Iron and copper from cooking utensils or from water in some areas may cause brown, black, and gray colors in some foods.
Why do undersides of metal lids sometimes discolor?
Natural compounds in some foods, particularly acids, corrode metal and make a dark deposit on the underside of jar lids. This deposit on lids of sealed, properly processed canned foods is harmless.
Is it safe to use canned foods which have been frozen as the result of storing them in an unheated storage area?
Freezing does not cause the food to spoil unless the seal is damaged or the jar broken. If the jar is no longer sealed, the food may still be safe to eat if the jar is not broken and the food is still frozen and has not been subjected to thawing and refreezing.
Remove the frozen canned food from jars as carefully as possible. The food may need to thaw slightly to ease its removal from jars, but it should be left in as large blocks as can be removed through the jar opening.
Examine jars for breaks and hairline cracks. If any are found, discard food from those jars. If no cracks are found, food may be transferred from jars into freezer bags or containers and stored in the freezer, or it may be kept in the refrigerator for use within a day or two.
Home-canned foods which have been frozen may be less palatable due to texture changes than properly stored canned foods. Do not recan home-canned foods which have been frozen.
How do you protect canned foods against freezing?
Wrap the jars in paper or cover them with blankets. However, if the storage area temperature is expected to be below freezing (32° F) for more than a day or two, move the food to a warmer storage area.
What does mold on canned food indicate?
It means the jar has not sealed and the food is spoiled. Even if mold appears to be only on the surface, discard all food in the container because parts of the mold may not be visible in the food.
Is it safe to can foods without salt?
Yes. Salt is used for flavor only in canned vegetables and is not necessary for safe processing. Since the characteristic flavor and texture of pickled vegetables depend on salt, do not omit this ingredient from recipes for pickles and relishes.
What kind of salt should be used in pickling? Why?
Use pure granulated salt. Uniodized table salt can be used, but materials added to the salt to prevent caking may make the brine cloudy. Do not use iodized table salt because it may darken pickles.
What type of vinegar should be used for making pickles? Can it be diluted?
Use cider or white distilled vinegar of 4% to 6% acidity (40 to 60 grain). Do not use vinegar of unknown acidity. Do not dilute vinegar unless the recipe so specifies. If a less sour product is preferred, add sugar rather than decrease vinegar.
Why should pickles be processed in a boiling-water bath?
Pickles require heat treatment to destroy organisms that cause spoilage, and to inactivate enzymes that may affect flavor, color, and texture.
Heat processing in a boiling-water bath is recommended for all pickle products. There is always danger of spoilage organisms entering the food when it is transferred from kettle to jar. This is true even when the utmost caution is observed and is the reasonopen-kettle canning is not recommended.
Why should plastic containers not be used when brining pickles?
Vegetables being pickled undergo physical as well as chemical changes during brining or fermentation. As a result of these changes, the plastic may be affected, causing undesirable compounds to be formed or leached from the plastic.
For fermenting or brining pickles, use a crock or stone jar, unchipped enamel-lined pan, or large glass jar, bowl, or casserole.
What causes pickles to be hollow?
Hollowness in pickles generally results from poorly developed cucumbers, holding cucumbers too long before pickling, too rapid fermentation, too strong or too weak a brine during fermentation.
What causes jelly to be too soft?
Too much juice in the mixture, too little sugar, mixture not acid enough (overripe fruit), or making too big a batch at one time.
What makes jelly tough?
Mixture was cooked too long to reach jellying stage because too little sugar was used in proportion to the pectin and acid in the juice.
What makes crystals form in jelly?
Crystals throughout the jelly may be caused by too much sugar in the jelly mixture, or cooking the mixture too little, too slowly, or too long. Crystals on top of jelly that has been opened and allowed to stand are due to evaporation of liquid.
Tartrate crystals in grape jelly may occur if juice has not been allowed to stand overnight and then strained through a double thickness of cheesecloth before preparing jelly.
Is a one-door refrigerator-freezer combination suitable for freezing and storage of frozen fruits and vegetables?
