My presentation at the NHC today was very well received. Yeast growth in starters does interest a lot of brewers and I had a lot of new data to present. Now that I finished the presentation I can devote more time on experiment documentation here on braukaiser.com.
A copy of the presentation can be found here.
Kai, thank you very much for sharing your NHC presentation. Great source of knowledge put together on some slides.
Had to smile as I read “Sonnenleiter” on p6. I actually know B. Sonnleitner and had him as a professor during my undergraduate studies. He basically taught me the principles for my yeast kinetics post: http://eurekabrewing.wordpress.com/2013/03/01/a-glimpse-into-yeast-growth-kinetic-models/
Thanks. That’s a very nice post on yeast growth kinetics that you have on your blog. It’s very similar to what I read in Kurz’s paper. Unfortunately I have not been able to apply these models to home brewing starters because it requires coefficients that are different between different strains or depend on the equipment being used. One such coefficient is the O2 uptake during propagation. It ca easily be measured in a chemostat but in a stirred Erlenmeyer flask capped with foil the O2 update that can be expected is an unknown.
Thanks for reading my post. Some coefficients might indeed be a problem on home brewing scale. I actually work on applying my different Monod models on unstirred yeast starters for a start but don’t have enough experimental data yet to quantify some of the coefficients. The remaining coefficients will be quantified by iterative approaches. However, this project is actually put on hold due to lack of time. Stirred starters are yet a complete different story. My Monod model for this case is not yet finished and might take some time to dial it in with some of my chemostat data I have from my undergrad studies.
I kind of expect some variations between strains and the experimental setup as well. But one has to start somewhere, right?
I attended your talk at the conference and enjoyed it very much! Thank you for publishing your findings.
Thanks. I’m glad you liked it.
It appears that in this presentation and based on my use of the ptiching rate calculator on brewersfriend.com that when using a stirred started, innital pitch rate does really effect potnental growth as long as you are below about 1.4B/g. Would you say this is correct?
If so, that would mean that stepping up a starter (even from something as small as a slant) would not really be necessary. You could just pitch a tiny amount of yeast into an appropriately sized start to reach your necessary cell count. I haven’t seen a post where you address this specifically, but would you say that is accurate?
For propagating from a slant or small amount of yeast it is advisable to step up in order to keep the initial pitching rate large enough such that the yeast can outcompete other microbes. but when starting from a vial or smack pack it should not be necessary. the work of others indicated that there is a distinct optimal pitch rate for growth. I suspect that this work is not valid for stirred starters. With an optimal pitch rate it appears that there is also an optimal step up schedule for starters.
Twice so far I tried a series of experiments to test that theory but for some reason the yeast in some of the experiments started flocculating making counting difficult. I hope that I’ll eventually get that data.