Acidifying wort used in slants to allow sterilisation at boiling temps

[Simonh82]

My understanding is that the reason the wort used in slants should be boiled in a pressure cooker under 15PSI of pressure is to raise the temperature high enough to kill botulinum spores. I've only made a couple of batches of slats so far and as I don't have a pressure cooker I've just boiled the wort for 30 minutes. So far so good, I'm not dead yet. Still, I'd like to avoid botulism if I can.

My understanding is that the reason we need to use pressure, as well as heat, is because low acid foods are more susceptible to botulism, whilst high acid foods can be treated with a normal boil. The stated boundary between high and low acid food is a pH of 4.6. So, could you not just acidify the wort to 4.6 or lower, which is where yeast like to be anyway and then boil normally?

 

[Simonh82]

Any thoughts?

 

[Queequeg]

Slants are aerobic so c.botulinium will not grow. Also the spores aren't killed by the low pH conditions they just won't vegetate.

Sterilisation is a a factor of time and temperature. The need for presurization is an artefact of requiring a temperature greater than 100°C for some spores.

Since Clostridium species are anaerobic they is no risk of proflieration during cultivating yeast on slants and aerated starters. Any spores that are transferred to the fermenter with not vegetate as the pH will be too low after the O2 is sufficiently depleted.

You are more at risk from bacillus spores contaminating your slants because bacillus subtilis for example is aerobic, ubiquitous and will survive up to 110°C. Then again you will know straight of because it will out grow the yeast and have a very distinctive smell.

 

[ESBrewer]

Yes, the sterilizing conditions are more for destroying all the possible spores of bacteria than to prevent Clostridium botulinum specifically. If you are very lucky, you may be able to have success at 100°C, but contaminations may occur without higher temperatures that can be obtained by a pressure cooker. If you are interested in culturing yeast at home I would encourage to buy a pressure cooker. There are decent small cookers that are affordable for prepqaring slants, plates and small volumes of wort.