CANNING, FREEZING, STORING GARDEN PRODUCE TEXT

Produced by Stephen Hutcheson and the Online Distributed Proofreading Team at http://www.pgdp.net Canning, Freezing, Storing Garden Produce United States Department of Agriculture Agriculture Information Bulletin 410 This is a reprint of Part 4 from the 1977 Yearbook of Agriculture, _Gardening for Food and Fun_. The Yearbook may be purchased at government bookstores or ordered from the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Original page numbers from the entire book are used in this reprint. Contents Part 4 Home Food Preservation _The Whys of Food Preservation_ 298 _How to Minimize Quality Losses_ 304 _Economics of Home Food Preservation, or Is Do-It-Yourself Back to Stay?_ 310 _Beginner's Guide to Home Canning_ 313 _A Primer on Home Freezing for the Beginner_ 320 _Pressure Canners, Vital for Low-Acid Foods_ 323 _Home Canning of Fruits and Vegetables_ 328 _Freezing Your Garden's Harvest_ 334 _Jellies, Jams, Marmalades, Preserves_ 340 _Pickles, Relishes Add Zip and Zest_ 345 _Wine Making (with a note on vinegar)_ 350 _Home Drying of Fruits and Vegetables_ 356 _Storage of Home-Preserved Foods_ 361 _Storing Fresh Fruit and Vegetables_ 365 _Resurgence of Community Canneries_ 372 _Questions and Answers on Food Preservation_ 378 _Food Preservation Glossary_ 383 Issued in December 1977 PART 4 Home Food Preservation [Illustration: Fresh and preserved foods] The Whys of Food Preservation _by Edmund A. Zottola and Isabel D. Wolf_[1] The telephone rings in a county Extension office. A harried voice says, "My garden is growing more than my family can eat, what shall I do with it? How can I keep it from spoiling?" How many times during the gardening season is this scenario repeated in an Extension office? Too often to count! The answers to these questions are readily available in the many bulletins, folders, and leaflets on food preservation available from county, State, and Federal Extension agencies. The publications tell how to preserve food safely and wholesomely, but do little else to explain why directions must be followed precisely. Let's take a look at the whys. To understand food preservation, first consider the sources. Home garden food comes from plants: sources of raw food are living, biological entities, continuing to metabolize after they are harvested. Plants also provide a source of food for micro-organisms which can grow on or in them, spoiling food before it can be eaten. The primary objective of food preservation is to prevent food spoilage by preserving food until it can be used by people. Historically, food preservation and processing assured a food supply and prevented starvation. This is probably the major reason why food is processed today in many developing countries. In the United States, however, affluence and a plentiful food supply now influence the reasons for food preservation. Today, Americans live many miles from rural areas where food is produced. Consequently, food must be preserved to assure the nonfarm population an adequate supply. Our people want a food supply that is safe, high in quality and appearance, adequate nutritionally, and reasonably priced. Many consumers try to obtain these food attributes by returning to the "old ways" of growing and preserving food themselves. To understand food preservation, let's look at five causes of food spoilage or deterioration (four are biological, the fifth physical or mechanical): (1) The primary cause of food spoilage in the United States is microbiological. Micro-organisms are small living organisms such as yeast, molds, or bacteria. They are the chief causes of microbial spoilage. Related to microbiological spoilage of food and also a concern in food preservation is microbiological food-borne disease. There are two types. Salmonellosis is an example of a food infection where food may not support growth of the micro-organisms but merely serves to transfer it from the source to the human host. In the second type, the micro-organism grows in the food and produces a poison or toxin which when eaten, causes illness symptoms. Staphylococcal food poisoning is the most common of the second type in the US. Severity of the major types of food-borne disease in the United States varies from the finality of botulism to the mild discomforts of _Clostridium perfringens_ food poisoning. Food preservation techniques, followed precisely, prevent food-borne disease. (2) The second cause of food spoilage is vermin such as rodents, rats, mice and insects that attack the food and eat or contaminate it before humans can use it. These vermin ruin millions of pounds of food each year. [Illustration: