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Preserving
| 1. Why preserve Food | 2. How Food Preservation Works |
| 3. Costs of Food Preservation | 4. Which Methods of Food Preservation |
| 5. Amounts of Food for Preservation | 6. Preserving Food for Special Diets |
| 7. The Microwave for Preservation |
| Juicy ripe peaches, snapping fresh green beans, freshly
caught flounder and shrimp, crunchy peanuts . . . It's so easy to
preserve-why not save some of these foods to enjoy later, when they
aren't so easy to find?
There are several methods of food preservation from which to choose.
The main methods are canning, freezing and drying. All can
help assure safe food for later, so choose the method that best suits
your needs |
| Unless food is preserved in some manner, it begins to
spoil soon after it is harvested or slaughtered. This spoilage is caused
by microorganisms; physical damage such as bruising, water loss, or
punctures; or by chemical changes such as those caused by enzymes.
The microorganisms that can cause food spoilage include molds, yeasts and bacteria. These microorganisms are everywhere, in the air and soil, on people and animals and on the surfaces of items. They grow well in moist conditions and can easily contaminate foods. Molds appear as fuzz on foods. They grow well on high acid foods such as fruits and most tomatoes (these foods have a pH of 4.6 or less) or on low acid foods such as vegetables or meats (these have a pH over 4.6) (see Chart 1). Molds can be destroyed by temperatures between 140 F and 190 F (see Chart 2). Yeasts also grow in high or low acid environments. Yeasts may cause foods to ferment. However, they are destroyed at temperatures between 140 F and 180 F. Bacteria grow and multiply rapidly on food. They can make food slimy, soft and smelly and they can produce toxins (poisons) that can make you sick. Each type of bacteria varies as to the temperatures at which it can grow. They may grow at cold, warm or hot temperatures. Some bacteria need oxygen to grow, others don't. Most bacteria grow best on low acid foods such as vegetables or meats. Most bacteria are destroyed by heat. However, others form spores that can only be killed by temperatures higher than boiling (212 F at sea level). It's because of one of these bacteria - Clostridium botulinum - that some canned foods have to be processed in a pressure canner where the temperature must reach at least 240 F (see Chart 2). Physical changes also cause food to spoil. Bruising and punctures not only physically damage the food, but in fruits and vegetables, for example, they also provide places where microorganisms can start to grow. Water loss and wilting are other physical ways food spoils. Enzymes are the substances in foods that help them to grow and mature. If the enzymes in fruits and vegetables aren't inactivated, they continue to work after harvest, causing flavor and texture changes. Enzymes can be inactivated by blanching (a short heating period during which the food is held at boiling temperatures for a specified period of time).
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| Canning is the process in which foods are
placed in jars or cans and heated to a temperature that destroys
microorganisms and inactivates enzymes. This heating and later cooling
forms a vacuum seal. The vacuum seal prevents other microorganisms from
re-contaminating the food within the jar or can. High acid foods such as
fruits and tomatoes can be processed or "canned" in boiling
water, while low acid vegetables and meats must be processed in a
pressure canner at 240 F (10 pounds pressure at sea level).
Pickling is another form of canning. Pickled products have an increased acidity that makes it difficult for most bacteria to grow. Pickled products are also heated in jars at boiling temperatures to destroy any other microorganisms present and form a vacuum in the jar. Jams and Jellies have a very high sugar content. The sugar binds with the liquid present making it difficult for microorganisms to grow. To prevent surface contamination after the product is made and thus possible yeast or mold growth, these are either canned, frozen or refrigerated. Freezing reduces the temperature of the food so that microorganisms cannot grow, however some may still live. Enzyme activity is slowed down but not stopped during freezing. Drying removes most of the moisture from foods. Thus microorganisms cannot grow and enzyme action is slowed down. Dried foods should be stored in airtight containers to prevent moisture from re-hydrating the products and allowing microbial growth.
