The Principles of Canning and How to Can Your Food At Home.

  • The purpose of canning is to destroy the causes of food spoilage. Food is made to spoil by tiny organisms called molds, yeasts, and bacteria.
  • It may also spoil because of enzymes.
  • The canner must understand how these spoilers work in order to can food properly.

Enzymes, Yeasts, and Molds.

  • Enzymes are organic substances in food that cause it to ferment. They may be destroyed by heating.
  • Molds usually begin to grow on top of food and spread through the entire food mass.
  • The presence of yeast causes food to ferment, It breaks down sugar and produces a gas and alcohol.
  • Molds and yeasts can be killed by heat, but they may again get into food that is in a poorly sealed can, or which has been canned with unsterilized equipment.


  • There are four kinds of bacteria spoilage:
  • Fermentation turns food sour. It can be recognized by the forming of gas bubbles and acid.
  • Gas often causes jar lids or tin cans to bulge; Liquid will spurt suddenly out of cans of fermented food when they are opened.
  • Fermentation can best be prevented by thorough heating.

Flat Sour

  • Flat Sour is caused by bacteria that come from the soil.
  • It gives the food a sour, unpleasant taste.
  • Non-acid vegetables are principally affected.
  • The food may be soft in appearance and have a cloudy liquid.
  • It may have no odor until it is heated.
  • Flat sour may be prevented by canning the food while it is still fresh, by handling only one cooking at a time, and by rapidly bringing the food to the proper cooking temperature.
  • Jars should be cooled quickly after heating, and stored in a cool place.


  • Putrefaction gives food a bad odor and sometimes causes it to turn dark.
  • It is found in meats and non-acid vegetables and is usually caused by canning food that is not fresh, or by unsanitary handling of the food during canning.

Poisons called toxins

  • Poisons called toxins are not always noticeable unless other forms of spoilage also occur.
  • Meat or nonacid vegetables may have an unpleasant odor after they have been heated.
  • One of the most dangerous food toxins is botulinus, which is likely to occur in nonacid vegetables, especially in beans.
  • The presence of toxins in food may result from careless handling of food during canning, not enough washing of food, or keeping food too long before canning it.
  • Toxins can be prevented by thorough cleaning and clean handling through the canning process.
  • Nonacid vegetables and meat should be precooked, packed loosely in jars, and canned in a pressure cooker.
  • All meats and nonacid vegetables should be boiled for ten to fifteen minutes without tasting after a can has been opened.
  • Foods canned for display purposes at fairs and exhibits are often handled too much during the canning process, causing flat sour to set in.

How to can your food at home.

Handling the Food.

  • Successful home canning depends on the selection of fresh food in perfect condition.
  • Over-ripe or damaged foods should not be canned.
  • Speed in canning is the best policy.
  • Two hours from the garden to the can, ensures maximum food value and minimum spoilage.
  • Food should be spread out and stored in a cool place if it must be kept longer.
  • Absolute cleanliness is essential.
  • Foods should be washed several times until all soil and grit are removed.
  • All blemishes, tough peels, and hulls should be completely removed.
  • Tomatoes and peaches may be dipped in boiling water until the skins loosen, then put in cold water to make them easier to handle.
  • Large seeds may be removed.
  • All green or white parts should be taken of tomatoes.
  • Food should be sorted and graded according to size and stage of ripeness.
  • All foods, except perhaps tomatoes, should be precooked for a short time before they are packed in the hot sanitary jars.
  • This saves color and vitamins and improves the flavor.
  • It also shrinks the food so that more will go in one jar.
  • And it brings food to the proper processing temperature more quickly.
  • Thus, flat sour does not develop.
  • Meat for canning should be thoroughly chilled after slaughtering, but should not be frozen.
  • It should be wiped clean with a damp cloth.
  • Large bones, gristles, and most of the fat should be removed.
  • Meat should be precooked in an oven or water if it is to be canned in glass jars.
  • If tin cans are used, meat may be packed in them cold and then precooked in the can before sealing.
  • Enameled cans should not be used in canning meat, for the fat causes enamel to peel.
  • Meats should not be fried before canning.
  • The brown crust becomes dry and hard, and the meat may have a disagreeable taste.

Preparing the Food.

  • There are two methods of preparing foods for canning, cold packing and hot packing.

Cold packing is the older method.

  • Foods are packed raw or are scalded or blanched, and then dipped in cold water.
  • This method is less satisfactory because longer cooking of the food in the jar is required to destroy bacteria or botulinus.
  • This method is no longer recommended, not only because of the above reason but because the food shrinks in the jar, causing much waste space.

In hot packing;

  • Foods are precooked to kill bacteria before being put into jars or cans. Canning charts tell how long each food should be cooked.
  • The food should be put into jars and sealed as soon as the precooking is completed.
  • The boiling water in which vegetables have been cooked is added to the jars for liquid.
  • One teaspoon of salt should also be put into each quart jar of vegetables.
  • Most fruits are canned in sirup, but they may be canned in their own juice without syrup.
  • There are three standard recipes for fruit syrups.
  • A thin sirup of three parts water or fruit juice to one part sugar is used for soft fruits, such as sweet cherries and berries.
  • A medium sirup of two parts water or fruit juice to one part sugar is used on sour berries, peaches, and acid fruits.
  • A heavy sirup of one part water and one part sugar is used on sour fruits that are to be very sweet.

