[jeffy]

Well, you're supposed to boil it again.

I think that depends entirely on your level of bravery.  If the wort was boiled and then put into a sanitized bottle or jar, then refrigerated, don't you think you could add it right to your yeast when you need to make a starter?
I saved some almost boiling hot low-gravity wort in sanitized 12 ounce bottles which I capped and refrigerated.  It makes for an easy, no boil starter.

[tygo]

The attraction to me of canning would be having sterile wort on hand for quickly making starters without boiling.  I don't think I'm brave enough to store in the freezer and not boil it before using it in a starter.

[ajk]

Why not just freeze it instead of canning it? If you can it you don't need to put it in the fridge.

The concern is botulism.  Boiling or freezing alone won't kill the spores that cause it.  That's why people use a pressure cooker to can food (boiling temperature is higher under pressure, high enough to kill the spores).

That said, I'm not sure I share the concern.  We don't worry about spores in finished beer, presumably because of the lower pH and the alcohol.  So if this wort eventually becomes finished beer, what's the danger?  Maybe that the spore count will be too great by then for the pH and alcohol to bring it down to the (very low) level tolerable by humans ...

[Hokerer]

Why not just freeze it instead of canning it? If you can it you don't need to put it in the fridge.

The concern is botulism.  Boiling or freezing alone won't kill the spores that cause it.  That's why people use a pressure cooker to can food (boiling temperature is higher under pressure, high enough to kill the spores).

That said, I'm not sure I share the concern.  We don't worry about spores in finished beer, presumably because of the lower pH and the alcohol.  So if this wort eventually becomes finished beer, what's the danger?  Maybe that the spore count will be too great by then for the pH and alcohol to bring it down to the (very low) level tolerable by humans ...

That is the concern.  The low pH and alcohol will prevent growth of any more toxin but it has no affect on what might already be present.  If you're going to be using the wort within a very short time, then freezing is probably save as there wouldn't be enough time for toxin growth.  But if you're going to be saving it for any significant amount of time, pressure canning is the way to go as that guarantees that there're no spores to generate toxin.

For me, I prefer to play it safe and pressure can all my starter wort.  It really takes very little effort.

[richardt]

It is Botulinum toxin, not so much the spores, that we should be concerned about when talking about food-borne botulism.
For food safety reasons, I'd recommend boiling your starter wort (and cooling it down to pitching temps) before pitching the yeast.
Regardless of storage method (refrigeration vs freezing, pressure cooked mason jars vs sanitized plastic jugs, etc.), boiling the starter wort will inactivate any botulinum toxin that may have been produced during storage.  And boiling is an easy way to sanitize the flask and aluminum foil covering, as well.

[tschmidlin]

If the wort came straight from the boil, was chilled and then frozen there would be no more botulinum toxin in it than if it was chilled and used right away.  It's not like the C. boutlinum (assuming they're even present) are going to be growing and creating toxin at 0F, which is where most freezers are set.  If you want to store it at room temp then yeah, use a pressure cooker.  But if you're freezing it I don't see the need.

[jeffy]

If the wort came straight from the boil, was chilled and then frozen there would be no more botulinum toxin in it than if it was chilled and used right away.  It's not like the C. boutlinum (assuming they're even present) are going to be growing and creating toxin at 0F, which is where most freezers are set.  If you want to store it at room temp then yeah, use a pressure cooker.  But if you're freezing it I don't see the need.

Whew!  These guys were beginning to worry me!

[tschmidlin]

Whew!  These guys were beginning to worry me!

That might be a good thing Jeff.   

You mentioned you keep yours in the fridge - what temp is it?  Some strains of botulinum can grow at fridge temps if it's too warm, something like 38 or 39F.  To make matters worse, those strains don't break down proteins and so they may give no indication of contamination, ie it won't necessarily smell off.  I'd turn it down to 35, freeze it, or boil the refrigerated wort before using it.

[jeffy]

OK, thanks, Tom.  I wasn't quite dead yet.