The most expensive/annoying/scary things about brewing, yeast.
Sometimes I go months between brewing (not usually), and sometimes I have been known to “stock up” on yeast (I’m an idiot). When ordering ingredients I often try to predict what beers I will be brewing in the foreseeable future and thus what yeast I will need and order them all at once to save on shipping. 6 months later, a couple days before brew day, when I dig up the yeast and see it is well past expiration, I am forced to either roll the dice and hope it is still viable, or head out to my local home brew shop (LHBS) and hope they have whatever crazy yeast I purchased previously in stock, spoiler alert, they usually don’t.
Freeze your yeast.
Freeze your liquid yeast? Yessir. Freezing yeast allows you to maintain a bank of your favourite yeasts, available at your disposal whenever you decide to brew. In general when preparing for a brew, you make a yeast starter, now instead of doing so with a liquid yeast pack, you can do so with a frozen vial from your yeast bank.
Not only is yeast banking an excellent way of maintaining a supply of your favourite yeast strains, but it is also super economical. In practice I think I have managed to split a single vial something like 16 ways.
How do you go about freezing yeast? I essentially copy the methods laid out here. Effectively you make a starter to bump up the yeast population/make sure it is viable to start out with, decant off as much of the beer produced during the starter process, add some glycerin, pop in the freezer, and done.
I recommend you do this with a couple of your brew buddies, and you pick different strains, otherwise you might end up with 15 vials of yeast that you may only brew once a year with, spread the wealth!
Required Materials
I’m going to outline the ideal set of materials here, you can probably get by with less than this.
- Glycerin
- Purchased from drug store.
- Graduated cylinder (100mL)
- Used for measuring out glycerin solution as well as for measuring amount of yeast slurry.
- Erlenmeyer flask(s)
- To make starter in, I also use a small Erlenmeyer to prepare my glycerin solution, but this is not necessary.
- Conical bottom centrifuge tubes (15mL)
- To store yeast
- Isopropyl (Rubbing) Alcohol
- Optional but recommended
- Mason Jars
- For freezing yeast vials suspended in isopropyl.
Method
- Make a starter and wait for fermentation to complete.
- Usually takes a few days, once fermentation has ceased, you want the yeast to settle out of solution as much as possible, I sometimes put my starter in the fridge to get the yeast out of solution.
- Make a 25% v/v solution of glycerin in water.
- I usually make about 100mL so which equates to 25mL of glycerin and 75mL water.
- Sterilize your solution.
- If you have a pressure cooked and can pressure cook for 10 mins, that’s great, otherwise just boil the crap out of it. This will boil off water which has a much lower boiling point than glycerin, so you may want to add slightly more water when you start to keep the ratio approximately 25% v/v glycerin.
- Collect 100mL of starter.
- In the process of decanting your starter, try to make sure there is just enough liquid left so that you can swirl the remaining yeast cake to the point where you are able to pour it out into some sort of measuring device, I use a graduated cylinder.
- Combine starter and glycerin solution and portion.
- Obviously chill down your sterilized glycerin solution so you don’t cook the yeast you just propagated, and combine 1:1 your yeast slurry and your glycerin solution. This should have you end up with approximately a 12.5% v/v solution of glycerin which should be sufficient to prevent the formation of ice crystals in the majority of your yeast cells, which cause them rupture during freezing.
- Portion the solution off into tubes that you have sterilized, I use something like this to store my yeast. If that link dies for some reason, just look for 15mL conical bottom centrifuge tubes on amazon.
- Freeze.
- Once all your vials are filled, cap them all, and give them a shake to ensure the glycerin/yeast are good and mixed. If possible place the tubes into a container containing isopropyl alcohol (rubbing alcohol) and place in a deep freeze. If you don’t have rubbing alcohol you can just place the vials directly in the freezer, but the alcohol works to reduce the freezing rate in the cells which increases their viability. I usually fill a mason jar with vials and top up with isopropyl, then put this whole thing in the freezer. The isopropyl can be re-used over and over again.
- Ideally all this freezing should be done in a deep freezer, not a “frost-free” freezer which can go through thawing cycles and shorten the lifespan of your yeast.
- Make starter with frozen yeast.
- Give yourself and extra day or two lead time before brew day to get the yeast going, but other than that you can use your frozen vials just like you would a liquid starter.