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