Washing the Unwashed: Reusing Yeast from a Primary Fermenter

“Brewers make wort. Yeast makes beer.” —Anonymous

A fermenting wort is in many ways like a living organism. Watch it carefully and you can see it metabolizing before your very eyes. Trub rises and falls inside the fermenter like an open circulatory system. A fermenting wort can increase in temperature by 4ºC or more over ambient temperatures. And most obviously, it respires, as evidenced by the rhythmic gurgling of a CO2 lock fixed to the mouth of an active fermenter.

Although a fermenting wort seems like it’s alive, it’s the yeast that makes it seem so. As every brewer knows, yeast is the magic in the carboy—the living component. As long as you’ve done your job as a brewer and provided your yeast a suitable habitat, it will do its job and repay your efforts in beer. You would be hard pressed to find a more rewarding mutualistic relationship with humans than the one we share with yeast. It just doesn’t seem fair that we should let our yeast die after fermenting only a single batch, especially when it has so much more life (and beer) to give.

In honour of my yeast’s hard work and dedicated service to my craft, I take it as my personal responsibility to extend its life as long as reasonably possible. By doing so, every batch of yeast started from a pure culture can be extended by approximately five times its single-generation life span. To extend my precious yeast’s life, I first wash it, give it a comfortable place to sleep, and then wake it up and feed it a yeast’s feast, for which I receive beer in return.

Washing Yeast

The first of two yeast washes

Layers forming after the first wash inside a carboy. The sludgy bottom layer is debris (to be discarded). The milky middle layer is basically active yeast, with a thin layer of beer on top.

After a yeast has worked tirelessly for a week or so in a primary fermenter, it’s tired and dirty and needs to be washed. Washing involves separating the active yeast from all the other debris in a primary fermenter, such as spent yeast, hops, trub, as well as miscellaneous proteins, fats, and other particulate matter. This separation can be accomplished in a few simple steps, always making sure to keep everything sterile so as not to contaminate the yeast.

Step 1: Separate the active yeast from the bulk of the remaining debris after racking. After you’ve racked your beer from the primary fermenter (I brew 19 L batches and these methods reflect my process; they can easily be scaled if you produce different sized batches than mine), add 4 L of temperature-matched and sterilized (i.e., boiled for about 15 min. and cooled to the fermenter’s temperature) water remaining at the bottom of the primary fermenter. Swirl the debris around to ensure that everything goes into suspension with the added water. It’s important that the water is temperature-matched with the fermenter to ensure that the yeast you’re trying to wash does not become damaged by a temperature shock. Cover the fermenter to prevent contamination, and let the slurry settle for approximately 15 min.

Step 2: Decant the active yeast fraction into a smaller vessel.

Layers after the second wash

The active yeast fraction from the primary fermenter can be decanted into a smaller vessel and again allowed to settle for about 15 min. This process further separates active yeast from undesirable debris. Notice the much reduced bottom debris layer and the proportionally larger active yeast layer.

After the slurry has had a chance to settle, you’ll notice that it has clearly separated into a thick bottom layer of debris (to be discarded), a cloudy layer of active yeast in suspension, and possibly a thin layer of beer left over from the rack (which can be safely ignored). Carefully decant the upper layer of active yeast into a sterilized 4 L container while leaving the debris behind. I prefer a clear glass container for this so that I can see when the various fractions have separated. Cover the container to prevent contamination, and let it stand for an additional 15 min. so that separation can once again occur.

Step 3: Decant the active yeast fraction into smaller containers for long-term storage. This is the second washing step. As in Step 2, decant the upper active yeast fraction into sterilized 1 L containers. I use mason jars for this step so that I can put sterilized lids on the containers for long-term storage. Seal and store.

Step 4: Refrigerate the yeast for long-term storage. Refrigeration will cause the active yeast to enter a state of temporary dormancy which will allow it to be stored for an extended period.

Settled yeast after 24 h of refrigeration

The washed yeast enters a state of temporary dormancy after 24 h of refrigeration.

You should be able to get away with several weeks to months; although, some have reported successfully storing yeast this way for a year or more. Your mileage may vary. In order to revive the yeast, simply remove it from the refrigerator and allow it to slowly come to room temperature. Once there, swirl the dormant yeast into suspension and start building a starter, as per your normal practice.

When to Let Yeast Die

Death is an essential part of life. Sometimes it’s in a brewer’s best interest to know when to let their favourite yeast die. The first time you pitched that yeast, it was likely from a pure culture. It was young and vibrant. However, with each successive generation, a yeast’s character can change. It can become sluggish, produce off flavours, and develop a generally bad attitude. Several factors can cause these changes, from subtle genetic mutations that accumulate from successive culturing, to the introduction of wild strains of unwanted bacteria or yeast, among others. If you’re careful, you can expect to get four or five generations from a pure yeast start—but, for most, five generations is probably the top-end. If you start to notice odd flavours creeping into the beer you ferment from a recultured yeast, it might be time to retire the line. Most importantly, rely on your senses. If you open a culture jar and notice off odours, don’t use it.

Washing yeast and reusing it is a great way to stretch your yeast dollar and cut down your cost per batch. But don’t wash yeast for the financial benefit; wash yeast to honour another living being who works harder than anyone or any thing with the unitary purpose to bring you beer.

Honour thy yeast.

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About The Happy Homebrewer

In relentless pursuit of the perfect pint.
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7 Responses to Washing the Unwashed: Reusing Yeast from a Primary Fermenter

  1. phirx says:

    Thanks for this thoughtful and detailed article. I am looking forward to trying this. When you decant the yeast in steps 2 & 3, do you use a siphon or simply pour it off, leaving the trub behind? Thanks, phirx

    • I just simply poured the yeast fraction off the trub. It’s quite a bit easier than it sounds. As long as you’re using clear glass containers, you can see when you’re getting close to pouring off the trub.

  2. phirx says:

    I use a plastic bucket fitted with a lid for primary – would a feasible process be to add the sterilized water to the primary fermenter after racking the beer, then stir it up and pour or siphon into a smaller glass container before letting it settle and step 2?

  3. bagboilbeer says:

    Great post, thanks. Really clear and useful. You make it sound so easy… must give it a try sometime. Cheers!

  4. Skully says:

    I’ve used this rinsing method with great success, but since I always make a starter anyways, I think I’m going to switch to this method: http://brulosophy.com/yeast-harvesting/

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