Canning is an important and safe method of food preservation if practiced properly. The canning process involves placing food in jars and heating the jars to a temperature that destroys microorganisms that could be a health hazard or cause the food to spoil. This heating also destroys enzymes that may cause undesirable changes in the flavor, color, and texture of vegetables. Air is driven from the jar during heating, and as it cools, a vacuum seal is formed. The vacuum seal prevents air from getting back into the product, bringing with it microorganisms that would recontaminate the food.
CANNING BASICS
Botulism warning
With the exception of tomatoes (a fruit that is marketed as a vegetable), all vegetables are low in acid and have a pH value of greater than -1.6. These low-acid vegetables support the growth of the bacterium Clostridium botulinum when given the right conditions, which include moisture, room temperatures, lack of oxygen, and low-acid conditions. When growing. Closu iilium bolulimtm produces an extremely potent toxin that causes the illness botulism in people even though the food may taste and appear normal. If untreated, botulism can cause death within a few days of consuming the toxic food. Follow the directions below to make sure your canned foods are safe.
Select the right canner for each food
There arc iwo safe methods of canning: water-hath (boiling-water) and pressure canning. Which one to use depends on the type of food being canned. High-acid foods such as most fruits, tomatoes, and pickled vegetables, as well as jams, jellies, and other presents, can be safely processed using a water hath canner. Consult the resources listed in "For More Information' at the end of this publication for instructions on safely canning acidic foods using a water-bath or boiling-water canner.
Pressure canning is the only safe method for canning low-acid vegetables. Clostridium bottlffnum is not killed hy boiling water (212°F. 100°C). A water temperature higher than boiling is necessary to kill the bacteria and safely process low-acid foods in a reasonable length of tune. Pressure canners typically operate at a temperature of at least 240°F (116"C), which can be achieved only at pressures of greater than 10 pounds per square inch (69 Pa).
Pressure canners
A pressure canner is a specially made heavy pot with a lid that can be tightly closed to prevent steam from escaping. The lid is fitted with a vent, a dial or weighted pressure gauge, and a safety valve (figs. I and 2). Because each type of canner is different, read the manufacturer's instructions on the care and use of your pressure canner. For safe operation of your pressure canner. clean the petcock or vent pipe and safety valve openings by drawing a clean siring or narrow strip of cloth through them. Do this at the beginning of the canning season and often during the season. The pressure dial gauge on a canner should be checked for accuracy on a yearly basis. Refer 10 the manu Hirer's instructions or contact your local University of California Cooperative Extension county office for further information.
Preparation of vegetables
Select fresh, firm, crisp vegetables. Prepare vegetables in batches that will just fill the jars required for one load of your pressure canner. Wash and prepare the vegetables according 10 the directions in table 1. When precooking for the hot pack method, use a minimal amount of water. This water can be used as the covering liquid in the jars.
Canning without salt
ll is not necessary lo add sail for safely when canning vegetables, is added for flavor and can sometimes help retain texture.
Glass jars
Make sure all jars are free of cracks and chips. These defects will prevent airtight seals. Jars that are manufactured for home canning arc recommended. Mayonnaise jars and similar jars are not recommended for use in home canning because they are not manufactured for repeated heating and have a higher rate of breakage, particularly in pressure canners. Wash glass jars in hot, soapy water and rinse, or wash them in a dishwasher.
Lids and rings
For lids, select the size that fits your jars. Always use new lids each time you can. Follow the manufacturer's instructions for pretrcating the canning lids. Metal lids have a sealing compound and usually need to be heated prior to use. Rings can be reused if they arc in good condition. Wash and thoroughly dry the rings before storing and they will remain in good condition for years.
