yeast. To really eliminate the crabtree effect, you need to be down under 1.010, and slowly feed the yeast sugar. But 1.025-30 is still a good range, and I think it is a good compromise to good yeast physiology and good fermentation. So I think that is the best gravity, and brewers wort with grain, liquid, or dry malt are all good. Thank you, enjoy the book,
Let's work out the amount of DME needed to get below the Crabtree threshold using Briess Pilsen Light DME, which is specified as containing 14% glucose (www.brewingwithbriess.com/Assets/PDFs/Briess_PISB_CBWPilsenLightLME.pdf
). The Crabtree threshold is 0.3% glucose w/v. With Briess Pilsen Light DME, the Crabtree threshold lies at 0.003 / 0.14 x 100 = ~2.14% w/v, or an S.G. of a little more than 1.008. We need to stay below this value in order to maintain aerobic growth; hence, an S.G. of 1.008 should do it (0.02 x 0.14 x 100 = 0.28% glucose w/v). We can go lower; however, we are talking about a nutrient source that will be consumed fairly rapidly. Maltotriose and higher-order saccharides make up almost a third of Briess Pilsen Light DME. Many strains are limited in their ability to break the glycosidic bonds that hold the three glucose molecules in maltotriose together. Strains such as Windsor cannot do it at all, which is why it leaves a high terminal gravity.
In order to grow yeast aerobically, we need a way to maintain the carbon source (sugar) and the dissolved oxygen level at a steady state. This type of process is known as a chemostatic process. The device used by the big boys to produce dry yeast aerobically is called a bioreactor. Bioreactors propagate yeast aerobically in a continuous process where yeast cells are drawn off while nutrients and oxygen are added.
As an aside: a tower fermenter is a bioreactor in which beer is continuously drawn off of the top while nutrients are added at the bottom. Whitbread B (a.k.a. NCYC 1026, Wyeast 1098, WLP007, and S-04) was selected for use in tower fermentators (click on strain information on this page: https://catalogue.ncyc.co.uk/saccharomyces-cerevisiae-1026
). That's why it's the cockroach of yeast strains. Whitbread B is a seriously hardy yeast strain.