WHAT ELSE CAN WE DO WITH TOMATOES?!!] (3) Have you noticed how an apple, left at room temperature, eventually gets soft, wrinkles, and dries out? This spoilage is called senescence: an aging process caused by continued respiration of the apple, eventually making it useless as food. Other foods also spoil this way. (4) Related to senescence is chemical deterioration of food. The development of rancid flavor in high fat-containing foods is a chemical reaction which brings about an undesirable change. Loss of color or bleaching and loss of vitamins, while food is stored, are chemical deteriorations that can be controlled with proper preservation methods. Both senescence and chemical deterioration are conveyed by organic compounds called enzymes. These enzymes are produced by all living organisms and their function is to speed up or cause the metabolic reaction necessary for the organism's continued existence. The enzymes will continue to act after the plant is harvested, and bring about deterioration of the food unless controlled or destroyed. Preservation methods have been developed to control or destroy these organic catalysts. (5) The last cause of food spoilage concerns food handling. Physical or mechanical damage to the food causes bruising, crushing, cutting, and wilting or water loss. These mechanical defects, besides detracting from the food's appearance, allow easier entry of micro-organisms, insects, and other vermin to cause spoilage and aging. Food preservation processes have been developed to slow down, prevent, or stop completely these processes of food spoilage. An inherent part of food preservation is the package containing the food before or after processing. Packaging provides a convenient method of handling food, prevents contamination during and after processing, bars vermin infestation, supplies a container for storage, and is a necessary part of preservation. An example would be a mason jar with proper seal for pickling. What are the major methods available for home preservation of food? How are they carried out? Why do they prevent spoilage, food-borne disease, and give desired attributes of safety, quality, appearance, nutrition, and economy? The economics of food preservation will be developed in a subsequent chapter. Let's explore the following available methods for home preservation of food: --Control of temperature of the food, heat or cool --Control of the food's acid content --Control of moisture content of the food The major method used for home preservation of food is temperature control. This includes canning with a pressure canner or a boiling water bath, blanching food before freezing, refrigerating food, and freezing it. Micro-organisms which cause disease and food spoilage are sensitive to environment temperature variations. By increasing the food's temperature, micro-organisms are destroyed. When the temperature is decreased, their growth is inhibited. Let's look at the temperature scale illustration and see how temperature affects micro-organisms. To prevent growth of micro-organisms in food and subsequent microbial spoilage, food must be kept out of the temperature range that allows growth. This is most commonly achieved by refrigerating or freezing. Refrigeration slows down or stops microbial spoilage. Freezing stops it completely. [Illustration: EFFECT OF TEMPERATURE ON MICRO-ORGANISMS] Degrees Fahrenheit 225 spore-forming bacteria killed 220-250 proper canning temperatures (low acid foods) 212 water boils; pressure canner needed to obtain temperatures above boiling 170-210 non-spore-forming bacteria, yeasts, and molds killed 120-140 some bacteria can grow 98.6 body temperature 70-80 room temperatures may fall in this range 60-120 DANGER ZONE most bacteria, including food-poisoning types, grow rapidly over this temperature range 32 water freezes 30-60 cold-tolerant bacteria, yeasts and molds grow 0 no microbial growth Enzymatic activity, while slowed down by freezing, is not stopped in many vegetables and these enzymes must be destroyed by blanching the vegetables before freezing to prevent enzymatic deterioration. Successful preservation by freezing must deactivate any enzymes that might be in the food as well as rapidly lower the food temperature to below freezing to stop microbial activity. Freezer burn, a common problem with frozen foods, comes from improper packaging. Food moisture is lost in freezer burn, which results in undesirable flavor and texture changes. Freezer burn can be controlled by proper packaging, proper storing temperature, and avoiding long-term storage. Refrigeration or storage above freezing, but below room temperature, preserves food for days