Yeah, nah, aye

Main categories:

Yeast Ranching

Yeast Ranching is a fancy term for letting yeast multiply well beyond numbers they started out with, then preserving the yeast for later use in wine or beer making. Ranching is typically done by freezing the yeast using glycerine as a cryoprotectant.

It is often used as a cost-cutter and for the nerd-factor. It's a really fun part of homebrewing that I should have started earlier. Just imagine buying a sachet of commercial yeast for $5, then growing it large enough to inoculate 10 batches. Use the last of those 10 to grow another "generation" of 10 samples. Rinse and repeat. Most inexperienced people (like me) stop after 3 generations and start over with a fresh known sample.

I had planned on starting to save extra growth of yeasts I used in mid 2016. I used a fraction of a large yeast starter to make the wine I really bought the yeast for, and I planned to grow the remaining starter up further, ferment it out and preserve it in separate containers for later use in multiple batches of wine in the future.

Life took over and I forgot about the poor starter bottle. It fermented out in mid 2016 and was left there to rot until February 2018, when I felt sorry for the poor thing. Coinciding with the start of a batch of mango wine, I decided I would try to revive the poor old starter while also making a clean starter for the mango wine. The mango wine is going well (too well, I needed more headroom)..

As of today, 2018-02-02, I have started yeast ranching, staring off with a sample of EC1118 that I opened to make some wine.

One of 10 first vials of preserved yeast, just before freezing

Process

I drew lots of information from the good sources on this topic already. Of note is BKYeast's blog which has some interesting information for people at any rung of the microbiology ladder.

My process is fairly simple:

  1. Prepare starter in the normal way (winemaking books all cover this well)
  2. Pitch yeast into the starter, and wait some days
  3. Feed starter with sugar and water as required to reach desired yeast slurry volume
  4. Once nearly fermented out, cool the starter in fridge to drop yeast trub out
  5. Put 3 ml glycerine in vials as cryoprotectant
  6. Sterilise upright in a rack with lids on (but loose) inside a pot of boiling water (see Improvements below)
  7. Sterilise work area with isopropyl alcohol
  8. Prepare bowl of ice water
  9. Open yeast starter
  10. Wipe opening of starter bottle with isopropyl alcohol
  11. Slowly pour off most of the liquid, leaving 1:1 of liquid to trub
  12. Close starter bottle and swish to mix liquid and trub
  13. Re-open starter bottle and wipe opening with isopropyl alcohol
  14. For each vial: open the lid, wipe opening with isopropyl alcohol, add 7 ml of yeast slurry, and re-wipe with isopropyl-alcohol before fitting the lid. Place into ice water
  15. All vials are then frozen at -20 °C inside an ice-jacket container to resist temperature swings that can happen when freezer door left open for prolonged period.

Generation 1 EC1118

One inoculation was never put into a vial, but instead used fresh.

Yeast to fill 10× 10 ml vials of EC1118 was grown in a 1 litre starter bottle. This was fermented until it had a relative density of 1.008. The reason I did this rather than letting it ferment closer to 1.000 was to ensure high cell viability. Fermentation activity had reduced somewhat, and I am unsure of the effect an extra week (time estimated to complete to 1.000) may have had on this.

Generation 1 Neglected EC1118

This is the yeast that was rehydrated and put into a starter in 2016. It is not yet preserved in the ranch. More vials are on order while the starter ferments out the first stage. I will taste- and smell-test the starter in order to determine the quality of the yeast after the abuse it had. If it tastes identical to what I know EC1118 to taste, then I will consider discarding the yeast, since I already have plenty of young EC1118 for the time being.

It does seem a waste to throw away good yeast but I need to prioritise this limited space for other types of yeast before bulking up on any one type. I'm really interested to get some of my staple beer yeasts into the freezer.

Improvements

I have identified some problems and pain points with my process for yeast ranching.

Sterilisation

I do not own a pressure cooker, but it would be far more ideal to use one rather than a pot for the sterilisation step, due to the fact that some bacteria may survive 100 °C heat. This is the top priority on my to-do list.

Water

I am currently using tap water because of its exceptional quality where I live. Still, there is no guarantee for it to be free of contaminants, and distilled water would clean my process up immensely.

Storage Space

I do not currently have a dedicated freezer in which to place the vials, so room is limited. My ice jacket container is inefficient in its use of volume since it is circular.

Ideally, a small-medium chest freezer with boxy ice jacket containers would be used to give a dedicated space for larger volumes of yeast to be stored, and stored more efficiently.

Preservation Temperature

The vials would be better off in a colder freezer, but I doubt I can find a -80 °C freezer cheap enough.