It may be difficult to obtain the recommended temperature of 0° F or below for freezing and storing foods in this style freezer without freezing food in the refrigerator part as well.
Recommended storage times are severely reduced if a freezer does not maintain 0° F or below. If freezer temperatures are above 10°, do not store frozen food for more than several weeks.
Can containers for commercial foods, such as cottage cheese, margarine, milk, yogurt, ice cream, or sour cream, be used for freezing fruits and vegetables?
Waxed cardboard cartons which previously contained dairy products are not sufficiently moisture-vapor-resistant to use for packaging foods to be frozen.
Plastic commercial-food containers are suitable if they can be tightly sealed and do not become brittle and crack at low temperatures, thus exposing the food to the air.
Can citric acid or lemon juice be used to help prevent fruit from turning dark during freezer storage?
Although these products can be used as anti-darkening agents, neither is as effective as ascorbic acid. Often the quantity of citric acid or lemon juice needed to prevent darkening is so large that natural flavors are masked or the fruit becomes too sour.
Why is it necessary to wash and blanch vegetables before they are frozen?
Washing removes dirt and some of the bacteria from vegetables. Freezing inhibits the growth of bacteria, but does not kill them. Thus it’s important that the food, as well as all surfaces it touches, be kept clean so that the number of bacteria on the food is held to a minimum. Bacteria can grow on food if the temperature rises during freezer storage, and when food is thawed.
Except for green peppers and mature onions, vegetables must be blanched to destroy enzymes which could cause undesirable changes in flavor, texture, and color during freezer storage.
Why can green peppers and mature onions be frozen without blanching?
Unlike other vegetables, green peppers and onions do not lose quality during freezer storage if their enzymes are not destroyed by blanching before freezing.
Green peppers frozen without heating are better suited for use in uncooked foods than are blanched peppers. Some of the characteristic flavor of onions is lost if this vegetable is blanched before freezing.
Why is corn which is frozen on-the-cob blanched for longer times than cut corn?
Longer blanching of corn frozen on-the-cob is necessary so that enzymes present in the cob will be destroyed. Otherwise, enzymes in the unheated cob can cause undesirable flavor changes in the corn kernels.
Corn frozen off-the-cob needs only to be blanched just enough to destroy enzymes in the kernels.
Can vegetables be blanched by steaming instead of by heating in boiling water?
The following vegetables may be heated in steam: broccoli, mushrooms, pumpkin, winter squash, and sweet-potatoes.
To steam these vegetables, put 1 to 2 inches of water in a large kettle; bring water to a boil. Add a basket containing a single layer of prepared vegetable; keep the basket at least 1 inch above the water. Cover kettle and start timing.
Steam broccoli 3 minutes; sliced mushrooms, 3 minutes; whole mushrooms (less than 1-inch diameter), 5 minutes. Steam pumpkin, winter squash, or sweet-potatoes until tender.
Is it necessary to make an adjustment in blanching times for vegetables at altitudes above sea level?
At altitudes 5,000 feet or more above sea level, heat vegetables 1 minute longer than the time given in directions for the vegetable being blanched.
What can be done to prevent food from thawing if the freezer should stop running?
Never open the freezer unnecessarily. A fully-loaded freezer will usually remain cold enough to keep food frozen for 2 days if the door is not opened; a half-loaded freezer may not stay cold enough more than a day.
If power cannot be restored or the freezer cannot be fixed before the food would start to thaw, use dry ice. If dry ice is obtained shortly after the failure has occurred and the freezer is fully loaded, 25 pounds of dry ice should keep a 10-cubic-foot freezer at temperatures below freezing for 3 to 4 days; if freezer is less than half-full, for 2 to 3 days.
Place dry ice on boards or heavy cardboard on top of the packages of food. Handle dry ice carefully—never with your bare hands. Wear gloves to prevent burns.
Another alternative is to move food to a neighbor’s freezer or to a freezer locker plant where space can be rented.
Can vegetables and fruits which have thawed be refrozen?