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Costs of Food Preservation
| Preserving food yourself means having an abundant supply
of a variety of foods when the fresh products aren't readily available;
having specialties such as strawberry-fig preserves or green tomato
relish that can't always be purchased; and having the satisfaction of
actually preserving foods yourself. However, preserving food at home may
not save you money.
To determine whether food preservation will actually save you money, you must first consider the cost of the food itself. Food costs vary by season and by source of food. Food given as a gift costs you no money. Growing your own food requires money for gardening equipment, fertilizers, pesticides, seeds and water. Additionally, the time commitment to a home garden is great. However, gardening can be a rewarding family hobby and can supply you with fresh vegetables at their flavor peak throughout the season. Buying food to preserve can be expensive or inexpensive, depending on your source of food and the seasonal availability. Grocery stores are usually the most expensive source of purchasing food. Farmer's markets and pick-your-own farms offer good volume purchase prices when you purchase at the season's peak (quality is best then, too). Other factors that must be considered in determining whether food preservation saves you money include cost of your time, electricity, gas, water, equipment (such as canners, a freezer or a dehydrator), utensils (such as a jar lifter), containers for freezing, containers for dried foods and canning jars and lids. The costs are different for each type of preservation.
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Which Method of Food Preservation to Use
| When deciding which method of food preservation to use,
first consider the costs. Then, you must also consider which method you
prefer to use and which method produces a product that your family
likes. All methods of food preservation can produce safe food for later
use. Some foods, however, are more suited to either canning, freezing or
drying. Others produce an excellent product when any method is used.
Table 1 should help you evaluate the different types of food preservation. For more details on each type of food preservation see each specific section of this book. Chart 1. pH Value of Various Foods
Chart 2. Temperatures for Food Preservation
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Amounts of Food for Food Preservation
| As you preserve food, it is helpful to know how many pints
or quarts of preserved food you can expect from a certain weight of raw
product. Table
2 may help you estimate some of these yields for canning and
freezing.
The yields of canned or frozen foods from raw foods are variable, depending on the maturity and quality of the product, tightness of pack and other factors. Thus the yields given in Table 2 are approximate. Not all the foods listed are suitable for canning and freezing. Consult the sections on canning or freezing for information on preserving each food. Table 3 gives the approximate yield of dried food from fresh. Again these amounts are approximate, depending on the maturity and quality of the product, how much the product is pared or trimmed and so forth. Consult the section on drying for details on drying each food.
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Preserving Foods for Special Diets
| It is possible to preserve food at home for people who are
watching their salt or sugar intakes. Simply, use methods that don't
require sugar or salt for their preservative properties.
If you are preserving food for someone trying to cut sugar consumption, you could can or freeze fruits in water or juice instead of a sugar syrup, or you could dry foods. The sugar specified in canning and freezing is only needed for its effects on flavor and texture. There are also many pickle recipes that call for little or no sugar. Sugar is the major means by which most jams, jellies and preserves are safely preserved. These products are not suitable for a person on a low-sugar diet. However, there are special low-methoxyl pectins and recipes designed to make jams and jellies with no added sugar. It is also possible to preserve foods for someone who is watching their salt intake. The salt used in canning, freezing or drying foods is used only for its flavor or color protection quality. Pickling, especially when fermentation is involved, usually requires salt for its preservative effect. Read the recipe. If it calls for a large quantity of salt, this cannot be eliminated or replaced with a salt substitute. However, if the recipe calls for a large amount of vinegar and only a teaspoon or two of salt for flavor (not soaking), the salt can be left out. (For more details, see the specific sections on canning, freezing, drying, etc.)
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| There are very few uses for the microwave oven in food
preservation.
At the present time, it may be used for making microwave jams or jellies if recipes developed specifically for the microwave are used. However, recipes developed for one microwave may not work in another because of differences between the microwave ovens themselves. Herbs may be dried in small quantities, but unless you. |
All information Courtesy the "University of Georgia - So easy to Preserve Guide ".
CanninAfrica compiled and maintained
by Rosalie Acornley Webmaster.
