Beer Forum

So here's a simple question with a potentially complicated answer: Short of cryogenic storage what's the best method for long-term yeast culture banking with while reducing strain mutation rates to a minimum?

Better yet, what's the best method that can be done in the home environment (using sanitization best practices, of course)?

Agar slants: http://morebeer.com/view_product/19903//Slants_-_Malt_Agar_Filled

Slants are really medium term storage (by our standards) 3-6 months.

For longer term storage some people will advocate distilled water, some a 10% sucrose solution, or stabs (sorta like a slant but the yeast is stabbed into the agar instead of streaked on a slanted surface).

All of these should be suitable for a few years.

Pierre Rajotte advocates the sucrose solution and Mary Beth Raines the stabs. I don't recall where I read about the distilled water storage but it seems to work and in theory does what the sucrose solution is trying to do but better (keep the yeast alive but preventing them from reproducing).

You need to be using good sterilization practices with any of these.

I'm not a yeast expert, but my sources tell me that stabs only increase viability for a short time compared to slants. The purpose of a stab is to reduce the amount of air in contact with the organism being cultured, but yeast grow anaerobically. They will still grow slowly, and you still run the risk of mutation over time as the White's said the other day.
IMO your best bet is a sterile 10-20% glycerol solution stored at as low a temperature as possible. -80C would be great, but -20C will still last longer than slants.

BayouBrew wrote:I'm not a yeast expert, but my sources tell me that stabs only increase viability for a short time compared to slants. The purpose of a stab is to reduce the amount of air in contact with the organism being cultured, but yeast grow anaerobically. They will still grow slowly, and you still run the risk of mutation over time as the White's said the other day.
IMO your best bet is a sterile 10-20% glycerol solution stored at as low a temperature as possible. -80C would be great, but -20C will still last longer than slants.

Well sure, if you have access to a -80C freezer! Might as well stick it in the -140C liquid Nitrogen

BayouBrew wrote:I'm not a yeast expert, but my sources tell me that stabs only increase viability for a short time compared to slants. The purpose of a stab is to reduce the amount of air in contact with the organism being cultured, but yeast grow anaerobically. They will still grow slowly, and you still run the risk of mutation over time as the White's said the other day.
IMO your best bet is a sterile 10-20% glycerol solution stored at as low a temperature as possible. -80C would be great, but -20C will still last longer than slants.

Well yeah, freezing would be great. For most of us the easiest method of storing yeast cultures frozen is to let a vendor do it for us.

I would expect the same yeast growth in a stab and a slant, but still think the lack of air exposure in the former is advantageous. Perhaps the advantage is so marginal over slants to render the practice practically useless.

remilard wrote:Well yeah, freezing would be great. For most of us the easiest method of storing yeast cultures frozen is to let a vendor do it for us.

True, but then you're putting your recipe in the hands of your yeast providers and, let's face it, yeast are a unique product and if your supplier goes under you're pretty much screwed. Is it likely to happen? No, but the mere chance that an irreplaceable strain can get lost or cease commercial production would make long-term, minimal mutation storage a wise idea.

Plus, it's an excuse to tack on when I tell the wife I'm getting a microscope...

Frankenhop wrote:Plus, it's an excuse to tack on when I tell the wife I'm getting a microscope...

Add the "I'm saving money in the long run.." card.