Putting Food By - Janet Greene [2]
CONVERSIONS FOR PUTTING FOOD BY
Do look at the conversions for metrics (with workable roundings-off) and for altitude—both in Chapter 3—and apply them.
How Enzymes Act
Nature has designed each plant or animal with the ability to program the production of its own enzymes, which are the biochemicals that help the organism to ripen and mature—in short, enzymes promote the organic changes necessary to the life cycle of all growing things. However, their action is reversible: they can turn around and cause decomposition, thereby causing changes in color, flavor, and texture, and making food unappetizing.
Their action slows down in cold conditions, increases most quickly between around 85 to 120 degrees Fahrenheit/29 to 49 degrees Celsius, and begins to be destroyed at about 140 F/60 C. However, the natural enzymes in some foods, notably cucumbers, are especially tough. Thus, in making pickles, the heat resistance of enzymes is as much of a concern as the heat resistance of bacteria, molds, and yeasts, all of which are controlled not only by the heat of the processing bath but also by the acid of the vinegar-loaded pickling solution.
How Molds Act
Molds are microscopic fungi whose dry spores (seeds) alight on food and start growing silken threads that can become slight streaks of discoloration in food or cover it with a mat of fuzz.
It used to be felt that “a little mold won’t hurt you,” but modern research has disclosed that only the mold introduced deliberately into the “blue” cheeses like Roquefort, Gorgonzola, or Stilton is trustworthy. The others, as they grow in food, are capable of producing substances called mycotoxins, and some of them can be hurtful indeed.
In addition, molds eat natural acid present in food, thereby lowering the acidity that is protection against more actively dangerous poisons—but we’ll have more to say about this in a minute.
Molds are alive but don’t grow below 32 F/Zero C; they start to grow above freezing, have their maximum acceleration at 50–100 F/10–38 C, and then taper off to inactivity beginning around 120 F/49 C; they die with increasing speed at temperatures from 140–190 F/60–88 C.
How Yeasts Act
The micro-organisms we call yeasts are also fungi grown from spores, and they cause fermentation—which is delightful in beer, necessary in sauerkraut, and horrid in applesauce. As with molds, severe cold holds them inactive, 50–100 F/10–38 C hurries their growth, and 140–190 F/60–88 C destroys them.
How Bacteria Act
Bacteria also are present in soil and water, and their spores, too, can be carried by the air. But bacteria are often far tougher than molds and yeasts are; certain ones actually thrive in heat that kills these fungi, and in some foods there can exist bacterial spores which can make hidden toxins. These spores will be destroyed in a reasonable time only if the food is heated at 240–250 F/116–121 C—at least 28 degrees higher than the boiling temperature for water AT SEA-LEVEL CLASSIFICATION, and obtainable only under pressure.
Of the disease-causing bacteria we’re concerned with mainly, the most fragile are members of the genus Salmonella, which are transmitted by pets, rodents, insects, and human beings, in addition to existing in our soil and water. Salmonellae live in frozen food, are inactive up to 45 F/7 C, and are killed when held at 140 F/60 C for 3 minutes, with destruction almost instantaneous at 165 F/74 C.
The transmittable bacteria that cause “staph” poisoning, the Staphylococcus aureus, are responsible for the most common type of food-borne illness, the sort formerly attributed to “ptomaines.”