Frozen foods that have thawed may be safely refrozen if they still contain ice crystals or if they are still cold—about 40° F—and have been held no longer than 1 or 2 days at refrigerator temperatures (32° to 40°) after thawing.
Since thawing and refreezing reduces the quality of fruits and vegetables, use refrozen foods as soon as possible to save as much of their eating quality as you can.
compiled by Annetta Cook and Carole Davis[21]
Acid food—Food with a pH of 4.6 or below. An acid food can be safely processed in a boiling-water bath for specified times. Includes most fruits, tomatoes, and pickled vegetables.
Anaerobes—Bacteria capable of growing without air, as in a sealed container of canned food.
Blanching—Heating vegetables by immersion in boiling water, steaming, sauteing, or stewing to inactivate enzymes capable of causing quality changes in foods during freezer storage.
Boiling-water-bath Canner—A large kettle with lid, rack, and cover; must be deep enough to allow jars to be covered with 1 to 2 inches of water and still have additional height for water to boil actively. Suitable for processing acid foods.
Botulism—Food-borne illness caused from eating canned foods containing the toxin produced byClostridium botulinum, an anaerobic bacterium. This organism can grow and produce toxin in sealed jars of canned foods that are improperly processed.
Canning—Preserving food in airtight rigid containers. Micro-organisms are destroyed by heat-processing containers of food at the temperature and time specified for each food. It is essential to follow reliable canning instructions exactly to insure a safe canned product that is free from botulism-causing bacteria and spoilage organisms.
Cold Pack—Raw, unheated food packed into canning containers and covered with boiling sirup, juice, or water.
Dehydrator—A device which removes moisture, a dryer.
Enzymes—Proteins involved in plant growth processes including maturation and ripening. Enzymes can cause loss of quality in food if they remain active during storage. They are destroyed by canning, or by blanching vegetables before freezing.
Freezer Burn—Small, white, dehydrated areas which occur on improperly wrapped frozen foods. This condition is harmless, but if extensive can cause food to become tough or lose flavor.
Freezing—Preserving food by storing at low temperatures. The recommended temperature for freezer storage is 0° F or below.
Headspace—The space between the top of food in a container and the container lid or closure.
Hot Pack—Food heated in sirup, water or steam, or juice, and packed hot into canning jars.
Hydrator (Vegetable Crisper)—A drawer-like section in refrigerators which protects fresh fruits and vegetables from drying out during refrigerator storage.
Low-acid Food—Food with pH above 4.6. A low-acid food requires processing at high temperature under pressure to destroy micro-organisms and insure a safe canned product. Includes all vegetables except tomatoes.
Micro-organism—Includes bacteria, molds, and yeasts, which when present in food can cause spoilage and even food poisoning. Therefore, they must be destroyed in canning foods or their growth prevented in freezing and drying foods.
Moisture-vapor-proof—Packing materials that prevent loss of moisture from foods during freezer storage. Examples include glass, rigid plastic, and metal freezer containers.
Moisture-vapor-resistant—Packing materials that protect foods from moisture loss during freezer storage. Examples include freezer wraps—paper, plastic, or foil—plastic bags, waxed freezer cartons.
Molds—Microscopic fungi which form air-borne spores (seeds) that may alight on food and grow into cottony mats or fuzz. Some molds or their end products may be harmful, and moldy vegetables or fruit should not be canned. Molds are destroyed by proper canning, but they may develop in leaky containers. Food from leaky containers or any canned food showing mold growth should be discarded without tasting.
Open-kettle Canning—Procedure whereby food is cooked in an ordinary kettle, then packed into hot jars and sealed. Jars of food receive no additional heat processing. This is a dangerous practice as spoilage organisms may enter the jar during the transfer of food from kettle to jar. In low-acid foods,temperatures obtained are not hot enough to insure destruction of all spoilage organisms that may be present in the food.
Pack—Designates how food is packed into containers. Specifies the temperature of food when packed into jars for canning, or the method of sweetening fruits for freezer packs.
