The process of making a frozen yeast bank might be apparently super-complex and scientific but it’s such a cakewalk if you get your hands on the items mentioned below.
- a pressure canner
- two Mason jars
- a 50 pack of 15 ml sterile test tubes
- vegetable glycerine of USP grade
- three lbs of dry malt extract
- a spray bottle of sanitizer
- a measuring cup
- an insulated box or your insulated lunchbox (pick a box that matches with your freezer’s size to fit in)
- and some gel ice packs that can be reused
Now, here are the optional items. A hand towel, a test tube rack that can hold 50 tubes, and a 50 pack of 6 ml oral syringes.
Don’t forget you’re not making yeast samples to ferment just a single batch of beer. They’ll be used to ferment the coming beer batches too. So, just try to stay as hygienic as an individual with OCD. Ensure everything you use is well-sanitized throughout the process to keep infections at bay.
Make Cryopreservative to Freeze Yeast
Always keep your yeast in the refrigerator and not in the freezer. While the yeast is freezing, it gives birth to ice crystals that are kind of unfaithful to rupture the yeast cell walls and killing most of the yeast. Well, you can keep them for short term storage, that’s alright but never keep the yeast in the fridge for a long time.
So, here comes cryopreservative to the rescue of the yeast. Mix your yeast slurry with it and the formation of ice crystals will minimize.
How to Make Cryopreservative?
The items that come in handy to make Cryopreservative are glycerine, a pressure canner, a measuring cup, a short or wide Mason jar with a wide mouth. Got these items?
Now, let’s make cryopreservative and help the yeast fight back the ice-crystals.
Take 25% glycerine and 75% water in a pint jar and make a solution. Okay, don’t do the math if you are that guy who multiplies both sides by zero to prove LHS=RHS. Just take 2.5 oz or 75 ml of glycerin and 7.5 oz or 225 ml of water. Now, pressure can the jar for ten minutes.
Once it’s pressure canned, let it cool down to the room temperature eventually. Please don’t place the jar in a cool water tub or water bath because you don’t want to get injured. If you do so, the jar cracks. Just scroll your newsfeed, contemplate your life’s purpose, or brew some beer while you wait, but be patient. It’ll calm down in few hours and yeah, all set to use it now. Just use it whenever you need and seal it tight right then so that it can be used for a prolonged period.
This full process is broken down in this video here: (2:43-6:06)
How to Make a Yeast Starter
You’ll need to make a yeast starter to expand the yeast further and continue with this process.
Alternatively a fast-pitch yeast starter will do just fine.
You’ll need a wide-mouthed mason Jar that’s short or wide, a 50 pack of 15 ml sterile test tubes, freezer-proof container, a well-sealed plastic bin, Isopropyl alcohol that has more than 90 % alcohol, a bottle of sanitizer spray, a fine-tipped marker, a 50 pack of 6 ml oral syringe, recyclable gel ice packs, a lunch cooler box or an insulated box that fits in your freezer. The optional items are masking tape, a hand towel, and a test tube rack of 50 tube capacity.
Take a pot that’s double the size of starter volume, add some amount of water that’s the same as starter size volume. Heat it on medium flame to make it hot but not boil.
Keep adding the dry malt extract (DME) by stirring, so the lumps can’t be formed and set the flame high. Once it boils, do lower the flame (else it’ll get super-sticky). Turn it off after 10 minutes and cover the pot.
Now place the pot (don’t remove the cover) in a water tub to cool it down until it reaches the fomentation temperature.
No sooner than your starter is ready, be onto the yeast banking. Sit on a chair to be stable and spread out a hand towel for easy clean-up if you’re a bit messy like me. Place 10 test tubes in a tube stand and keep them closed so they remain sterile.
Now, sanitize the wide-mouthed jar and pour the decanted yeast into this smaller vessel so that it’ll be easier to work. Sanitize the jar’s lid and cover it.
Now, before you do anything be mindful of being quick and not exposing the yeast to the open air (bacteria) for consecutive minutes. Open five test tubes and yeast slurry jar. Take a 6ml oral syringe (sanitize if it’s not vacuum-sealed), let it suck 5-6 ml of yeast slurry, and then squirt gently into the five tubes. Cover these, open the other five tubes, fill them in the same way and cover them too.
Extract 5-6 ml of cryopreservative from the jar (sanitize the syringe again and again) and gently eject it into all the five tubes. Sit your syringe down, cover those tubes, and repeat the same with the other five with a sanitized syringe. (Close the Cryopreservative jar once you’re done using)
Shake the tubes so that cryopreservation and yeast get mixed up well. Woah! You just made yeast samples in about 10 minutes.
How to Freeze the Yeast Bank
Now, immerse your yeast sample test tubes in a plastic bin and put all the other test tubes in it. Pour some isopropyl alcohol into it to fully swamp the samples and then, close the bin. Put masking tape on the bin lid and write yeast name, number, and the date so that it’ll be okay if you forget them. (It’s optional though)
Put the bin in the freezer and leave it for a minimum of 24 hours, rather 48. Use that time for altering your yeast banking station.
After a day or two, start taking out the tubes one by one, wipe and dry them with the hand towel. Take a marker and write yeast number, name, and date on them.
Place your new frozen yeast bank starters in the test tube rack and then in the freezer. Its ideal to use an insulated box to protect the yeast from the rapid defrosting temperatures, but isn’t neccessary.
And that’s it! You’ve made a frozen yeast bank that can’t be spoiled for many a year.