There’s only one ingredient in beer that’s still alive when we put it to work. The hops have long been dried; the malt, kilned to death; the water never had a life at all. But yeast are still kicking when they arrive in a homebrewer’s hands. It takes a lot to keep them that way: sealed plastic packaging to keep out oxygen; storage at consistent, cool temperatures; and insulated shippers and cooling packs. In the right conditions, it’s not very difficult to extend the life of these microscopic fermentation powerhouses.

Reusing yeast is an easy process that takes place in four stages: harvesting, rinsing, storing, and pitching. In a small way, doing this makes homebrewing more sustainable by saving on cost per batch, getting the most out of the water used, and minimizing the amount of plastic packaging from yeast packets that homebrewing puts into landfills.

Which Yeast Strains Can Be Reused?

Tim Fothergill has a Ph.D. in microbiology that he puts to use as the head of packaging and quality at Denizens Brewing Co. in Silver Spring, Md. He has been homebrewing and reusing yeast for a decade with one yeast culture, which he started by mixing a pitch of British Ale and a pitch of Edinburgh Ale yeasts. He has rebrewed with this culture more than 40 times.

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Though his extensive use is possible, it is more common to reuse a single package of yeast somewhere between three and 10 times. Any yeast that has completed a successful fermentation can be harvested and reused. As long as the yeast doesn’t appear dark (a sign of oxidation) or give off unexpected sour or funky smells, it is ripe for repitching.

Luis Yanes, a homebrewer and sightseeing guide for the New York City tour company sarahfunky, says the yeast strain he repitched the most was Wyeast 1450. “It definitely got at least six uses,” he says.

When Candice Campbell, who has been homebrewing since 2012, began using more expensive liquid yeast strains from Omega Yeast Labs, she started to reuse her yeast. This can be a nice way to soften the increased investment when upgrading from cheaper dry yeast to more costly liquid yeast. With some yeast cultures priced at more than $12 per pitch, even getting three uses out of one package makes a big difference in cost — not to mention, saving on plastic packaging, insulated shippers, and, in warmer months, as many as three ice packs per yeast package.

Then, there’s the fact that 2020 happened: “My local homebrew shop was low on certain yeasts during the pandemic, so that was another reason to repitch,” Campbell says.

Campbell likes to brew saisons and wheat beers and has had success pitching American ale yeast, Kveik yeast, and German ale yeasts. Her gingerbread ale recently medaled at the second-ever homebrew competition she’s entered.

How to Harvest and Rinse Yeast for Repitching

Reusing yeast starts with getting yeast out of your fermenter after you’ve racked the beer into a keg or bottling bucket. It’s best to prepare for harvesting the night before, but at least four hours before you intend to rack the beer.

You’ll need a large pot for boiling, one 1-gallon heat resistant container (a glass carboy works for this), four 12- or 16-ounce heat-resistant glass containers with lids (Ball jars are perfect for this), and long tongs or another method for removing the glass containers from boiling water.

Boil the glass containers (one large, three to four smaller) in enough water to cover and fill them completely for about 30 minutes. Turn off the heat, remove the glass containers from the water, and place them on a clean surface.

Carefully fill each container with the boiled (now sanitized) water. Seal the containers and allow them to cool completely. You will need both the sanitized water and the sanitized containers for harvesting.

The rinsing step is sometimes referred to as “yeast washing” by homebrewers, though the term is more accurately used by professional brewers and refers to a process that uses chemicals to eliminate bacteria and potential contaminants from the culture. This process for homebrewers is far easier and can be referred to more accurately as yeast rinsing.

Fothergill’s team at Denizens Brewing conducts yeast washing in a lab. When it comes to treating homebrew yeast, he says, “I see this method as sedimentation steps.” That’s because the goal is simply to separate out the healthiest yeast cells from dead cells and trub particles around them — there’s no chemical washing happening.

