Canning Processing of Acid Foods

Canning Processing of Acid Foods
Acid foods are considered to be those that have a pH of 4.5 or lower. Acid foods that are canned need not be heated at high temperatures to attain commercial sterilization. The reason for this is that bacteria, including those that form heat resistant spores, are more easily destroyed by heat when present in acid solutions. Moreover, spore forming bacteria generally will not grow in foods having pH values of 4.5 or less. There are some exceptions to this; for instance, Bacillus thermoacidurans may grow in tomato juice (maximum pH 4.5) and cause spoilage.

Acid foods are ordinarily processed by heating the cans in boiling water until all parts of the product have reached 180 – 210 degree F, and then are cooled. An exception is tomato juice, which is now often processed by flash heating to 250 degree F, holding at this temperature for 0.7 min, cooling to 200 – 210 F, filling into presterilized cans, sealing , and inverting the can so that the sterilizing effect of the heat at that pH will act upon the can cover.

Those foods that have a pH of 4.5 or less are apples and apple juice, apricots, blackberries, blueberries, boysenberries, cherries, cherry juice, a citrus fruit, and their juice, currants, gooseberry, loganberries, papaya juice, peaches, pears, pickles, pineapples in various forms and pineapples juice, plum, prune juice, raspberries, rhubarb, sauerkraut and sauerkraut juice, strawberries, tomatoes, tomato juice and youngberries.
Canning Processing of Acid Foods