Pectin—A substance occurring naturally in many fruits which causes the juice to thicken or gel after heating if the proper proportions of sugar and acid are present. Natural pectins are more prevalent in underripe fruit than mature or overripe fruit. Some fruits have enough natural pectins to make high quality jams and jellies. Others require addition of commercial pectins which are made from either citrus peel or apples.
pH—Measure of acidity of a product. The lower the pH the higher the acidity.
Preserve—To maintain the quality of food for consumption at a later time. Accomplished by canning, freezing, pickling, drying, or making jelly, jams, or preserves.
Processing—Heating food in closed canning jars to insure destruction of micro-organisms so the canned food will remain unspoiled and safe to eat. Acid foods—such as fruits, tomatoes, and pickles—and jams and preserves are safely processed in a boiling-water-bath. Low-acid vegetables (all vegetables except tomatoes) require processing at higher temperature by use of a pressure canner or pressure saucepan. Times required to insure an adequate process are specified in canning directions for each food.
Sirup Pack—Fruit is packed for freezing in a sugar sirup made by dissolving sugar in water.
Steam-pressure Canner—A large, heavy metal pan having a tight-fitting cover which is fitted with safety valve, steam vent or petcock, and a gage—either weighted or dial. Used for processing low-acid foods under pressure at high temperatures in order to insure their safety.
Steam-pressure Saucepan—Smaller than a canner. If equipped with a gage to maintain pressure at 10 pounds, it is suitable for processing food in pint jars.
Sugar Pack—Sugar is added directly to fruit and mixed gently to draw juice from fruit before packing into freezer containers.
Unsweetened Pack—Fruit packed for freezing without any sweetening added. It may be packed dry or covered with water.
[1]Edmund A. Zottola is Extension Food Microbiologist and Isabel D. Wolf is Extension Specialist, Foods and Nutrition, at the University of Minnesota, St. Paul.[2]Gerald D. Kuhn is Professor, Food Science Extension, and Louise W. Hamilton is Professor, Foods & Nutrition Extension, The Pennsylvania State University, University Park.[3]Ruth N. Klippstein is Professor, Division of Nutritional Sciences, Cornell University, Ithaca, N.Y.[4]Frances Reasonover is Extension Food and Nutrition Specialist, Texas A & M University, College Station.[5]Charlotte M. Dunn is Food and Nutrition Specialist, University of Wisconsin-Extension, Madison.[6]Nadine Fortna Tope is Extension Specialist in Food Conservation and Preparation, North Carolina State University, Raleigh.[7]Carole Davis is a Supervisory Food Technologist, Consumer and Food Economics Institute, Agricultural Research Service.[8]These instructions are for green beans only. Procedures and processing times are specific for each vegetable. See USDA Home and Garden Bulletin No. 8,Home Canning of Fruits and Vegetables, for directions for canning other vegetables.[9]These instructions are for peaches only. Procedures and processing times are specific for each fruit. See USDA Home and Garden Bulletin No. 8,Home Canning of Fruits and Vegetables, for directions for canning other fruits.[10]Annetta Cook is a Food Technologist in the Consumer and Food Economics Institute, Agricultural Research Service.[11]These instructions are for strawberries only.[12]These instructions are for green peas only. Preparation procedures and blanching times are specific for each vegetable. See USDA Home and Garden Bulletin 10,Home Freezing of Fruits and Vegetables, for directions for freezing other vegetables.[13]Catherine C. Sigman is Extension Home Economist—Foods, University of Georgia, Athens. Kirby Hayes is Professor, Department of Food Science and Nutrition, University of Massachusetts, Amherst.[14]Isabelle Downey is Home Economist-Food Preservation, Cooperative Extension Service, Auburn University, Auburn, Ala.[15]Philip Wagner is Proprietor, Boordy Vineyards, Riderwood, Md., and author ofGrapes Into Wine. J. R. McGrew is with the Agricultural Research Service, Beltsville, Md.[16]Dale E. Kirk is a Professor and Agricultural Engineer at Oregon State University, Corvallis. Carolyn A. Raab is Extension Foods and Nutrition Specialist at Oregon State.[17]Ralph W. Johnston is Chief, Microbiology Staff, Meat and Poultry Inspection Program, Food Safety and Quality Service.[18]Anton S. Horn is Extension Horticulturist, University of Idaho, Boise. Esther H. Wilson is Extension Nutrition Specialist, University of Idaho, Moscow.[19]F. Aline Coffey is Foods and Nutrition Specialist, Vermont Extension Service, University of Vermont, Burlington. Roger Sternberg is Project Coordinator, Bread and Law Taskforce, Montpelier, Vt.[20]Carole Davis and Annetta Cook are Food Technologists with the Consumer and Food Economics Institute, Agricultural Research Service.[21]Annetta Cook and Carole Davis are Food Technologists with the Consumer and Food Economics Institute, Agricultural Research Service.
