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Canning: A gateway to better health

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Canning: A gateway to better health

Preserving food by heat-treating and then sealing it in airtight containers didn't come along until the late 18th century with the industrial revolution and is still quite popular today.

Canning preserves food by removing the oxygen needed for most microorganisms to grow. This technology is the process of applying heat to food that is sealed in a jar in order to destroy any microorganisms that can cause food spoilage. Proper canning techniques stop this spoilage by heating the food for a specific period of time and killing the microorganisms. During the canning process, air is driven from the jar and a vacuum is formed as the jar cools and seals.

The heating time is designed to destroy any microorganisms that could grow without oxygen (anaerobic). Acidic foods (pH <4.5), such as fruits and tomatoes, naturally contain citric, malic, tartaric, and other organic acids that limit the growth of many pathogens and are less of a concern for food safety. Low-acid foods (pH 4.5–7) such as meat, fish, mixed soups, and vegetables provide a favorable environment for microorganisms and must be canned at higher temperatures. Boiling water reaches a temperature of 212°F (100°C) but water and food in a pressure canner or retort achieve higher temperatures (230–250°F). Time and temperature calculations for canning processes are designed to destroy the most heat-resistant microorganism, specifically the spores of Clostridium botulinum, which can produce a deadly toxin if they sprout and grow under the anaerobic conditions of canned food. Acid foods with pH less than 4.5 can be processed safely at 212°F, the temperature of boiling water because C. botulinum spores cannot grow in acidic conditions.

Two canning methods are approved by the US Department of Agriculture (USDA):

Water-bath canning refers to hot water canning and uses a large kettle of boiling water. Filled jars are submerged in the water and heated to an internal temperature of 212°C for a specific period of time. This method is utilized for processing high-acid foods, such as fruit, items made from fruit, pickles, pickled food, and tomatoes.

Pressure canning uses a large kettle that produces steam in a locked compartment. The filled jars in the kettle reach an internal temperature of 240°C under a specific pressure (stated in pounds) that is measured with a dial gauge or weighted gauge on the pressure-canner cover. Use a pressure canner for processing vegetables and other low-acid foods, such as meat, poultry, and fish.

Botulism is a paralytic illness caused by the ingestion of the toxin produced by C. botulinum; death results from muscle paralysis and respiratory failure. (“Botox” is the application of this nerve toxin for cosmetic and medical purposes.) Clostridium botulinum spores (resistant reproductive bodies) are present in the soil and can contaminant fruits and vegetables. Spores will not germinate in the presence of oxygen or in acidic conditions but can germinate in sealed jars of low-acid foods such as asparagus, green beans, beets, and corn, if not destroyed by temperatures above boiling achieved under pressure during the canning process. The food industry is highly regulated to ensure canned foods are processed correctly to avoid this contamination. Home canning of foods can be a risk if not done properly. Properly preserved canned food is safe and wholesome for consumption for months and even years.It is essential that proper canning techniques and equipment are used to avoid food-borne illness when doing home canning. Methods such as heating jars of food in the oven or even a dishwasher are unsafe and very risky.

The heating used to process canned foods does change the color, texture, and flavor of foods. Also, salt may be added to canned vegetables or sugar to fruits to retain color and texture. Many consumers prefer the firmer texture and more intense flavors of frozen or fresh foods over canned foods and may want to avoid added salt or sugar. New technologies to reduce the amount of heat used to preserve food, such as aseptic heating, are being developed.

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