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!
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.
OK, thanks, Tom. I wasn’t quite dead yet.