Food Shelf Life

There are only ten minutes in the life of a pear when it is perfect to eat. - Ralph Waldo Emerson

"Shelf-life" is the length of time food will retain most of its nutrition and flavor. Food that may still be safe to eat may have lost much of its nutrition, if stored past its shelf life. Things that cause food to go bad are moisture, oxygen, insects, and animals getting into the food. Good storage containers will most often keep insects and animals out. Already dried foods such as dried beans, white rice, powdered milk, instant potatoes, pasta, white flour, etc. usually don't require additional drying and can be repacked the way they come from the super market. Bulk grains often have higher moisture content and possibly even some insect eggs to deal with.

There are two considerations for quality of stored food.

The Nutritional Life:

A food's nutritional value begins to decline at harvest, there are three basic factors influencing its retention:

  • The food's initial nutrient content.
  • The processing and preservation steps the food underwent.
  • The storage conditions in which it's kept.

The palatability life:

A food's palatability life is when undesirable changes occur to taste, texture, and color qualities. It will almost always be in excess of good nutritive life.

Factors that influence shelf life

  • Tempature Within reason, the key to extending shelf life is lowering the temperature of the area they are stored in. The storage lives of most foods are cut in half by every increase of 18' F. Your storage area should be located where the temperature can be kept above freezing (32' F) and, if possible, below 72' F.
  • Humidity Ideally, your storage location should have a humidity level of 15% or less, but unless you live in the desert it's unlikely you'll be able to achieve this. Regardless, you want to minimize it as much as possible. This can be done by several methods. The first is to keep the area air-conditioned and/or dehumidified during the humid times of the year. The second is to use packaging impervious to moisture and then to deal with the moisture trapped inside.All containers should be kept off the floor and out of direct contact from exterior walls to reduce the chances of condensation brought on by temperature differences between the container and the surface it's resting against.
  • Oxygen Another major threat to your food is oxygen. Chances are that if your foods are sealed in moisture-proof containers the containers are probably air-tight as well. This means that the oxygen can also be kept from doing its damage. If no more can get in, your only concern is the O2 that was trapped inside the container when it was sealed. Lowering the percentage of O2 to 2% or less of the atmosphere trapped inside the packaging (called head gas) can greatly contribute to extending its contents shelf life. The three main tactics for achieving this are vacuum sealing, flushing with inert gas or chemically absorbing the oxygen. Any one or a combination of the three can be used to good effect.
  • Light Light is a form of energy and when it shines on your stored foods long enough it transfers some of that energy to your food. This has the effect of degrading nutritional content and appearance. Fat soluble vitamins, such as A, D, E, and K are particularly sensitive to light degradation.

Assuming they were properly processed in the first place, canned, dried and frozen (never thawed) foods do not become unsafe when stored longer than the recommended time, but their nutrient quality fades and their flavor, color and texture goes downhill. Following these rules of good storage will keep your food wholesome and nutritious for as long as possible:

  • Rotate your storage
  • Cooler is better
  • Drier is better
  • Less oxygen is better
  • Least light as possible