Yeast Harvesting

If you’ve been brewing for a while you’ve probably noticed how quickly the price of yeast stacks up. At my local homebrew shop, a smack-pack of WYeast is about $9, and a fresh packet of dry yeast is $4.50. I brew about twice a month and almost always use liquid yeast, so that’s almost $20 a month in yeast alone. If I didn’t make starters, it would be somewhere in the $80 a month range to hit the proper cell counts. On top of this, I collect yeast like some people collect stamps, and I love culturing yeast from bottles that may not be commercially available. To alleviate the costs of yeast, and to gather some unique strains, many brewers begin harvesting their yeast.

What is yeast harvesting?

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Yeast harvesting is the practice of culturing yeast from a previous batch, yeast pack, or bottle with the intention of building up the cell count and pitching it again. This can be done for a variety of reasons, a few of which I’ve mentioned.

Yeast harvesting is the practice of culturing yeast from a previous batch, yeast pack, or bottle with the intention of building up the cell count and pitching it again. This can be done for a variety of reasons, a few of which I’ve mentioned.

Some Pros

First off, yeast can get pricey. Most standard ale pitching rates (.75 million cells per mL per degree plato) would recommend almost 200 billion cells of yeast for a 5 gallon, 1.055 OG batch. That’s two fresh smack packs, pretty pricey. By harvesting yeast, you can continue making starters and building up to your cell count, so you’ll only be buying the ingredients to make your starter wort.

Second, if, like me, you like trying unique yeasts that aren’t commercially available, you can harvest yeast from unfiltered bottles. For a long time, this was how most people got a hold of the Conan yeast from Heady Topper. It’s also how people gets the Bell’s house yeast, since Oberon is low gravity and unfiltered.

Third, not all yeast is easy to find. Even if it is commercially available, it may be a seasonal strain or one that is often sold out. You may also not want to spend money on shipping, and your LHBS is out of the way.

Some Cons

When you’re harvesting yeast, you may run into a few problems that can be detrimental to your beer.

Right off the bat, there’s the increased chance of infection. If you harvest yeast from the slurry of a previous batch and something found its way into the batch, your basically combining those strains and making a starter out of them, then pitching them into a new batch. This could, at worst, ruin a batch and possibly fermenter, and at best, might hurt the quality of your finished beer.

Yeast also changes mutates over time. High gravity batches have more osmotic pressure and can impair yeast health and viability. If cells begin to deviate from their original strain and you continue to harvest and build more generations, those mutations can continue to grow and flourish in the sample. In other words, there is no quality control.

Storage can also be tough. Some people recommend glycol solutions for storing yeast, I personally store with sanitized water. I also use 50mL centrifuge tubes to store yeast, and I know people who use mason jars. Either way, storage takes space and needs to be done properly.

So how do I harvest yeast?

Good question, and you have a few options, mainly they have to do with what your goal is.

Harvest from a slurry

thumb2_img_0256-18766Your first option is to harvest the yeast from your slurry, the sludge at the bottom of your fermenter after your batch has been packaged. To do this, you’ll need to do what is called yeast washing:

  1. Package your beer
  2. Scoop some of the remaining slurry into a sanitized jar/cup, preferably one that you can see through.
  3. Boil some water (to sanitize it) and let it cool. Pour it into the cup and mix the solution.
  4. The solution will begin to settle, and you’ll begin to notice a darker layer at the bottom than the top. This is the trub, hop and protein matter that are heavier than the yeast cells. Let the solution settle for about twenty minutes.
  5. Sanitize another jar/cup and decant the top layer of yeast and liquid into the jar, leaving behind the layer of trub. You can now either repeat this process to get more trub out of the solution, or package the mixture.

There are people who also think that the washing step is entirely unnecessary, instead either estimating their cell count and pitching the correct amount from the slurry, making a starter out of the “dirty” (with trub) slurry, or even racking onto the old yeast cake. How you do it is up to you, I’m partial to yeast washing.

Harvest from the starter

This method, popularized by the fantastic blog Brulosophy, involves making a starter of liquid yeast to hit your intended cell count, and then taking some of the yeast from the starter to build from again at a later date. This is the method I use, it has the perk of not needing to be washed and the yeast doesn’t suffer from the effects (time, environment, osmotic pressure, etc.) of fermentation. You can use a yeast starter calculator like the one at BrewUnited and set an “overbuild” count, or, more cells than you need so you can harvest from the starter and still hit your intended cell count for the batch.

