oooFishy

Recipes 

When making starters or a yeast bank, why does everyone get so concerned about sterilization (whooooaa hold on a minute and let me explain). You don't put your carboy in the oven before use to sterile, so why all the extra concern when culturing yeast by themselves? Shouldn't sanitation be sufficient to kill off wild yeast and other bacteria? I mean, this the whole point of iodophor. Will 0.01% of remaining microbes really show up in a culture? Been really trying not to justify unneccesary expenditures. A pressure cooker seems like it may be one of these things...

Funkenjaeger

Recipes 

It never hurts to be extra sanitary when dealing with culturing yeast for storage. When making starters, chances are you're going to be pitching it within a short period of time and the yeast will out-compete everything anyway, so I don't bother going too overboard sanitizing when making starters.

But if you stick a small amount of yeast in the fridge in a slant or whatever, it's not going to be doing more growing - but other organisms certainly can, especially if it's in there for months. I do my culturing without a pressure cooker because I don't have one, but if I did I would use it.

malkore

Recipes 

Sterile is better than sanitized
sanitized is better than clean

plus there are some nasties that are resistent to sanitizers, that would infect our yeast cultures over long periods.
sterilized...they are dead nasties and can't post a threat anymore. basically no room for any mistake...foolproof if you will.

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Malkore
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Iordz

Recipes 

Proper sterilization ensures that all life has been eliminated and gives yeast best possible chance of successfully growing. Believe it or not that .01% of wild yeast and spores that are not killed by the sanitizer can contaminate a sample. Think about it, you're dealing with very small numbers of yeast when you are culturing. Let’s say you have about 100 yeast cells on a slant and because the slant was not sterilized 10 wild yeast cells get in there. The wild yeast will grow faster than the regular yeast and your sample will turn out contaminated. The yeast need to be one step ahead of the bacteria in all situations, at least until there are strong enough to "fight" off small amounts of foreign yeast.
I would say that sterilization is absolutely critical in culturing, all equipment should be sterile and openings of containers should be flamed whenever possible. You don't have to sterilize, but do want to risk a 5gal batch because the yeast was contaminated?

oooFishy

Recipes 

Has anyone actually ever had any contamination issues with a culture with just sanitizing?

Funkenjaeger

Recipes 

I prepare my slants by steaming the filled vials and caps in a steamer basket in a covered pot, long enough for the wort to boil for 10 minutes. Even doing so, I have had one or two blank slants go fuzzy on me after a few months in the fridge, though so far I've been fortunate enough to not have any of my inoculated slants turn south.

It IS a very real concern. since I do not sterilize in a pressure cooker, I always take a close look at inoculated slants before using, to make sure I don't see any obvious nasties.

mrkristofo

Recipes 

I have had bacterial contamination in the lab on yeast/agar plates when the autoclave was down and I sanitized them with bleach/acid. Most unfortunate.

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Chriso

Recipes 

I have not tried this myself yet, as I need to wait for Christmas to get all of my little laboratory goodies for my yeasties, but I have seen others mention before that instead of using a pressure cooker, they instead BAKE any oven-safe pieces at 350F (? or 400F?) for an hour.

More time intensive, yes, but this could be the solution to avoid a 2nd purchase!

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mr x

Recipes 

Use your cooker for a steam heated MLT. Get more bang for your buck.

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david_42

Recipes 

1. Spores are much tougher than live yeast.
2. When pitching, we use very large amounts of yeast relative to possible levels of contamination.

Dry heat isn't as deadly as steam, but 350F for an hour will kill just about anything.

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