So you’ve brewed your beer, and it’s fermented in primary for a week. You’ve racked it on over to secondary and stashed that bad boy someplace cool and dark. Now it’s time to clean up. You look down into your primary and see all that goop in the bottom. Throw it out? No way! That’s a lot of viable yeast down there, and I’m going to show you how to use it again in your next batch (and maybe the next, and the next…).  

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The easiest way to re-use your yeast would be to just dump a new batch of wort on top of the trub (a.k.a.yeast cake) and let it go to work. No problem at all with that method; you just have to brew and rack on the same day. It’s not that big a deal to rack one beer while you’re cooling down another. If you do it this way, just remember to go from lighter to darker (both in color and in alcohol content of your beer). And you probably will want to use a blow-off tube. Fermentation is pretty fast and furious this way.

There’s another way of re-using the yeast, though, that doesn’t require you to have a new batch ready to go. It’s called yeast washing, and it’s pretty easy too. For this job, you’ll need some things. First off, you’ll need the yeast cake from a batch of beer.

Secondly, you’ll need a few jars. I happen to have Ball/ Mason style canning jars around my house, so I just use those. You’re not putting pressure on them, though, so they don’t really have to be ‘canning’ jars. They just have to be sanitized thoroughly and not have cracks running through them. 


Notice mine have aluminum foil hats on in the picture. That’s because I’ve already sanitized them. Aluminum foil is like the home brewer’s duct tape. It’s got a million and one uses, and one of ’em is to keep bacteria and other beasties that like beer out of yours (most of those beasties are airborne, meaning they travel on air currents and fall into your beer). Plus, the foil is oxygen permeable, so it allows any co2 buildup to escape. 

So your equipment is ready. Swish your primary around, get everything in there good and mixed up. Now take your jar (quart-sized, if you have it; if not, 2 pints will get the job done as well, though you’ll need at least 4 total) and carefully pour the yeast cake into it. Depending on how much trub there is, it probably won’t all fit into your jar. That’s ok; you don’t need it all, but if you want to get crazy, just increase your jar collection and get everything you can next time.

Re-foil your jar. It should look like this: 

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Stick it in your fridge, and get busy cleaning up your primary and racking equipment. Make sure to take everything apart to clean it, and drip-dry those hoses; don’t give the bugs a chance to contaminate your gear.

After about an hour, look in on your yeast. It should have started to separate as the trub gently sinks to the bottom, leaving the yeast suspended in beer at the top. Now’s when the next jar comes in. GENTLY pour off the top liquid into your second sanitized jar. Put the foil back on top of it.

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You’ll probably wind up with some of the trub in this jar, too. Don’t worry about it. You’re going to repeat that last step, anyway, so get this sucker into the ‘fridge. Give it 30-45 minutes, then check it again.

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Here we have very clear separation. The trub has settled to the bottom again, the lighter stripe in the middle is yeast in suspension, and the darker band at the top is the beer. Again, you’re going to pour this off into another (or the first, if you only have two) sanitized jar. Follow the process one more time, and stick it into the ‘fridge. 

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After another hour or so, about the amount of time it took to type out this article. Separation is very well defined. You can see the yeast beginning to settle out on the bottom of the jar. This will continue until all of it has settled, and you’ll have a nice protective layer of beer over everything.

You can leave it in your fridge as-is (covered in foil), though if you do that I’d recommend using it within a few weeks. A handy trick I’ve learned, though, is to sanitize an empty beer bottle, and using a sanitized funnel, pour the yeast into it. Cap it like you would a beer, and store that in your fridge. The brown bottle will protect it from any harmful light rays, and the cold will force the yeast into hibernation. When it’s time to brew again, remove the bottle to room temperature for a day, then pitch it into a yeast starter a day before brewing to wake everything back up. Pitch it as you normally would.

You can repeat this process as much as you like, though the prevailing wisdom in the homebrewing community is that 3 generations of yeast is probably as far as you want to push it. After that, genetic mutations within the yeast can begin to change the flavor profile.