Mash Out!—How to harvest yeast?

In this edition of Mash Out!, we’re going to talk about harvesting yeast. Much like many aspects of home brewing, this is something that you can do quite simply or it can become a much more involved, scientific process.

First things first: No matter what technique or equipment you’re using, if you do not use proper sanitation practice, you’re wasting your time and money.

Here’s what you’re gonna need:

  • a fermenter with a yeast cake from a freshly transferred beer
  • sanitizer like StarSan
  • 2  x one gallon jars with lids
  • 4 smaller mason jars with lids
  • a one gallon pot
  • water
  • lots of ice or an immersion chiller
  • plastic wrap

We’re going to assume that you’re using fairly entry level equipment such as a carboy.

With proper sanitation practice under your belt, we can get started with a finished batch of beer. After you’ve cold crashed your beer and transferred to a keg or bottled it, spray a piece of plastic wrap or tin foil with your preferred sanitizer (I use StarSan) and cover up the mouth of your carboy.

Set your covered carboy aside, and put a gallon of water on the stove in the one gallon pot. Crank it. While you’re waiting for the water to heat up, sanitize your one gallon jars, their lids, your mason jars and their lids. I have read articles that recommend boiling these, and it certainly works, but I’ve found using StarSan to be just as effective with less risk of scalding yourself.

Bring the water to a boil and put your immersion chiller in it (assuming you’re using one). Let the water boil for ten minutes and then transfer to an ice bath, if you’re not using a chiller, or start running water through your chiller. 

Once your water is cool (65°F), remove the covering from your fermenter, spray the mouth of the fermenter and using the sanitized funnel, pour the cooled water into the fermenter. Agitate the water and yeast cake around the fermenter until it is well mixed then pour the contents into a 1 gallon jar. Place a lid on the jar of yeast cake and water and shake the heck out of it. Set the jar down and wait 10 minutes.

As the jar sits, you’ll notice the liquid separating into three layers. After 10 minutes, take the lid off the jar and pour the top layer (which is mostly made up of water) down the drain. 

Now, carefully pour the second layer into the other one gallon jar. Leave behind as much of the third layer as you can. 

After pouring off the second layer of liquid into the second jar, place the lid back on and give it another really good shake. Let the jar rest for 10 minutes, pour off the top layer and then pour the second layer evenly into the four smaller jars and seal them up. 

It’s a good idea to label the jars with the yeast strain, the date and the generation of yeast.

Place the yeast in a fridge and save it for another brew day. 

It is recommended to use the harvested yeast within 3 months and with a starter.

If you have any questions that you’d like to see in Mash Out, send me an email at See you next month!

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