and sometimes weeks. Refrigerated storage slows down activities of enzymes in the food and reduces metabolism of the contaminating micro-organisms. Preservation of food by reduced temperature, refrigeration, or freezing is achieved because enzyme activity and microbial deterioration are slowed down or stopped. Increasing the temperature of food to achieve preservation also results in destruction of the micro-organisms that produce spoilage and disease. Time and temperature regulate this preservation. Theoretically, since food will be stored at temperatures which will allow most microbes to grow, the ideal heat treatment needed to preserve the food would be one that completely sterilizes the food, that is, kills all attendant micro-organisms. To achieve complete sterilization, for example, every particle of food in a jar must reach the required temperature and be held there long enough to destroy all micro-organisms. Heat Transfer The time required for heat to penetrate to the center of the food in a container (the slowest heating point) is extremely important. Heat is transferred through food in containers by two mechanisms: conduction and convection. The mechanism involved depends on the consistency and amount of liquid in the food. The heat penetration rate is also influenced by size of the container, type of heating medium (wet steam vs. dry air), ratio of solid to liquid, kind and size of solid material in container, amount of fat, and amount of salt and sugar. For example, pumpkin or squash can be home canned in two forms: strained or cubed. University of Minnesota research has shown that the time required for the center of a pint jar of strained squash (which heats by conduction) to reach sterilization temperature is three to four times as long as for a pint jar of cubed squash (which heats by convection). The same is true of creamed corn (heats by conduction) and whole kernel corn (heats by convection). Methods and recipes recommended by Extension agencies take into account all of these factors and must be followed precisely to assure a safe and wholesome product. Why is it necessary to heat-process pint jars of string beans at 240° F for 20 minutes in a pressure canner when tomatoes can be successfully heat-processed in a boiling water bath? This brings up the second method of preserving food at home, controlling the food's acid content. This method is most commonly used in combination with heat processing. Most foods contain naturally occurring organic acids. Some foods contain more of these acids and are called acid or high acid foods. These organic acids have the ability to limit, inhibit, or prevent the growth of many of the micro-organisms producing spoilage and disease. The degree of inhibition is related to the amount of acid present. A method used for measuring acid content is called pH. A measure of pH is a determination of the hydrogen ion concentration which reflects the amount of acid or alkali present in the system. A scale from 0 to 14 is used. A pH of 7 is considered neutral, above 7 alkaline, below 7 acidic. Very few foods have a pH above 7. The classification of foods in the acid range below 7 is extremely important. Above pH 4.6 most of the spoilage type micro-organisms can grow, as well as the dreaded _Clostridium botulinum_ (see discussion following on botulism). In foods with a pH greater than 4.6, it is necessary to heat-process the food at temperatures above boiling to obtain the desired level of sterility. There are some types of bacteria that produce entities called endospores or spores which are extremely resistant to environmental stresses. They are a means of assuring survival in bacteria, although not themselves a reproductive mechanism. One growing or vegetative cell will produce one spore, which under proper growth conditions will germinate and produce one cell. This one cell continues to grow and can produce millions of bacterial cells. Destruction of the resistant spore necessitates the use of temperatures above that of boiling water (212° F). _BOTULISM._ One of the most notorious of the spore-forming bacteria is _Clostridium botulinum_. When growing in food this bacteria can produce a deadly poison which causes botulism, a deadly illness. The mortality rate is 56 percent. This bacteria and its spore are present in soil throughout the world and as a result contaminates most of the food we eat. But the spore only germinates and grows where there is suitable food, no air, and a pH above 4.6. These conditions exist in canned low acid foods. To assure botulism-free home-canned foods, it is absolutely essential that low-acid foods be canned in a pressure canner at