  1. Define how many cells you’ll need, and make sure you use a larger starter than necessary to “overbuild” the cell count.
  2. Make your starter, harvest in a sanitized vessel, then pitch the remaining yeast into your beer.
  3. Package, store, repeat.

It’s a pretty simple process, but make sure you keep a log of what yeast is stored and when it was stored. I’m skeptical of yeast viability numbers in general, but there is no doubt that they are less viable over time. So, if necessary, make a small starter every now and then to keep the vial viable. If it’s been over six months, make a very small, low OG starter first to bring the culture back up.

Harvest from the bottle

Have a bottle of Oberon you want to harvest from? Friend hand you a homebrew and you want to save the yeast? This is the method for you.

  1. Find an unfiltered beer. It needs to be unfiltered so that the yeast hasn’t been filtered out.
  2. Let the bottle sit in the fridge for a few days so that the yeast can settle to the bottom of the bottle.
  3. Open the beer and sanitize the lip of the bottle/can with a flame. Don’t want any bugs along with the yeast.
  4. Pour the beer and leave about ¼ of the beer still in the bottle or can. Be careful to pour in one motion so the liquid doesn’t kick the yeast back into suspension.
  5. Make a starter. Start small and low gravity, we will slowly work our way up. Here are the steps I use:
    1. First starter: 150 ml of 1.015 OG wort
    2. Second Starter: 300 ml of 1.020 OG wort
    3. Third Starter: 450 ml of 1.030 OG wort
  6. Now that you have your starter, package and store!

As always, keep viability in mind. If the bottle is incredibly old, give each of these steps a little more time and maybe even consider repeating step one or two.

Storing yeast

IMG_20151229_175545221Yeast storage has been pretty debated, primarily in arguments of viability. Some people swear by glycol, or preparing slants. Personally, I follow this method and have never had any problems:

  1. Make sure you are storing your yeast in cold temperatures, the ideal temperature range is about 33˚F-38˚F. Never let the yeast freeze, try to keep it as cold as possible. I’d aim for 34˚F.
  2. You can either store it with boiled water (let the water cool first), or store it with the wort from the starter. Meaning, if you’re storing from the slurry or the starter, just pour the full volume into your storage vessel and seal, without leaving room for air.
  3. Store it in a sterile container. I personally use plastic centrifuge tubes. Plastic is typically more resistant to the pressure, which is useful in case the Co2 builds up.
  4. Store it with as little oxygen as possible.
  5. In storage, yeast can still produce Co2 for a while since most refrigerators aren't cold enough to stop the yeast immediately (and you wouldn't want it to be that cold in this case). For this reason, you want to release Co2 from the container every now and then for the first day or so.

Culturing yeast isn’t difficult at all, and can be a huge step towards saving money in your brewing! Once you get culturing and storing down, you can even look into capturing wild yeast from fruits! It’s a skill to put in your brewer’s belt, happy homebrewing!

written by Matt

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9 comments on “Yeast Harvesting”

  • I have a pale ale fermenting now using yeast I washed from a previous batch as an experiment to see how it goes. Hoping it turns out well as this was my first ever attempt at washing and saving my yeast from a previous batch. If it turns out well I will definitely be using this method more in the future.
    Great article and tips thank you.

  • Once cultured how long can you store yeast in refrigerator without negative affects.
    At what point should you dispose of it or when do you know if it has gone bad?

  • Nice article, very informative

  • Hi,

    Thanks for this guide
    I wonder about your timing. I guess you give the harvested yeast some time to come up. So brewing days should be some days after reactivation day.
    How do you set up the Starters? Simple sugar wort?

    • David Doucette

      Correct, you want to give a few days to step the yeast back up to a good cell count. Make the starters out of Dry malt extract.

  • Having never attempted harvesting from slurry, is there more detailed info available concerning water measurements, estimating yeast counts from the slurry, how much to use in your next batch, ectera?

  • Yeast count? nonsense, I just put some schmeg from the bottom of the primary ferment-er in a sm. mason jar, about 1/2 full, and leave the lid loose. I store it in the fridge no longer than 6 weeks. Brew day, I remove it, bring to room temp,add 1 tsp. of sugar and it's ready to pitch by the time wort is cooled.

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