Going to reuse yeast for the first time...advice?

I have 2 carboys full of beer that finished fermenting a few weeks back. I plan on brewing this weekend, and both carboys have the yeasts I need (California & Hefe). Do I just harvest the trub, throw in some DME, and put it on a stir plate? Any tips are appreciated!

Search yeast washing. This is the basics... https://www.homebrewtalk.com/f163/yeast-washing-illustrated-41768/

You can certainly harvest/wash the yeast...but, recently I transferred from primary to secondary and then from my boil kettle onto of the "used" yeast cake. I had excellent fermentation with both brews. Maybe I got lucky, as I'm sure someone will let you know why you shouldn't do what I just suggested. It was the first time I used the same yeast, and I had great results this time; but I wouldn't do this more than once.

Jdk261 said:

You can certainly harvest/wash the yeast...but, recently I transferred from primary to secondary and then from my boil kettle onto of the "used" yeast cake. I had excellent fermentation with both brews. Maybe I got lucky, as I'm sure someone will let you know why you shouldn't do what I just suggested. It was the first time I used the same yeast, and I had great results this time; but I wouldn't do this more than once.

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Yup, I've done that a few times. Right after I transferred from carboy to keg, I filled the carboy with cooled wort right on top of my settled yeast/trub. The beer started fermenting within a few hours, and it turned out great. Maybe the scary trub affected it in some way, but I couldn't taste anything bad each time I did this method.

I've also simply poured the yeast/trub from carboy into a sterilized mason jar, sealed it up, and put it in the fridge until the following weekend. On brew day I took it out of the fridge, dacanted, let it warm up during brewing, then pitched it. It took off pretty quick - probably 4-6hours, and was always a strong ferment and produced good beer when I did it.

Contamination is the only thing to worry about. I wouldn't do this more than a few times in a row with the same yeast - but it's a great way to save some money.

I have also done this with good results when going from a 1.040 beer to a 1.065+ beer. Pitch on the cake, no problem especially if the beer is bigger/darker. I wouldnt do it more than once though. That stuff builds up THICK.

So, if i've got this right, it sounds like all i need to do is rack the beer in the carboy, and then pour cool wort over the trub, and away she goes?

jdlev said:

So, if i've got this right, it sounds like all i need to do is rack the beer in the carboy, and then pour cool wort over the trub, and away she goes?

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Yup.

jdlev said:

So, if i've got this right, it sounds like all i need to do is rack the beer in the carboy, and then pour cool wort over the trub, and away she goes?

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Correct. You should have no problems as long as the first batches aren't hoppier or darker that the wort that'll be pitched onto their yeasts. Also, this practice isn't recommended if the yeast was first used to ferment a brew with a very high OG, but I'm assuming this wasn't the case if the yeasts are cali and hefe.

Using the entire yeast cake would be considered by most brewers to be overpitching. You want the yeast to have to reproduce to take care of your new batch. I think the Mr. Malty calculator can tell you how much slurry to use.

My rule of thumb is about a cup of slurry (depending on the beer) as opposed to the whole yeast cake.

I was going to divide the slurry in one carboy between 2 6g carboys.

jdlev said:

I was going to divide the slurry in one carboy between 2 6g carboys.

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This sounds like a reasonable plan. If it were me I'd just make sure a full cup of slurry got into each with good white yeasties.

osagedr said:

Using the entire yeast cake would be considered by most brewers to be overpitching. You want the yeast to have to reproduce to take care of your new batch. I think the Mr. Malty calculator can tell you how much slurry to use.

My rule of thumb is about a cup of slurry (depending on the beer) as opposed to the whole yeast cake.

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I'll second that! Clean that dirty fermeter and add a measured amount of yeast.

Assuming you had a reasonable pitch at the beginning of fermentation, the complete yeast cake at the end of fermentation will contain roughly 4X the recommended amount for correct pitching of a beer of similar size and OG.

By reasonable pitch, I mean anything from just a healthy vial (about half the correct pitch rate), to a huge starter with 2X the correct pitching rate. The higher the initial pitch, the less the yeast reproduce and vice-versa, so the end result will be a similar amount of yeast in the cake.

So if you are re-using the cake within a few days, just take a quarter of the cake and re-use. No starter, just pitch. This method works whether the original beer started with a clean beer, or one with lots of trub, and whether you wash your yeast or not. And there is no need for you to estimate how much of the slurry is actually yeast.

If you store the cake for a month, a lot of the yeast cells will have died. I usually estimate a 25% loss, meaning that if I store the cake (in fridge in sanitized Mason Jars), and re-use after a month, I up the pitch to about a third of the harvested cake.