temperatures above 212° F. The poison produced by this bacteria is one of the most potent poisons known to humans. It has been estimated that 1 cup (8 ounces) is sufficient to kill all the humans on earth. It is not something to take chances about. All home canning procedures recommended by Federal and State Extension agencies are adequate to destroy this dreaded spore-forming bacteria. [Illustration: pH VALUE OF VARIOUS FOODS] High Acid 2.9 plums 3.0 gooseberries 3.2 dill pickles, apricots 3.3 apples, blackberries 3.4 sour cherries, peaches 3.5 kraut, raspberries 3.7 blueberries 3.8 sweet cherries 3.9 pears 4.3 tomatoes 4.6 -------- Low Acid 4.8 okra 5.0 pumpkins, carrots 5.1 turnips 5.2 beets, string beans 5.4 sweet potatoes 5.5 spinach, asparagus 5.6 baked beans 5.7 red kidney beans 5.9 lima beans 6.0 succotash 6.2 peas 6.3 corn 7.0 hominy, ripe olives Commercial canneries, which are regulated by the Food and Drug Administration, use similar processes to assure safe canned foods. In the past 50 years, 75 percent of the reported cases of botulism in the United States have been caused by home-canned food while less than 10 percent have been caused by commercially canned food. If proper home-canning procedures are followed, botulism from this source could virtually be eliminated as a cause of death in the US. On the lower side of pH 4.6, acid content of the food will prevent growth of _Clostridium botulinum_ and most of the other spore-forming bacteria. Thus, these foods can be preserved by using a lower heat treatment. The most common types of spoilage micro-organisms associated with acid foods are yeasts and molds. These organisms are acid-tolerant and can grow in an acid environment. They are killed at a lower temperature than spore-forming bacteria. Acid foods only need a heat treatment in a boiling water bath for a specified time to destroy the microbes present. Fermentation Preservation of food by controlling the acid content can be achieved in two ways. One is to naturally ferment the food--turning cabbage into sauerkraut. The other is to add an organic acid to the food to reduce the pH--adding vinegar to cucumbers to make pickles. Some foods such as berries and fruits naturally contain enough organic acids so their pH is below 4.6, and preservation of these foods requires only a boiling water bath heat treatment or freezing. In a natural fermentation, lactic acid bacteria convert fermentable carbohydrates in the food to lactic acid. In this way the pH is reduced and most bacterial growth inhibited. When cabbage is fermented to sauerkraut, the cabbage's pH is reduced from pH 6.8 during the fermentation to less than 3.5. Cucumbers can also be fermented to pickles by a similar process; however, most pickles are made by direct acidification of the cucumbers. Direct acidification, that is, adding vinegar which contains 4 to 5 percent acetic acid, is the most common method of making cucumber pickles in the United States. It is easier, quicker, and foolproof. Often the natural fermentation will go astray. Other undesirable microbes may grow, bringing unwanted changes in the food: spoiling rather than preserving. Other foods made by fermentation include wine. Regardless of the method used to control the pH of food, to successfully preserve food by this method it is absolutely essential to heat-process or freeze to prevent spoilage by yeasts and molds. An example of spoilage in cucumber pickles not heat-treated after acidification is the development of cloudiness and bubbling. This common spoilage is caused by microbes that would be destroyed by heat processing. Drying Control of the moisture content of food is one of the oldest preservation methods. Removal of water from the food prevents growth of most microbes and slows down enzymatic deterioration. Water removal from food can have several forms. The oldest and most primitive method for removing water is sun drying, which requires long hot days with low humidity to dry food evenly and quickly. Over-drying and uneven drying will result in nutrient destruction, microbial growth, and other undesirable changes. Drying of food in the home can be done and a later chapter tells how. Water activity or availability of water in foods can also be controlled by adding compounds to the food which tie up the water chemically, making it unavailable for use in an enzymatic reaction or for use by the micro-organisms. The two most common home ingredients used in this way are sugar and salt. In making fruit preserves, the high sugar content ties up the water and helps prevent growth of many micro-organisms. Methods used for preserving food in the home are combinations of the