I wrote before about making a yeast extract at home and I just realized that I never followed up on that. Turns out it’s actually a very good yeast growing medium. It’s been used in about 1:1 proportion with DME based starter to make a starters and the results were just unbelievable. At first the fermentation was so vigorous on a stirring plate that there was actually foam billowing out of the flask. When I first counted I thought there was something wrong and did the dilutions over again and ended up with the same counting results of up to 1.6E9 ml-1 i.e. about 1.5 trillion cells in a 1 liter starter. And that’s assuming 80% of the cells seen were viable (don’t feel like staining with trypan blue). It should probably be pointed out that this was tested with Brettanomyces. Since then the proportion has been cut to about 1/10 of the total volume in a usual DME based starter and seems to be working quite well.
Another thing to confirm the nutrient richness of this concoction is that I tried making plates with this extract. As some of you know if there are too much goodies in the agar it won’t solidify (for example high gravity wort). In the end I diluted that extract 10-fold and used twice the amount of agar and they were still too soft or not solidify at all.
From this I’d conclude that such yeast cake utilization is very nice for growing more yeast if you can do it. Perhaps there is something wrong with my calculations, but judging by the yeast sediments at the flask bottoms at least it’s way better than just DME based starter.