Out of curiosity - Denny, what yeast strains have you encountered increased ester production when overpitching?
My experience, as a lazy and cheap brewer who tends to use yeast cakes over and over, is that of the others who have posted here. That is, English and weissbier strains benefit from underpitching to achieve the ester character in the final product. Having known you on various forums for many years, Denny, I am fairly certain that your experience on overpitching is not drawing on British bitters or hefewieizens.
In fact, this subject seems to come up with some regularity, and as far as I am aware of, only you and Dr. Cone have had excessive ester production resulting from overpitching. Which makes me wonder if it is 1450 thing. Or maybe an APA/IPA thing, the hop debris in the trub is causing some effect.
My experience: besides the above, overpitching results in greater attenuation, especially with ale yeast. Lager yeasts, I think you can pitch and pitch again on top of yeast cakes with no adverse affects, as long as you keep it clean. I have gone up to 7 times with pilsner yeasts with no noticeable off-tastes.
Here’s a bit more research suggesting pitching rate has little effect on flavour:
Appl Microbiol Biotechnol 2009, Impact of pitching rate on yeast fermentation performance and beer flavour.
From abstract:
*The influence of pitching rate on aroma compound production was rather limited, with the exception of total diacetyl levels, which strongly increased with the pitching rate. These results demonstrate that most aspects of the yeast physiology and flavour balance are not significantly or negatively affected when the pitching rate is changed *
I think it’s important to make the distinction that while pitching rate alone may not affect flavor as much as people think, it is related to yeast growth and yeast growth is related to other contributing variables in fermentation, i.e. Aeration, etc.
So it’s simultaneously true and not true to say pitching rate doesn’t matter
Here are the results from another published paper. This paper found a slight increase in ester production with higher pitch rate:
A near doubling of pitch rate causes a 3% rise in one ester and 7% rise in another. Perhaps it’s enough to have a significant effect on flavour but changes this small could equally be a measurement error.
Institute of Brewing & Distilling, “The effect of pitching rate on fermentation, maturation and flavour compounds of beer produced on an industrial scale”
Effects of pitching rate aside, I’ll go back to post #2 and agree with bayareabrewer.
On the homebrew level, it’s pretty hard to overpitch. You need to do something deliberate such as pitching an entire yeast cake, growing a huge starter, or pitching many packs of yeast.
As far as does it matter? As Keith pointed out, pitching rate matters most with respect to consistency. All other things being equal, you’ll need to pitch a similar amount of yeast to consistently repeat the same beer.
At the homebrew level, such consistency isn’t always an issue. It is for some of us. Not all of us.
Overpitching can result in yeast autolysis but is most evident if you are reusing your pitching yeast. If reusing yeast and overpitching in each batch there will be very few new generations of yeast created, and the older generations of yeast will eventually become tired and sluggish.
