Why Quick Start on Yeast Cake?

[ultravista]

I brewed batch # 1 on 03/24, left it on the yeast at 42-44F for the last two weeks to clear. The beer was on the yeast cake (WLP530) for a month.

Today I brewed batch # 2. Transferred batch # 1 to the keg, put it back into the refrigerator, and worked on # 2. Same malt bill, hops, etc.

Due to an error on my part, the beer entering the carboy was about 83F. I hit it with O2 for about 60 seconds, and let it settle before putting it into the refrigerator.

Within 10 minutes of the 02, and approximately 20 minutes after transferring from the keggle, it began to start fermenting. I thought it was residual O2, or perhaps CO2 from the cake. Nope, it started fermenting.

Is this common for pitching on a cake, near immediate start. Lag time was 20 minutes or less.

[brewinhard]

Yes that can be pretty common especially depending on the gravity. If it was a lower gravity, then the yeast will quickly get to work especially with enough oxygen. Not always the best idea to use the whole yeast cake though as it contains many dead cells (most likely with mutations) along with proteinaceous material (trub) from the first fermentation. Plus as you observed, the fermentation takes right off (minimal lag time) which means the yeast did not go through much of a growth phase.