The definition of pH
is the “potential of hydrogen” – it is the amount of acidity (or alkalinity)
in a food (solution). pH has a numerical scale from 0 to 14.
pH Scale: 0 = strongly acidic, 7
= neutral, 14 = strongly basic (alkaline)
For home food preservation:
pH ≤4.6 = food is high acidity (suitable for water bath
canning)
pH ≥4.6 = food is low acidity (suitable for pressure
canning)
Note: The pH scale is logarithmic, which means that each
whole pH value below 7 is 10 times more acidic than one whole pH value above
i.e. pH 2 is 10 x the acidity of pH 3, and 100 x the acidity of pH 4. This is important because if your water bath canned food is "a little over" the safe pH for water bath canning, it may be a big difference in "real life" and jeopardise the safety of your preserved food.
High acid food has
a pH of 4.6 or less
Acidic food is
processed in a water bath canner. Acidic food can be naturally acidic (like
most fruits) or have acid added to vegetables to create pickles, chutney,
relish and salsa. Tomatoes and figs also require acidification before canning,
as some varieties have a pH slightly above 4.6. Acids added to food include vinegar,
lemon juice or citric acid.
Low acid food has
a pH above 4.6
Low acid food must
be processed in a pressure canner. Meat and vegetables are two examples of low
acid food suitable for pressure canning.
Boiling
water temperatures will not destroy Clostridium botulinum spores – the acidity
(pH) can stop them multiplying and prevent the production of neurotoxins if the
pH is 4.6 or lower. The canning process (temperature +
processing time) can then remove any other microorganisms that cause spoilage.
When testing pH for
canning, it must be done correctly and accurately. We will discuss how
to do this next.
Author: Megan Radaich
Image Credit: https://www.ibchem.com/IB16/08.31.htm
Publication: www.foodpreserving.org