Quote:
Originally Posted by bower
The pH of the usual 5% vinegar used in pickling recipes is 2.4. Pure water is pH 7.0 but in practice may be above or below 7. A 1:1 ratio of vinegar to water in a recipe would be 2.4+7/2 = 4.7 if the water is neutral pH. So unless the food being pickled is also acid, there's no reason to expect the final pH from this recipe ratio would be 4.6 or less. Recipes with a higher ratio of vinegar to water could be used to provide a margin for error, and reasonable certainty the final pH isn't too high. 4.6 is an important benchmark because it prevents growth and germination of Clostridium botulinum spores. Pasteurization temperatures are also lower, the lower the pH, and the process is expected to kill any vegetative cells of other pathogens and hermetically seal the jars.
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I know this is an older thread/post, but I wanted to point out that the above calculation doesn't work. pH is a log scale, which means you can't simply add and divide like this. In fact, with the above sample information, the end pH if mixed in equal proportions would be 2.7, not 4.7 as suggested.
-log(0.003981mol/L*.5L + 0.0000001mol/L * 0.5L)= 2.7
Mixing vinegar and water in equal proportions is fine, and will prevent botulism, provided the food stuff itself doesn't have significant buffering capacity/alkalinity.
Cheers,
MEB