Tuesday, October 22, 2013

Washing and Freezing Yeast with Glycerin in a Frost-Free Freezer

In this post I'm detailing a method I have used to wash and freeze yeast from a slurry, including how I made my glycerin mixture. I did this ONCE at the time I wrote this post, so I am new to this stuff. Yes, this has been done before by others, and I provide links to a few sites where I got my info. This post is meant to track the method I am using.

A big ol' healthy starter. This is what
we're after! 
First off - a warning... This is a new process for me, and I'm still learning all the "best practices." I culled my method from a few sources--most notably a friend on the Albany Brew Crafters homebrew forums who has been banking yeast for awhile now, the washing and freezing yeast page on swedhelm.net, and this great how-to write up on Homebrewtalk. Seriously, check out these resources -- they go into more of the "why" behind this process. Also, I'm doing this for temporary storage purposes of some of the strains that , and don't have a giant lab or complex equipment (beyond that of a geeky brewer). I work under sanitary conditions, not sterile conditions. Some will scoff at this, but I'm going for simplicity here, and don't want to dedicate too much time or money to this endeavor. I use star-san because that's what I have. I don't own a pressure cooker or a microwave (its ok to laugh...), so I use my stovetop and electric teakettle.  I am not a scientist, nor do I play one on the internet!!

Washing and freezing yeast for future use is a practice that has multiple benefits in the ambitious homebrewery. First off, it'll save you money. You need yeast everytime you make beer; while a pitch of readily available (White Labs or Wyeast) yeast typically cost between $7 and $9, you can stretch this across numerous brews, drastically decreasing the cost of each batch. Secondly, it allows you to collect and "bank" all those hard-to-find or seasonal yeasts for future uses or trading. Sure, I brew saisons year round, but I do like to switch up my yeasts here and there, depending on the size and interpretation of the beer, and whether or not I want to add Brettanomyces after primary, for example. If I bank a few strains of saison yeasts (such as Bootleg Biology's Funky Saison), I have those on hand whenever I feel the itch to brew. Finally, harvesting yeast just feels like part of brewing. I would argue it makes you pay closer attention to yeast health and pitching rates.

Because I'm writing this as much for me as I am for you (that happens a lot on this blog, if you haven't noticed...), I'm just going to run through the equipment I used and my basic process. I'll see how this pans out this first time and maybe modify this post in the future. (Maybe.)

One tea candle
Yeast slurry with beer on it (in a mason jar)
Glyerin (I used "Now" brand)
50 ml tubes with lids
2000 ml Erlenmeyer flask
250 ml Erlenmeyer flask
One 2-liter soda bottle with lid, sanitized (for storing glycerin solution)
Additional mason jars (for washing yeast)
Star-san in a spray-bottle
800 mls boiling water
~1 Liter of boiled and cooled water for yeast rinsing

So many household applications...
Step One: Make 20% Glycerin solution.
People smarter than me ran some super smarty-pants science tests, and figured out the ideal percentage of glycerin for freezing yeast in a frost-free freezer is between 10 - 15%. (This is from the Homebrewtalk how-to.) If you mix a 5:1 water:glycerin solution with the same volume of yeast slurry, you hit your 10% glycerin content. I wanted to make a liter of the 20% solution so I have it on hand whenever I want to freeze some yeast. This was super easy in metric -- 800 mls water plus 200 mls glycerin.

I also wanted to store this sanitarily, so I could just pour and go at later dates. I don't have an autoclave or pressure cooker, or I would have gone that route. Instead, I simply heated 800 mls of water in an Erlenmeyer flask, and added the 200 mls of glycerin once it was boiling. After it returned to a boil, I turned off the burner and let it sit there to cool down. It took a couple hours to chill, but it held over 180 for about a half hour or so. This in my mind was good enough, and really it was like 5 minutes of hands-on, so the time investment was right.

Step Two: Rinse Yeast.
Before freezing, you want to get some good clean yeast. I'm working from a couple of yeast cakes I stored in mason jars, and they have a bunch of trub mixed in with the yeast, so I need to "rinse" the yeast. This is pretty easy:

(0. Its best to do these steps next to a candle or a flame of some sort -- this keeps any airborne bugs from landing in your samples.)
1. Put your harvested cake in the fridge and let the yeast settle until the jar "clears." This could take a few days to a week, depending on the flocculation properties of the yeast strain.
2. Decant the beer off the top of the cake.
3. Add some of the boiled and cooled water to the mason jar. Add about the same volume as the remaining cake.
4. Mix it up really well and return it to the fridge.
5. Wait anywhere from 5 minutes to a half hour, depending on the strain and flocculation properties. You'll notice the water will still be cloudy, and the darker matter (trub) will have settled to the bottom of the jar.
6. Decant the water and a bit of the creamy top layer into another sanitized mason jar. Repeat this a few times if desired to get all the good stuff. (Don't forget to label the jar, especially if you are working with multiple samples.)

Step Three: Concentrating the Yeast Sample.

After you've separated the healthy yeast from the trub, the next step is to get an acceptable
concentration of yeast in each of your vials. You want to combine a dense slurry with the glycerin solution, so when you thaw it out it'll be ready to rock without too much stepping up. The mantra here is "shake, wait, decant, repeat."

First, shake the mason jar with your rinsed yeast. Let it settle for ~ 5 minutes in the fridge, and pour the cloudy liquid into your vials.

Then, return your vials to the fridge and wait for them settle for about a half hour to 45 minutes.

Then decant the liquid from each of the vials, retaining the slurry at the bottom.

Repeat this process until the slurry fills about 2/5ths of the vial. On my 50 ml vials this is about 20mls of slurry.
This is about 1/5th of the vial.
You can also see my coozie in the background,
holding my samples upright (see step five).

Step Four: Add the Glycerin Solution.
This ain't rocket science, but remember to add the same amount of the 20% glycerin solution as you have slurry. This should leave about 1/5th of the vial for expansion during freezing. In my 50ml vials, this is 20mls of solution. Shake it up really good to mix the glycerin solution with the slurry.

A few frozen vials with my insulated
lunchsack and beer coozie.
Step Five: Insulate and Freeze.
In order to shed moisture, a frost-free freezer actually goes through occasional defrost cycles. The constant freezing and thawing of yeast could damage cells, so homebrewers typically insulate their yeast collections in some fashion. You also want your samples to freeze upright. Thinking about this stuff, I bought an insulated lunch bag, and packed it with an icepack and a beer coozie. Simple, cheap and effective. Of course, I'll need to come up with a more commodious solution as my library grows, but in the interim this works great.

UPDATE 2/18/2014: I successfully thawed out some of the Bootleg Bio yeast that I froze, so this method works!!


  1. For a non scientist you sure got a killer stir plate and some sweet glass ware!

    1. I found some great deals on glassware on Amazon -- a set of 5 pyrex Karter-Scientific Erlenmeyer flasks for ~$20. The Corning stirplate was a fortunate score, but my other one I build with a computer fan and hard drive magnets.

      After seven years of brewing I've accumulated a lot of stuff. One of these days I need to get rid of some of it, certainly...