Canning basics 1: Introduction
Why people can foods
Canning can be a safe and personally rewarding way to preserve quality food at home. Canning favorite and special products to be enjoyed by family and friends often is a fulfilling experience and a source of pride for many people. Canning may not be the least expensive way of obtaining every type of food and costs of equipment, energy, and time must be considered.
However, the main objective of canning is to preserve the food by the application of heat so that it can be safely eaten at a later time. Safety of the consumer is the primary concern when food is canned. It is also important to achieve acceptable quality in the final product and to retain as much of the nutritive value of the food as possible. The potential advantages of home canning are lost 1) when you start with poor quality fresh foods, 2) when jars fail to seal properly, 3) when food spoils, and 4) when flavors, texture, color, and nutrients deteriorate during prolonged storage in warm, bright light conditions.
The nutritional value of canned food
Many vegetables begin to lose vitamins when harvested. Nearly half the vitamins may be lost within a few days unless the fresh produce is cooled or preserved. Within one to two weeks, even refrigerated produce may lose half of its vitamins. The heating process during canning destroys from 1/3 to ½ of vitamins A and C, thiamin, and riboflavin. Once canned, additional losses of these sensitive vitamins are from 5 to 20 percent each year depending on storage conditions. The amounts of other vitamins, however, are only slightly lower in canned compared with fresh food. Vegetables handled properly and canned promptly after harvest may be more nutritious than fresh produce held many days after harvest under abusive conditions.
How canning preserves foods
The high percentage of water in most fresh foods makes them very perishable. They spoil or lose their quality for several reasons:
- growth of undesirable microorganisms such as bacteria, molds, and yeasts
- activity of food enzymes
- reactions with oxygen
- moisture loss
Microorganisms live and multiply quickly on the surfaces of fresh food and on the inside of bruised, insect-damaged, and diseased food. Oxygen and enzymes are present throughout fresh food tissues. Proper canning practices minimize the effects of these microorganisms. They include:
- carefully selecting and washing fresh food
- peeling some fresh foods
- hot packing many foods
- adding acids (lemon juice or vinegar) to some foods
- using acceptable jars and self-sealing lids
- processing jars in a boiling-water or pressure canner for the correct period of time
When these practices are followed along with recommended methods, they control potential spoilage by removing oxygen, destroying enzymes, destroying and/or preventing the growth of undesirable bacteria, yeasts, and molds, and by helping form a high vacuum in jars. Good vacuums form tight seals which keep the food in the jars and keep air and microorganisms from reentering.
The most critical step in ensuring safety in canning is processing in a boiling-water bath or pressure canner. This is what destroys microorganisms and creates the desired vacuum for a good seal. Both a high temperature and sufficient time is required to be certain of adequate heat processing. This ensures that all parts of the food being canned have received enough heat to reduce the number of microorganisms to an extremely small level. A safe food with a long storage life is produced. The complete destruction of every microorganism would result in a product with unacceptable quality and little nutritional value. A best process is that which has a maximum effect on spoilage organisms and minimal effect on quality.