Odds & Ends About Storage of Foods

Here we share some facts on canned and packaged foods, fruits and vegetables and the rotation of foods.

Causes of Food Spoilage

A host of agents can cause food to spoil. Bacteria and parasites in food are a frequent cause of illness. Yeasts produce fermentation, as in fruit juices and cider. Molds attack berries, citrus fruits, breads, jellies and jams and other foods. Chemical changes that cause food spoilage are minimized by avoiding exposure to air or light.

For example, enzymes, normally present in food, bring about chemical changes that lead to softening of the food, development of “off” flavors, loss of some nutrients, darkening of peeled fruit, or rancidity of fats.

Physical factors also produce undesirable changes in food. Milk in clear glass bottles exposed to a few hours of sunlight loses much of its riboflavin and takes on a tallowy flavor. Ice cream held too long in a freezer may become grainy or gummy. Animals or insects may contaminate food with hairs, droppings or insect fragments.

Methods of Food Preservation

Food preservation methods aim to do several things.

  1. Destroy microorganisms, as by heating to sufficiently high temperatures.
  2. Retard microbial growth, as by removing moisture or by cooling to sufficiently low temperatures.

Many molds and some bacteria are known as psychrophilic because they are able to thrive at a relatively low temperature. These microorganisms can grow at refrigerator temperatures and thus can cause foods to spoil even while refrigerated.

Dehydration. One of the oldest methods of preservation eliminates the moist environment that microorganisms need for their growth.

Fermentation. Bacteria in yeasts act on the carbohydrates of fruits and grains to produce acids, alcohol, and carbon dioxide. In sauerkraut, cheeses, and sour cream, lactic acid is produced by the action of bacteria.

Freezing. At zero degrees (-18 C), bacteria and enzymes are inactivated. In the home freezer, foods keep for several weeks or months (depending on the product), with minimum loss of texture, color, flavor or nutritive value. Once foods are thawed, bacteria and enzymes are reactivated and the foods should be used promptly before spoilage can occur.

Freeze drying. This process consists of rapidly freezing the product and then removing the moisture in a vacuum. Examples of foods preserved in this way are coffee, dried soup mixes, and foods prepared for campers, hikers, bikers and boaters.

Heat. The cooking or baking of food leads to destruction of microorganisms and enzymes. Temperatures below the boiling point are not sufficient to destroy some organisms such as salmonella in eggs. Some spores of bacteria and toxins are not destroyed by the heat used in ordinary cooking methods.

Pasteurization is the application of heat to destroy pathogenic bacteria. But it does not sterilze the product. In the high temperature, short time process now widely used, milk is held at 160 degrees for at least 15 seconds. Milk and cream for the manufacturing of cheese, ice cream and butter are usually pasteurized.

Canning is still the primary means used to preserve foods for long periods of time. Home canning is far less frequent than in former times. Meat, poultry, and nonacid vegetables, such as corn, peas, and green beans should be canned only with a pressure cooker for specified times to ensure destruction of the spores of Cl. botulinum.

Chemical Preservation. Sugar and salt are two of the oldest and most widely used preservatives. Sugar has some preservative effect when used in high concentrations for jams, jellies, and preserves. Molds will grow on the surfaces unless the foods are protected from air.

Brine (salt dissolved in water) is used for pickles, sauerkraut, and pickled fish. Sodium benzoate is used in many common food products, including margarine. Sulfur dioxide prevents the darkening of apples and apricots during dehydration. Calcium propionate in bread and sorbic acid in cheese wrapping retard mold growth.

Canned and Packaged Foods

Supermarket foods may have an extended stay on the shelves as well as long warehouse times resulting in reduced potencies of vitamins and minerals.

Fruits and Vegetables:

Usually are harvested before they are fully ripened then allowed to ripen in the markets. Fruits and vegetables are regularly cut into smaller sizes which expose their surfaces to the effects of light and air (oxidation) for long periods of time, thus reducing their nutrient potency.

Rotation of Foods

Canned, frozen and packaged products in the home are rarely dated and rotated properly. Dehydrated foods as well lose a percentage of nutrient potency over time and should be rotated.


Purchase in large quantities, possibly resulting in long storage times, especially if the restaurant is not too busy. Fast food chains avoid this problem due to the faster food turnover.


Excess storage times may result in the purchase of foods thought to contain adequate amounts of certain nutrients only to end up with little or none.

Oranges from supermarkets have been tested and found to contain no vitamin C content, while a fresh picked one contains approximately 180mg. Vitamin and mineral potency losses may occur before the product receives its expiration code date.

A potato in storage for a period of six months can lose approximately 50 percent of its vitamin C content. Most food charts will deduct 25 percent of the nutrient value of foods to allow for the effects of storage, packaging, transportation, processing, preservation and cooking. In some cases this is not enough.

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