How to freeze yeast (INTENTIONALLY)

Why freeze yeast? ► Slows down biological activity keeping it viable, potentially for years ► Cost savings over buying fresh yeast for every brew ► Build up a yeast bank of different varieties, especially rare/hard to find types or types not often used by yourself ► Reduced generational mutation over time ► Less storage space needed ► Potentially lower chance of nasties getting a hold ► If you already make yeast starters, then the process is super simple

Needed Equipment ► Screw cap test tubes, sterile, freezable (autoclavable optional) ~£15 pack 50 ► Test tube rack ~£6 ► Vegetable Glycerine EP/USP grade ~£10/L ► 10ml oral syringe, sterile ~£7 pack 10 ► Isopropyl alcohol 99.9% ~£4/L ► Sanitiser and hand gel (we already have some of that right!) ► A pressure cooker ► If you are already making yeast starters, easily less than £50* to be able to start freezing yeast ► Each filled test tube costs around £0.50p to make

What is vegetable glycerine Vegetable glycerine, also known as glycerol or glycerin, is a clear, odorless, and sweet-tasting liquid that is derived from plant oils, such as coconut, soy, or palm oil Common Uses: • Sweetener or humectant, common in baked goods, candies, and soft drinks. Acts as a solvent for flavours and food colourings. • Used as a moisturizer in lotions, ointments, creams, soaps, and shampoos • Found in cough syrups, elixirs, and capsules as a solvent or lubricant. • E-liquids for Vaping • Sometimes used as a base for herbal tinctures and extracts. • Glycerine is often added to products to extend their shelf life due to its moisture-retaining and stabilizing properties. Vegetable glycerine is considered safe for use in food, cosmetics, and pharmaceuticals. It’s generally non-toxic, hypoallergenic, and non-carcinogenic. However, ingesting large quantities may cause digestive issues because of its laxative effect.

Why is it useful for freezing yeast ► Freezing Point Depression ► Has lower freezing point than water so when mixed with water, it helps to lower the freezing point of the solution significantly ► Cryoprotectant Properties ► Glycerine acts as a cryoprotectant, meaning it helps protect biological tissues or cells from damage during freezing by preventing ice crystals from forming. This property is used in medical and biological applications, such as freezing blood cells, or tissues for storage ► By disrupting the formation of ice, glycerine prevents sharp ice crystals that can damage cellular structures.

High Level Process Prepare a Glycerine Mix Create a yeast starter Package yeast into test tubes Freeze Defrost, build a starter & pitch

1. Prepare a vegetable glycerine mix ► Process ► 75ml Glycerine (or 94.5g by weight) ► 225ml water (I use distilled/RO) ► can basically make any batch size, just keep ratio of 25:75 glycerine:water ► Place into a pressure cooker, bring up to max pressure and hold for about 10-15mins then turn off heat and let cool naturally ► Reasons for “autoclaving” are: ► Sterilize, or as close to as we can get on a budget. The heat and pressure should kill pretty much everything nasty ► Helps preserve the solution integrity

2. Create a yeast starter ► Take our nice fresh packet of yeast for our brew and build a starter as normal ► However, we are going to overbuild it by 200ml ► Before the yeast has started to settle out decant 200ml into a sanitised kilner jar ► Put this 200ml jar to one side to let finish fermenting the starter out and cold crash when it is finished

3.1 Package the yeast (before-hand) ► Prior to packaging the yeast, put some of the isopropyl alcohol into a little tub and put into the freezer. You’ll want enough to cover the test tubes when they are in there and placed into the freezer ► Reason for the alcohol is when we come to freeze the yeast, because the alcohol won’t freeze, it will cause the yeast to freeze a little more slowly

When we are ready, and once your kilner jar of yeast has settled out, decant the supernatant leaving around 60ml or so and a gentle swirling for a few seconds to bring the yeast completely back into solution. 3.2 Packaging

3.3 Packaging ► Setup 8 test tubes and using the syringe, fill each one with 6ml of the Glycerine mix. ► I like to loosen the lids first but not remove them so I can get them filled with the Glycerine mix quickly and minimise the tubes being open to the air. ► Needless to say – sanitary is key now. Keep lids on everything as much as possible

3.4 Packaging ► Now do the same with the yeast. Take 6ml of the yeast and quickly inject into one of the test tubes. ► Work swiftly and as sanitary as you can, keeping lids on as much as possible ► You may have to swirl the yeast once or twice as it’ll flocculate out fairly quickly. ► If you can work next to a flame like they do in a laboratory, then even better ► Once all done, tighten the lids and give a gentle shake to mix thoroughly

4. Freeze ► Take your tub of cold isopropyl alcohol out of the freezer, put the test tubes in there and place back in the freezer ► In a day or two (or longer if you forget like me normally) move the now frozen test tubes into a zip lock bag and store back in the freezer until you need one ► Keep the alcohol in the tub ready to freeze your next batch of yeast

Yeast Count ► How much yeast per test tube? ► Many variables and our process is far from perfect ► Typically, a 200ml overbuild is going to be roughly 35-40b cells ► 4-5b cells max per test tube ► I use a figure of 2b cells for new starters in calculators per vial used

Brewfather ► Typical Starter using a packet of liquid yeast/100b cells ► Overbuild by 40b cells ► Overbuild harvest = 200ml

5. Defrost ► When I create a new starter, I simply thaw a vial and add to a ~300ml starter approx 1.020 ► I don’t use a stir plate for this step because I want to be gentle on the yeast, but I will shake the flask every time I walk past ► After a day or so, I’ll step it up to around 1L (depending on what I’m brewing) approx 1.040. I will use a stir plate now for this step ► After another day or so, I’ll either ► step it up again if I’m doing a big beer/lager ► pitch it all into the FV (as-is or cold crash/decant/pitch)

Brewfather calculations ► Two steps should get you to close to 200b cells

Tasting! ► But how does it taste, and does it affect the yeast? ► That yeast starter went on to make a Nectaron pale ale and to make sure it was properly critiqued; I sent a bottle to Ken in May 2024. ► For good measure, Royal Mail lost it in the ”system” for 2 or 3 days before it finally popped back out and landed on Ken’s doorstep ► Ken was aware of the test and focused on the yeast and reported: ► “no off-flavours were detected in that beer”

References ► The Brülosophy Show – “How to freeze yeast (and keep it for years)” (Martin Keen) ► https://www.youtube.com/watch?v=uxnUrDIqN5g ► BYO.com – “The Secrets to Freezing Yeast” (Martin Keen) ► https://byo.com/article/the-secrets-to-freezing-yeast ► Homebrew Notes – “Making a Frozen Stock Yeast Bank” (Adam) ► https://www.homebrewnotes.com/making-a-frozen-stock-yeast-bank/ ► Homebrewtalk - "Maintaining A Healthy Yeast Bank Long Term" (Pete Geisen) ► https://www.homebrewtalk.com/threads/maintaining-a-healthy-yeast-bank-long-t erm.678997/ ► They are all very similar in content