Putting Food By - Janet Greene [4]
The term “pH” is an abbreviation in chemistry for “potential of hydrogen,” traced by a sophisticated laboratory device. Crude indications can be made by litmus-like test papers available at scientific supply houses, which can be found on the internet or in the Yellow Pages.
pH RATINGS
This listing indicates in a general way the natural acid strength of common foods on the pH scale. Different varieties of the same food will have different ratings, of course, as will identical varieties grown under different conditions. The Food and Drug Administration now uses a pH rating of 4.6 as the dividing point that dictates the preserving techniques to use: most notably, which canning method is right. Thus foods rated 2.2 (some lemons) on up to 4.6 (virtually every tomato, but see Chapter 8) PFB calls strong-acid—inserting “strong” as a sharper workable distinction than merely “acid,” the customary designation. Foods over 4.6 up to Neutral 7 are always specified as low-acid. Foods over Neutral are alkaline. All low-acid and alkaline foods must be pressure-canned.
The Importance of Sanitation
Even though the spoilage micro-organisms in a food are rendered inactive by cold, they kick in with a vengeance as soon as they warm up.
Or, adequately preheated food can be contaminated by air-borne spores while it, or its unfilled container, stands around unprotected; and, unless it is cooled quickly or refrigerated, the new batch of spoilers can start growing—and growing fast. In this connection, it’s interesting to trace back the notion that one must not put hot food in a refrigerator in order to cool it quickly. This idea is a holdover from the days of the wooden ice chest, which was kept cool by a big block of ice: of course the hot food warmed the inside of the ice chest, and there was a long lag before the ice (or what was left of it) could reduce the internal temperature of the cabinet to a safe-holding coolness. With modern refrigerators, though, a container of warm food merely causes the thermostat to kick on, and the cooling machinery goes to work immediately.
Another good way to deal with the spoilers is simply to wash them off the food as carefully as possible, and to keep work surfaces and equipment sanitary at every stage in the procedure. Food scientists refer to the “bacterial load” in describing the almost staggering rate of increase in bacteria if the food is handled in an unsanitary manner or allowed to remain at the optimum growing temperature for the spoilers. The procedures described in this book have been established after years of research by food scientists, and naturally there is an allowance made for extra micro-organisms that must be destroyed. But in many cases the food would have to be processed almost beyond palatability if the bacterial load had been allowed to increase geometrically to an enormous extent; the alternative of course would be that the treatment was not intensified, so the food spoiled after all.
Household Disinfectants
Boiling water can destroy many organisms if it is indeed boiling and if it has long enough contact with a contaminated surface after it has dropped a hair below the boiling point. Cleaning work surfaces with boiling water is a cumbersome exercise, though; better to use a good household disinfectant, which, for our money, is the liquid chlorine bleach on hand in most kitchens. For an efficient mixture, see Bacterial Load in Chapter 4.
Chlorine dissipates after a while: when you can smell it in the air, it is dissipating. (The best way to rid big-city tap water of too much chlorine is merely to draw a pitcher/bottle of water and let it sit uncovered in the refrigerator for several hours.)
The carbolic-acid-based disinfectants, generally pine-scented, and always milky in solution, are likely to leave their flavor on surfaces.
Heat + Acidity = Canning Safety
Combining (1) the temperatures that control life and growth of spoilage micro-organisms with (2) the pH acidity factor of the foods that are particularly hospitable