Aeration Schmaeration

A bit of Science - we look at the relationship between aeration of wort and healthy yeast cell count

A bit of background first - we're in the process of setting up a brewery in the storage area at the back of the shop (more of which anon). One of the pieces of kit we're looking at investing in is an oxygenation system to ensure an adequate supply of O2 for our yeast pitch. This typically consists of an Oxygen bottle, regulator, a couple metres of high pressure hose and an inline oxygenation stone to dissipate the O2 into the wort.

However there's not a single tenet about brewing that hasn't been disputed somewhere on the internet and I came across a few posts advocating the use of an increased yeast pitch instead of wort oxygenation. This kinda makes sense as Oxygen is only required for the first stage of fermentation - the mother-daughter replication of the yeast cells - and not the subsequent conversion of sugar into alcohol.

Our experiment will be to ferment two identical batches of beer, one with 1g per Litre US-05 yeast and no aeration, the other with 0.5g per Litre US-05 yeast and a decent aeration. As we do not have an Oxygen bottle yet, we're going to use an agitator rod powered by an electric drill instead.

The wort we used was from the Panhead wort packs brewed on the 6th of December, so absolutely identical. Both fermenters were filled with 16 Litres of 1.058 wort. One was vigourously agitated and 8g of US-05 added. The other fermenter was filled gently and 16g of yeast was sprinkled on the top. Both airlocks showed signs of 'pressure' after 4 hours. Results and observations to follow.

2014 12 11 14.44.27

 Cheers

 Update - 16th Dec 2014

The non-agitated fermenter was a little quicker off the blocks, with a little pressure in the airlock after 6 hours and a slightly quicker rate of CO2 at 16 hours post-pitch. A gravity reading at 2 days was an identical 1.038 (down from 1.058) and a further gravity reading at 4 days 20 hours had the agitated fermenter slightly ahead, 1.014 Vs 1.015.

 Update - 21st Dec 2014

Both fermentations have nearly finished, giving a final gravity of a whisker over 1.012.  I suppose we'll have to settle this the old fashioned way - with a taste test. Tune back in after a couple of weeks.

 Update - 25th Dec 2014

Samples from both fermenters proved inconclusive (both Kerry and I sampled) so I put a couple of bottles of each away before kegging. We will do a blind triangular test in a few weeks.

Final Update - 3rd Feb 2015 - Taste Test

I subjected Kerry to a triangular taste test a couple of days ago. Two samples from one fermenter and one from the other. First he had to identify the 'odd one out', then decide which was best. As expected, there was little difference in taste between the two methods but when they warmed up there was a hint of Acetaldehyde in the over-pitched, non-agitated sample.

Conclusion:

Aerate the wort using whatever method you like; raw O2, sanitary air pump, agitator, vigourous shaking. And use the pitching calculator from this page to calculate the amount of dry yeast required.

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