The Safe pH for Mold Prevention

pH Scale

• Chemicals make up everything you interact with in life. The combination of chemicals cause many things to either be acidic or alkaline. These are two ways of describing a complex relationship between atoms and how they gain and lose ions. For almost everyone not a chemist, the only important information to know is where something falls on the pH scale. A "1" on the scale means something is very acidic, with a "14" meaning very alkaline. A "7" means neutral. So something that is "6" would be slightly acidic, and an "8" means slightly alkaline.

Botulism

• Mold only grows where it's welcome. Normally, that requires a warm temperature, darkness and moisture. For the mold that causes botulism, that also includes the proper pH range above 4.6. If you take the proper steps to ensure the pH level is below 4.6 and inhospitable, the spores that cause the mold have little chance of surviving. Some foods are naturally acidic enough, while others have to have extra acid added to make them safe to can without heat.

Tomatoes

• Tomatoes are the classic example of foods high in acid and normally can be packed without pressure cooking. Not all tomatoes are created equal, though, and some low-acid varieties are dangerous to hot water-pack. For this reason, North Dakota State University recommends that adding 2 tablespoons of bottled lemon juice or 1/2 teaspoon of citric acid per quart of canned tomatoes. This safely reduces the pH level to an accepted amount.

pH Testing

• Other naturally acidic foods often preserved include apples, apricots, beets, blue or black berries, cherries and grapes. Different cultivars can vary in acidity, and the pH of the fruit can also be influenced by the soil it's grown in and the climate. It's always best to test the pH instead of assuming what it should be when hot water-packing the fruit. It costs about $100 in 2011 for a pH meter of sufficient quality for home canning, according to the Minnesota Department of Agriculture.