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Kaiser · 09-09-2012, 10:50 PM

One of the reasons why you want to pitch a lot of yeast into high gravity beers is simply this:

When yeast experiences an increased alcohol level in its environment it wants to build stronger cells walls. That was shown in experiments where the yeast had access to oxygen at that time. In brewing fermentations, however, this oxygen is not available and all the yeast has are its sterol reserves. If the yeast has undergone lots of growth up to this point these sterol reserves will be depleted since they are divided between mother and daugther cell at budding time. This growth can be limited with larger pitching rates and thus the individual yeast cells will be better prepared for the high alcohol environment

dstar, how much variability in yeast growth compared to Jamil's calculator have you seen? I expect that there is actually a lot and the limited data I have supports that. I have not yet had a chance to run a series of controlled yeast growth experiments. All I have done so far is track yeast growth in many of the starters I made and the growth per extract ranges from 0.8 all the way to 1.7 Billion cells per gram for starters on a stir plate covered with foil. There is no apparent correlation with the initial gravity of the starter or the initial cell density.

Kai

**dstar26t** · 09-13-2012, 06:23 PM

Quote:

Originally Posted by Kaiser

dstar, how much variability in yeast growth compared to Jamil's calculator have you seen?

Usually get ~75% of what Jamil's calculator predicts. One time I got 51%. I've been plugging in 25% additional cells needed lately and get what I need out of the calculator. I use foil over a flask on a stirplate. I'm going to re-design the stir plate so I can get more agitation without throwing the bar. I tried pumping sterile air into the headspace continuously but that didn't help. I may try what you did with the stone in the starter wort but that is more stuff to clean.

suregork · 09-26-2012, 02:32 PM

Here are links to two quite recent scientific articles (they should be free) regarding high gravity brewing:
http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2007.tb00259.x/abstract
http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2011.tb00472.x/abstract

The first is a study on the influence of pitching rate on flavor compounds and fermentability, while the second one (written by my boss by the way

) is a review on techniques to improve high gravity brewing (you might find something worthwhile in there)

EDIT: <-- Why the heck does the forum software think I'm from Seattle, Washington even though I have entered a completely different location

Kaiser · 09-27-2012, 02:31 PM

Tanks suregork.

On the topic of the accuracy of the pitching rate calculators that are out there, I’m in the middle of an experimental series where I add various amounts of yeast to roughly the same volume of the same wort and determine yeast growth per gram of extract on a stir plate.

So far the results show only a weak correlation with the curve that is used for Jamil’s and Wyeast’s pitching rate calculators. At an initial pitching rate of 50-100 M/ml the results are close to the calculators with ~1.4 B/g but below and above that they differ vastly. At very low picthing rates I still get ~1.4 B/g but at very high pitching rates (200-300 M/ml) the measured yeast growth drops to ~0.5 B/g while Mr Malty predicts better growth than at 100 M/ml. This makes sense since more of the sugar is used by the larger number of cells before sugar is used for actual growth.

I’ll publish some data once I have a few more data points. The inherent error in cell counting makes it necessary to have lots of data points in order to draw meaningful conclusions.

Kai