Quote:
Originally Posted by coronabarb
Zana,
For the recipes you are posting, please do not post canning recipes that do not give directions for proper water bath processing. If you do not know how much time the jars need to be processed, please say to refrigerate or freeze. Only approved canning recipes can be posted here for safety reasons. I would appreciate it if you would edit the ones already on the board.  |
I've also been taking a close look at pickle recipes and methods, and it turns out that the method called "hot fill/hold" is approved - but only for recipes that are classified as acid foods or acidified foods, with a final product pH of 4.6 or less. The hot fill/hold method brings the pickles to the necessary pasteurization temperatures, so water bath processing isn't necessary. The best description I could find of the process and its limits is here:
www.fapc.okstate.edu/files/factsheets/fapc118.pdf
The size of the pieces of food being pickled is an important factor, where larger pieces might bring the temperature of the boiling brine down below the necessary for pasteurization, and would require a water or steam bath instead.
The same pdf also contains a handy list of the pH of foods that you might be pickling, which would affect the final pH depending on the formula for the brine, pH of added water, and volume and moisture content of raw pickle material.
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.
The second factor for safety in a pickle recipe is "available water" aw, which bacteria require to grow, where water is assigned the value 1.0, fresh foods around .99, and preserved foods have lower aw values depending on the amount of salt and/or sugar used.
Salt is reported to have six times the water binding activity of sugar. An aw value of 0.90 is given to foods with 12% salt or 55% sucrose. A typical 12% salt brine recipe is given as 1/2 cup salt per litre (4.2 cups) water- the 1/2 cup salt/4 cups liquid is a typical ratio I have seen in some USDA approved pickle recipes which also include vinegar. 50% sucrose in recipes is given as approximately 1 cup sugar to 1 cup water.
The salt and sugar in a recipe provides a second line of defense against bacteria, some of which are able to grow at pH lower than 4.6. At available water aw value of 0.90 there is no risk that any of the following will grow in the pickles:
Bacillus cereus, Camplyobacter jejuni, Clostridium Botulinum, Clostridium perfringens, Escherichia coli, Listeria monocytogenes, Salmonella, Shigella, Vibrio spp., Yersinia enterocolitica.
For an aw value of 0.85, I believe it's a 15% salt solution, very salty! and will also inhibit most yeasts as well as toxin formation by
Staph aureus, which has the largest range of pH and salt tolerance among the common food pathogens.
Heat treatment and effective pasteurization is necessary to ensure no pathogens are alive in the sealed product, to multiply while in storage. Botulinum toxin in food can be destroyed by reheating to boiling for 5 minutes, but toxins produced by
Bacillus cereus (min pH 4.3; aw 0.92) and by
Staph aureus (min pH 4; aw 0.83) are very heat stable and cannot be destroyed by reheating. For more about specific pathogens and food handling:
www.hi-tm.com/RFA/food-path-summ.pdf