Pitching Rate Experiment – Tasting

After about a week of being carbonated at room temperature and a few days in the fridge I tasted the beers fermented with different pitching rates. All beers carbonated well.

But first a few stats that I also collected: pH an foam stability. Below in bold:

test name A B D C E

stating extract 13.1 Plato
attenuation limit 80.0%

yeast strain WLP830 from slant

yeast source Bo Pils FFT

yeast age 2 days
fermentation type still, airlock, in 500ml flask

fermentation temp 18 C
starting O2 7.2 mg/l
pitching rate 32 23 15 9 2 M/ml
extract drop per day 1) 3.5 3.7 3.7 3.0 2.8 Plato
final extract 2.7 2.7 2.7 2.8 2.9 Plato
attenuation delta 0.6% 0.6% 0.6% 1.4% 2.1%

yeast growth 36.0 30.7 37.5 33.9 29.3 B
growth per extract 0.77 0.66 0.81 0.72 0.63 B/g
pH 4.28 4.37 4.50 4.43 4.60

foam 7:06 12+ 11:20 12+ 10:25 min

The pH of the beer behaved as expected: The more aggressive the fermentation the larger the pH drop and the beer with the most aggressive fermentation was the one with the highest pitching rate. I was a bit surprised by the magnitude of the beer pH difference.

Foam stability is where I pour the beer straight into a Koelsch glass until the foam reaches the top and then I measure the time it takes for the layer of bubbles to collapse, break and reveal the surface of the beer. These numbers are not very repeatable and can be very random. Everything above 7 min is pretty good. The test is designed to detect major deficiencies in foam stability.

The 5 beers a few minutes into the foam stability test

The 5 beers a few minutes into the foam stability test

As for the taste differences, all beers tasted very similar. I did the tasting knowing which beer was which and it appeared to me that beer A, the one with the highest pitching rate, had a more estery taste and aroma than beer E, the one with the lower pitching rate. The lowest pitching rate beer seemed to have the cleanest aroma but also appeared more bitter and exhibited a thinner mouthfeel.

The literature reports that ester production is connected with yeast growth and the more the yeast is able to grow the less it will produce esters since the ester precursor Acyl CoA is used for yeast growth. However, the amount of yeast sediment produced by each fermentation suggested that the most yeast growth happened for the beer with the highest pitching rate.

In the end, this is just another data point for the effects of pitching rate on fermentation performance and beer quality.


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