G'day Drs, About while ago I was bottling a batch of hefeweizen and wanted to reserve some yeast from it. My method was to rinse about 100mL thick yeast slurry in cooled boiled water once or twice, removing as much trub as possible, before leaving it under a 300mL layer of cooled boiled water and storing in the fridge at 1C. The strain was White Labs Hefeweizen (WLP300).

I didn't intend on leaving it so long, but today, about 7 months later, I made up a 250mL batch of ~1.035 SG wort with some Wyeast nutrient and pitched it onto the yeast (I poured off the water first). It's in a small plastic bottle and I am squeezing air in and shaking it to introduce as much O2 as possible. It's now fermented out so something is alive.

If I wanted to use this yeast, which I probably don't, what would be your suggestions as for how to build up a healthy crop of yeast for pitching? I'm not yet at the plating and culturing stage, and I realize that this would be a good method, but what else can I do?

I realize this is probably not anything you'd recommend to the public, but I'd like to know if in desperate times that there's something you can do to save very old yeast.

Thanks,
Stuart Grant

RESPONSE:

Stuart, Under your circumstances you did the right thing. You can store yeast under water for longer period of time. But it is critical, as Dave pointed out, that you wash your yeast thoroughly and remove all residual sugars and that you store the yeast as cold as possible without freezing them.

Once you decide to reuse the yeast again you should build up a starter culture, like you did, because you will find a higher concentration of dead cells after extended storage. But with the remaining viable cells you should be able build a good starter if you pamper your yeast with oxygen and nutrients (FAN, minerals)

Regards,
Tobias & Forbes