[1]Edmund A. Zottola is Extension Food Microbiologist and Isabel D. Wolf is Extension Specialist, Foods and Nutrition, at the University of Minnesota, St. Paul.
[2]Gerald D. Kuhn is Professor, Food Science Extension, and Louise W. Hamilton is Professor, Foods & Nutrition Extension, The Pennsylvania State University, University Park.
[3]Ruth N. Klippstein is Professor, Division of Nutritional Sciences, Cornell University, Ithaca, N.Y.
[4]Frances Reasonover is Extension Food and Nutrition Specialist, Texas A & M University, College Station.
[5]Charlotte M. Dunn is Food and Nutrition Specialist, University of Wisconsin-Extension, Madison.
[6]Nadine Fortna Tope is Extension Specialist in Food Conservation and Preparation, North Carolina State University, Raleigh.
[7]Carole Davis is a Supervisory Food Technologist, Consumer and Food Economics Institute, Agricultural Research Service.
[8]These instructions are for green beans only. Procedures and processing times are specific for each vegetable. See USDA Home and Garden Bulletin No. 8,Home Canning of Fruits and Vegetables, for directions for canning other vegetables.
[9]These instructions are for peaches only. Procedures and processing times are specific for each fruit. See USDA Home and Garden Bulletin No. 8,Home Canning of Fruits and Vegetables, for directions for canning other fruits.
[10]Annetta Cook is a Food Technologist in the Consumer and Food Economics Institute, Agricultural Research Service.
[11]These instructions are for strawberries only.
[12]These instructions are for green peas only. Preparation procedures and blanching times are specific for each vegetable. See USDA Home and Garden Bulletin 10,Home Freezing of Fruits and Vegetables, for directions for freezing other vegetables.
[13]Catherine C. Sigman is Extension Home Economist—Foods, University of Georgia, Athens. Kirby Hayes is Professor, Department of Food Science and Nutrition, University of Massachusetts, Amherst.
[14]Isabelle Downey is Home Economist-Food Preservation, Cooperative Extension Service, Auburn University, Auburn, Ala.
[15]Philip Wagner is Proprietor, Boordy Vineyards, Riderwood, Md., and author ofGrapes Into Wine. J. R. McGrew is with the Agricultural Research Service, Beltsville, Md.
[16]Dale E. Kirk is a Professor and Agricultural Engineer at Oregon State University, Corvallis. Carolyn A. Raab is Extension Foods and Nutrition Specialist at Oregon State.
[17]Ralph W. Johnston is Chief, Microbiology Staff, Meat and Poultry Inspection Program, Food Safety and Quality Service.
[18]Anton S. Horn is Extension Horticulturist, University of Idaho, Boise. Esther H. Wilson is Extension Nutrition Specialist, University of Idaho, Moscow.
[19]F. Aline Coffey is Foods and Nutrition Specialist, Vermont Extension Service, University of Vermont, Burlington. Roger Sternberg is Project Coordinator, Bread and Law Taskforce, Montpelier, Vt.
[20]Carole Davis and Annetta Cook are Food Technologists with the Consumer and Food Economics Institute, Agricultural Research Service.
[21]Annetta Cook and Carole Davis are Food Technologists with the Consumer and Food Economics Institute, Agricultural Research Service.
U.S. GOVERNMENT PRINTING OFFICE: 1978 O-278-050