  1. Rack the current beer off the yeast you will harvest. (This could be into a keg, bottling bucket, or other packaging container.)
  2. Once the beer has been racked into another container, pour the sterilized water from the sterilized 1-gallon container into the fermenter. Swish everything together and allow it to settle. (An advantage in this stage is that the water used to boil and sterilize the glass is the same water used for the yeast rinsing.)
  3. Once a layer of sediment has formed on the bottom of the fermenter (15 to 30 minutes, depending on the batch), carefully pour the top layer into the sterilized 1-gallon glass jar leaving as much of the settled-out sediment and trub behind as possible.
  4. Next, add the cool, sterilized water from the other glass containers on top of the yeast slurry in the 1-gallon container, and let this mixture settle. Be sure to put the lids back on the containers so the interiors remain sterile while waiting for the mixture in the larger container to settle. (Yanes speeds up this process by putting the mixture in the refrigerator, which accelerates sedimentation. Fothergill allows his mixture to settle while he goes about packing his homebrew, or cleaning, which takes about an hour.)
  5. Once the mixture in the 1-gallon container settles out, pour the very top quarter of the mixture off; it’s mostly water. (Another advantage in this stage is that the water used to boil and sterilize the glass is the same water used for the yeast rinsing.)
  6. Then pour the center of the mixture (Yanes describes this as “milky looking”) into the three or four smaller sterilized containers, filling them all the way to the top, and seal them. Leaving no extra space in the jar eliminates the potential for oxidation. Depending on batch size, you may only get three full glass containers, and that’s plenty of yeast!
  7. This yeast is now harvested, rinsed, and ready for storage.

How to Store and Repitch Harvested Yeast

Campbell simply stores her yeast in the sterile glass containers in the refrigerator until needed. “I even put some in small growlers with labels,” she says.

Yeast will need to do some waking up after their time in the cold refrigerator. Take a jar out at the beginning of brew day to give them some time to acclimate to room temperature before being pitched into fresh wort. Yanes usually sets out his jars at least three hours before pitching.

After yeast has come to room temperature (70 degrees Fahrenheit, give or take), give it a good swirl before pouring it into the fermenter over freshly brewed wort.

“Yeast rinsing is pretty easy. If you feel uncomfortable doing it, you can just pitch a beer onto the yeast cake,” says Campbell. This works best with yeast that was just used to ferment a relatively low-alcohol content beer, about 5.5 percent ABV or less. Fresh wort must be poured over the yeast cake immediately after the previous beer was racked off it to prevent contamination.

What to Expect from Repitched Yeast

Repitched yeast can have more vitality than the yeast that comes out of a manufacturing lab’s package. That’s because it has been beefed up on nutrients and fermentable sugars in beer and given the chance to multiply.

One thing to watch out for is the ABV of the final beer the yeast has just fermented — yeast will stay healthier and more vital if the ABV is increased after each successive pitch, not decreased. For example, fermenting a 5 percent ABV beer prepares yeast to ferment a 6.5 percent ABV beer, which gives them the vitality for an 8 percent ABV beer. The higher the alcohol in a beer, the most hostile the environment is to the yeast. For this reason, Campbell doesn’t recommend repitching anything that has fermented a beer over 8 percent. “I haven’t had success with it,” she says.

As generations of yeast (each reuse is considered a new “generation” of that pitch) increase, changes in behavior may occur. Both Campbell and Yanes noted a muting of yeast-derived flavors, like spicy phenols and fruit-forward esters, in later generations of yeast. “After the fifth time using Wyeast 1450, I noticed the fruity qualities in my NEIPA were not as pungent,” Yanes says.

However, Fothergill detected an unexpected increase in banana-like esters after about the 15th pitch of his strain. “After a couple of batches like that I went back to a previous generation,” he says. “Problem solved.”

Homebrewing is a hobby that requires an exorbitant amount of resources such as water to make the final product, so every drop that is able to be reused is important. This process makes the most out of water usage while recycling another pillar ingredient in beer — yeast. Now that’s an environmental win. Homebrewers may not store as many samples as a microbiologist like Fothergill, but if new flavors pop up in your own yeast culture, remember it is always possible to start over by purchasing a new pitch. After all, you already saved on cost and waste by repitching at all.