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.

 

[MileHighBrewer]

yeast cake = GIANT starter

 

[boydster]

You had no growth phase. Usually when people reuse a yeast cake, they remove a portion of it to make sure there is still a healthy growth phase. If you are remaking the same beer, you only need about 1/4 of the previous cake.

 

[g-star]

Pitching directly onto your yeast cake is almost never good practice:

https://www.homebrewtalk.com/f163/why-not-pitch-your-yeast-cake-166221/

 

[ultravista]

It was the same beer, the second batch being more efficient (perhaps due to mash water ratio).

Lag time was non-existent.

 

[BigFloyd]

Hmmmmmmm..........4-5 times the amount of yeast cells needed plus 83*F wort. I'm not surprised that you saw an uber-short lag. Very likely it will taste different than batch #1.

 

[tagz]

You'll have a nice comparison experiment, regular pitch/regular temp vs over pitch/high temp. Two variables isn't ideal but it should prove interesting. Let us know what you think.

 

[HopOnHops]

When you buy yeast to a certain degree they will be malnourished. They will consume internal nutrients to stay alive from the time they leave the yeast house to your brew house. To get the yeast in top shape people typically make a starter which is essentially a practice run at fermenting. The fermentation cycle does 2 things to yeast; grows their population and builds up nutrients within the yeast.

So pitching onto a yeast cake you are essentially unleashing yeast in their prime to annihilate your wort. You will notice a shorter lag time, overall fermentation time, and attenuation. Each will typically increase with generation of reuse due to the natural selection you are performing in your beer.

There are tons of research telling you not to picth onto a yeast cake. Some key ones that convince me not to do it are crap leftover from your previoue brew going into your next and over pitching. You will learn all this in due time, good luck.