Yeast cake question

So, I've been seeing some people talking about using the same yeast cake for multiple batches during fermentation. What exactly is this? My thinking is that when you brew two batches that use the same type yeast, after your boil for the second batch, you pour it in your primary fermenter overtop of the sediment in the bottom of the fermenter that is left over from the first batch. Is this correct? If so, what is the advantage of doing this? Saving the $4 or so another thing of yeast would cost?

A few things... free yeast, a GREAT yeast starter, no cleaning the carboy... You can save over $7 for liquid yeast!

Brewpilot

Yep, you got it. I've done it once and plan on doing it again next week. As you noted one big advantage of doing this is that you can get two (or more) batches of beer for the price of one dose of yeast. I think an even bigger advantage is that you are pitching the proper amount of yeast, and that they are primed and ready to go. No starter required. The one time I did this I had an extremely vigourous fermentation. There was krausen in my airlock, and the lid on my bottling bucket was covered with hop residue. This was a lager, which generally don't have really vigourous fermentations.

I did this recently, putting a stout onto yeast of a pale ale.

The fermentation took off almost immediately...and as mentioned...less cleaning!

I like the postponing cleaning idea. I think I'm going to do this on my next batch. How many times is it safe to reuse the same cake?

Id use it twice without washing it, if you wash the yeast, up to say 4? Without washing you will have larger and larger ammounts of trub. Id do it twice myself.

Brewpilot

I'm going to be pitching my IIPA on top of the yeast cake from my Blonde Ale next week. I can't wait to see a mega-massive fermentation! But yeah, I'm going to dump it after that. I figure two uses is pretty good, and I'm too busy/lazy to try washing and saving yeast cultures so far.

no cleaning the carboy...

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that's the biggest problem i have with reusing the yeast cake. personally i'd pour off the slurry. let it settle out and then use it...