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Can botulism spores grow in concentrated extract?

TroubleShooting

Ken Graffis • Hendersonville, Tennessee asks,
Q

The recent discussion in Brew Your Own of preserving starter wort and the safety of the practice has raised (in my mind) several questions on the safety of my malt extract storing practice. Shortly after beginning brewing 18 months ago, I discovered that extract could be purchased in 15-kilogram plastic jugs for half the price per pound of canned extract. Being of a frugal nature, I immediately began buying in this quantity. After opening a jug to make a batch of beer, I pour the excess in plastic tubs and top with a splash of vodka to inhibit mold growth and store in my fridge at about 40 °F (4 °C). Can botulism spores ever grow in concentrated extract with its high sugar content? I assume the jugs I buy are not pressure canned because they are plastic. Quality questions aside, how long can I safely store extract in this manner? Would freezing have any effect on its quality?

A
  Before answering this question about malt extract storage I want to remind our readers that there are no safety issues concerning the storage of wort that has been properly canned in
Response by Ashton Lewis.