Filling the Jars.

  • Containers should be filled quickly to keep the precooked food hot.
  • If a rubber ring is used it should be placed on the jar before filling, to prevent danger from burn.
  • A funnel is a great aid in filling jars.
  • After the jar is filled, the rubber ring and the sealing edge of the jar should be carefully wiped clean, and the
  • cap adjusted.
  • The lid on a screw-top jar should be tightened completely, then loosened one-half turn.
  • The band on the vacuum-seal lids should be tightened completely.
  • The bail on the lightning jars should be put in place, but the small wire clamp should be left up.
  • The cooking or processing should be done as soon as the jars or cans are sealed.

Final Processing.

  • There are several methods of heating in the final stage of the canning process.
  • The steam pressure cooker is best for all nonacid foods, such as beans, peas, corn, asparagus, greens, carrots, and all meats.
  • The boiling-water bath is recommended for acidic vegetables and fruits.
  • The open-kettle method is used principally for making preserves and jellies.
  • Most canners have found oven canning dangerous and unreliable.
  • The steam canner works on the same principle as oven canning, except that it uses a shallow water pan beneath the racks.
  • This pan is heated until the water is turned into steam.
  • Care must be taken to keep enough water to produce steam at all times.
  • Steam canning is not as satisfactory as the water bath.

The Pressure Cooker.

  • The steam pressure cooker is an extra heavy kettle with a lid held tightly with clamps or other devices.
  • Steam is kept from escaping, and as it increases the pressure, temperatures above boiling are reached in the kettle.
  • A gauge on the lid shows the number of pounds of pressure, indicating the temperature inside.
  • A petcock provides an outlet for steam and air.
  • There is also a safety valve.
  • Several precautions should be followed in using a pressure cooker.
  • Jars should be placed on the rack so that they do not touch one another.
  • The lid should be adjusted carefully and fastened tightly so that no steam can escape through the petcock.
  • The petcock should stay open until steam has poured out steadily for ten minutes or more.
  • Then it should be closed to allow the pressure to rise to the correct level, which is ten pounds for most foods.
  • When the right pressure has been reached, the heat should be adjusted to keep the same pressure without variation.
  • When the processing time is over, the cooker should be taken off the heat and left alone until the pressure goes down to zero.
  • Then the petcock should be opened to release the remaining steam.
  • Liquid may be lost from the jars if the pressure varies during processing, or if the steam is released too quickly.
  • Jars should not be reopened and refilled with liquid under any circumstances.
  • The cooker may be opened when most of the steam is out.
  • Tilt up the far side of the lid to avoid burns.
  • The cooker should not sit for a long time unopened after the steam is down.
  • A vacuum may develop which will make it difficult to open the lid.
  • Reheat the cooker for a few minutes.
  • The jars are next taken out of the cooker, and their lids or bails tightened if necessary.
  • The jars should be placed on a rack or towel in a cool place out of the draft.
  • The cooker should be cleaned carefully, but the lid should not be placed in water.
  • It should be stored clean in a place where it can be aired.

   The Boiling-Water Bath

  • It requires a container deep enough that it can hold water to cover the tops of the jars to a depth of at least two inches.
  • The containers should have a mesh or slat rack in the bottom on which to set the jars.
  • It must have a tight-fitting lid.
  • A wash boiler or any deep kettle can be used, and special canning kettles are available.
  • The water in the canner must be boiling when the jars are placed in it and must be kept at a “rolling boil at all times.
  • The water will stop boiling when the jars are first lowered into it, so processing time should not be counted until boiling begins again.
  • The jars should be kept far enough apart to let the water surround each jar.
  • Tongs can be used for removing the jars safely from the water bath.
  • The seal should be completed and the jars cooled after pressure cooker canning.
  • In the open kettle method of canning, the food is completely cooked on the stove.
  • Then it is packed hot into sterilized containers and sealed at once.

Handling After Canning.

  • The metal bands may be taken off the two-piece lids after the jars have cooled for twenty-four hours.
  • The jars should be wiped clean and labeled with the name of the food and the date of canning.
  • They should be stored in a cool. a dry, dark place.
  • The jars should be examined ten days after canning for signs of spoilage.
  • All spoiled food should be thrown away at once.
  • It is wise to boil in soda water the lids of jars in which food has spoiled before they are used again.

Things to note:

  • certain bad canning results can be avoided by taking the necessary precautions.
  • Sometimes the liquid on peas and beans turns cloudy.
  • Cloudiness can be avoided by using vegetables that are not overripe.
  • Cloudiness may also result if the water used in canning is too hard.
  • White sediment in canned beets may result from using very hard water, or from packing the beets too tightly
  • in the jar.
  • Separation of water and pulp in tomato juice may come from overcooking the tomatoes before pressing out the juice, or from using too coarse a sieve in straining the juice.
  • Fruit can be kept from floating on top of the can by precooking it for a short time.
  • This allows the fruit to shrink before it is put in the jars.
  • Crystals in grape juice are a natural formation, and cannot be prevented.
  • The sulfur in certain foods will discolor metal lids and this is not harmful.


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