Using a yeast cake

Edit: I do not advocate this method anymore. I do advocate re-using your yeast, but you should wash it first.

If you brew regularly, and especially if you like to use liquid yeast strains, you might want to consider reusing your yeast. As with everything in homebrewing, there is a long list of do’s and do-not’s, but in general, it’s pretty easy to decide if repitching on yeast will work for you.


happy-yeast

First of all, if you don’t use liquid yeast, the only reason to re-pitch onto your yeast cake is if you’re brewing something big, like an imperial stout or barleywine. Something with a gravity over 1.080. The reason it is helpful in this case is that you have a large, recently active yeast colony, ready to go to work. Of course, you could just buy 2 packets of dry yeast, but why not use what you already have? It’s worth a shot to see how it works. After all, isn’t that why we homebrew in the first place?

Ok, so you use liquid yeast, not dry. That’s typically $8 a pop, give or take a couple bucks. That’s a big chunk of your supplies, and if you can stretch it over 3 batches, it’s suddenly no more expensive than dry yeast. In fact, many brewers will re-use yeast up to 10 batches.

So you’re in. You want to re-use your yeast. Now again, there are choices to make.

The easiest way to go is to rack off your finished beer from a previous batch, either into your bottling bucket, or into a keg. You leave behind the trub and yeast. Yum. Do this the same day, or the night before you’re going to brew. Re-cap the carboy or bucket just as if there was beer in it, and store it in a relatively cool place.

Make your wort, and after cooling down, instead of racking (or funneling) into an empty carboy/bucket, put it into your carboy with the yeast slurry left from your previous batch. Shake well (aerate), and prepare for some serious fermentation. If you have a blow off tube, you might want to keep it handy, especially if this fresh batch is a high gravity brew.

So what things are there to look out for?

First of all, some of the hop flavor from your previous batch will be in that yeast cake. Don’t do an IPA in the first batch, then a mild or wheat in the second round where you wouldn’t want that hop character (potentially) bleeding over.

Second, don’t reuse yeast if your first batch was a high gravity batch. The rule of thumb is not to reuse yeast if your batch was over 1.060. The only reasonable explanation I’ve heard about why this is, is that the alcohol in that high gravity fermentation will weaken the cell walls of the yeast and cause them to produce some undesirable flavors.

Third and last (for this article anyway), is a violent fermentation. Prepare for blowoff, and also for a hot fermentation. You may want to have an ice bath, or temperature controlled fermentation environment to avoid too hot a fermentation.

That’s it. Have fun with your yeasties!

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6 thoughts on “Using a yeast cake

  1. Doug

    I just used this method but fermentation seemed to proceed at a normal rate. The new wort went on the yeast cake about 11 or 12 days after the first batch started fermenting. In hindsight, I didn’t aerate the new wort vigorously for fear of washing all the junk from the first krausen into the new brew. I’ll check the gravity when I dry hop it.

    Due to the limitations of volume in my secondary carboy, some of the fermented beer from the first batch had to stay and be mixed with the wort. We’ll see how it turns out.

    Reply
    1. Joel Mahaffey

      How much yeast was there at the bottom when you pitched? If you didn’t mix up the yeast cake well, you may not have released much of the yeast into solution.

      I know there was probably a lot of hop trub in there, which would have re-settled back out anyway. Ideally, there woudn’t be that much trub to get in the way of the yeast, but homebrewing is usually not the ideal scenerio.

      Given how much trub you had in there the first time, and definitely after the second batch, I wouldn’t re-use the yeast cake, just due to concerns about infection from all the other sludge in there.

      Check this out for a good method to clean your yeast, and get it back to a more or less clean product:
      Yeast washing

      Reply
  2. Doug

    Ok, so I just bottled the first batch of beer. That one fermented from a fresh liquid yeast starter and had I.G. 1.060. It came out of the secondary at 1.014 after about 21 days total. The batch I put on the yeast cake (the one I mention above) also started out at 1.060. It fermented for 10 days and just went into secondary at 1.010. So… I won’t worry.

    Thanks for the yeast washing article. It looks like something I will try this summer.

    Reply
  3. Raymond

    I just listened to the Brewing Network. They discussed how to wash the yeast off the trub. Pretty cool.

    Raymond
    Seacoast Homebrew Club (Just starting in Portsmouth NH)

    Reply
    1. Joel Mahaffey

      Yes, you’re really better off washing your yeast. I’ve pitched directly onto the cake a number of times with little to no side effects, though it’s not a best practice for sure. Check out Jamil & Chris White’s new book on Yeast. It’s excellent.

      Reply

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