Principles to Remember

The science of preservation comes down to controlling a few key variables:

• Water activity below 0.85 prevents most bacterial growth — this is why jerky, raisins, and crackers last
• pH below 4.6 stops Clostridium botulinum, which is why acidic foods are safer to can at home
• Temperature below -18°C halts nearly all microbial activity but does not kill bacteria — they wake up when food thaws
• Oxygen removal prevents aerobic bacteria and slows the oxidation that causes rancidity
• Chemical preservatives like sodium benzoate and potassium sorbate are acids that disrupt microbial cell membranes