Creating a yeast bank is an excellent way to save money and assure that you have happy yeast on hand before brew day. Most of us usually overbuild starters or wash yeast after fermentation. These methods are great but only deal with a single, often large culture of yeast. Banking your yeast allows you to use the same culture multiple times. It also allows you to share your yeast with fellow home brewers. It was awesome of Krzysztof to write up his procedure which is not only easy but all sciency and stuff!
From Krzysztof Lasocki:
The way to do it is to build a permanent stock. What you’ll have in the end is a frozen mixture of wort with fresh yeast and food grade glycerol (easily available). You may need some small equipment, but nothing expensive.
Exactly how to do it is as follows:
1. Make a small fresh yeast culture. When I buy a commercial package (like Wyeast) I prepare a small amount of wort alongside with my starter. You can use the same wort that you are using for the starter, just pour about 1 oz into a small sanitized container. I use regular glass salt and pepper container (you can use whatever that you can easily sanitize and close, preferably something transparent so you can watch the yeast do it’s magic), and cover it with sanitized aluminum foil. Another good idea is to work by a lit alcohol lamp to maintain sterility – very cheap investment.
2. Put it in a warm place for overnight.
3. The next day have sanitized 1.5 ml ready Eppendorf tubes, and food grade glycerin. Make sure that you see microbial growth in your culture (like krausen, murkiness, bubbling, smell). Then, aseptically (by the lit alcohol lamp) mix the fresh yeast culture and glycerol in an Eppendorf tube in the way that the concentration of glycerol will be around 15%. Do not get crazy here – the tube should contain mostly yeast culture with a small addition of glycerol. Make few (like 5 or 6) at a time – for backup in case one is not viable or something like that.
4. Mix it well and freeze it and it’s ready. It should be stable for some time at least
One thing to know: if you have an access to -80 degrees Celsius freezer and the professional yeast medium than you are good for at least 10 years with your stocks. But you probably do not (me too), so I would say every year you will need to re-make your stocks. You do not need to buy new yeast just revive your yeast and make again everything from point 1. So stock only the yeast that you know you are going to use at the regular basis.
I hope it is not intimidating, for me it is really easy but I did that sort of stuff professionally. If you want to proceed I can explain how to revive your yeast from stocks before you want to start fermentation with them. Feel free to private message me or post in the forum.