A Guide for Canning Vegetables

A Canned vegetables
As all we known that all agricultural products is perishable. This perishable characteristic is all because of a high water content level consisting in them. This condition happened to vegetables as one of agricultural products that need time to reach to the consumers. 

Therefore, it's need a technique to preserve vegetables to not defect when it's ready to be consump by the consumers. One of the preservation techniques that reliable for vegetables is canning.

All vegetables, except tomatoes, require processing in a pressure canner with a weighted control or dial gauge. Because tomatoes are more acidic, they can be safely processed in a boiling water bath.

Food Safety Concerns

A deadly form of food poisoning, botulism, can occur when low-acid foods are improperly processed. The higher temperatures of the pressure canner are necessary to ensure that any Clostridium botulinum spores are killed. If the organism is present in canned low-acid vegetables, botulism toxin can be produced. Even sealed containers without any visible sign of spoilage can contain botulism toxin.
  • To avoid the risk of botulism, make sure your pressure canner is in good working order; check the gauge yearly for accuracy; follow all canning recommendations exactly.
  • Since the rate of heat penetration and acidity is affected by the combination of foods used, do not can vegetable mixtures such as vegetable soup or chili sauce unless you have a laboratory tested recipe.
  • Never thicken vegetables prior to canning. For mixed vegetables look up the processing time for each vegetable in the mixture. Use the processing time for the vegetable that requires the longest processing time.
  • Always check home canned vegetables carefully for signs of spoilage before and after opening. When opening, watch for spurting liquid, an off odor, or mold.

If there is any doubt in your mind whether home canned food food is spoiled, don’t use it. Burn any spoiled food or dispose of it so that it will not be eaten by humans or animals. Also, be sure to boil low-acid vegetables for 10 minutes before tasting or serving.

Select and prepare vegetables carefully
  • Choose only fresh, young, tender vegetables. Wash thoroughly, small amounts at a time, under running water or through several changes of water. Lift the vegetables gently out of the water so dirt washed off will not settle back on the food. Rinse the pan or sink between washings.
  • The number of quarts of canned food from a given amount of fresh vegetables depends on quality, condition, maturity, and variety of the vegetable; the size of pieces packed; and the way the vegetable is packed-raw or hot pack.
  • Generally, the following amounts of fresh vegetables (as purchased or picked) make 1 quart when canned:
    • Asparagus: 2 to 4 pounds
    • Beans, lima, in pods: 3 to 5 pounds
    • Beans, snap or green: 1 to 3 pounds
    • Beets, without tops: 2 to 3 pounds
    • Carrots, without tops: 2 to 3 pounds
    • Corn, sweet, in husks: 3 to 6 pounds
    • Peas, green, in pods: 3 to 6 pounds 
    • Pumpkin or winter squash: 1 to 3 pounds
    • Spinach and other greens: 2 to 6 pounds 

Use standard jars and lids
  • Use only jars and two-piece lids made especially for canning. Check jars and lids for cracks, chips, dents and rust; these defects cause sealing failures. Commercial jars such as those for mayonnaise are not recommended for home canning because they are not designed for use with two-piece lids and because the glass is more likely to break during processing. Wash jars in hot, soapy water; rinse well. Prepare lids and bands according to manufacturer’s directions.
  • Mineral deposits or hard water film on jars can be removed by soaking the empty jars for several hours in a solution of 1 cup vinegar per gallon of water. To avoid mineral deposits on jars during processing add 1⁄4 cup vinegar per gallon of water used in the pressure canner.

Fill jars and adjust lids
  • Vegetables can be packed raw, or preheated and packed hot. See Table 1 (released in next posting) for specific directions.
  • Most raw vegetables should be packed closely because they shrink during processing. Corn, lima beans and peas absorb liquid and expand when processed so should be loosely packed. To ensure proper heat penetration, do not pack vegetables too tightly. Vegetables packed hot should be at or near boiling temperature and should be packed loosely.
  • Use the hot cooking liquid and add boiling water, if needed, to fill the jar and cover the food for both raw and hot packed vegetables. If the vegetables at the top of the jar are not covered they may darken.
  • Salt is not needed for preservation in canned products but can be added for flavor. Use 1 teaspoon per quart or 1⁄2 teaspoon per pint.
  • The space between the packed food and liquid and the top of jar is called headspace. The amount of headspace required is given with details for canning each vegetable. Too much or too little headspace will affect jar seals.
  • Slide a non-metallic spatula between food and side of jar to remove any air bubbles. Wipe jar rims to remove food particles that might interfere with sealing. Adjust lids.

Check altitude
  • As altitude increases, water boils at a lower temperature (below 212° F). Lower temperatures are not as effective for destroying organisms. Therefore, when using a pressure canner, the pressure must be increased as altitude increases.

Process in a pressure canner
  • Partially fill canner with 2 to 3 inches of water. Place jar rack and sealed jars in canner. Fasten lid. Heat on high. After steam exhausts for 10 minutes, add weighted gauge or close petcock. Allow canner to reach designated pressure. Start timing when designated pressure is reached. Regulate heat to maintain a constant pressure.
  • Process for the time recommended in Table 2 (released in next posting). Do not reduce the processing time.
  • When processing is complete, remove canner from the burner.
  • Allow the canner to cool at room temperature until it is fully depressurized.
  • This will take 30 to 60 minutes depending on the type of canner. Do not rush the cooling by setting the canner in water or by running cold water over the canner.
  • Do not open the vent or lift the weight to quicken the reduction of pressure.
  • When the pressure has dropped to zero, carefully open the petcock or remove the weighted gauge. Wait 2 minutes, then slowly release and remove the canner lid.

Remove and store jars
  • Take jars from canner and set upright on a rack or folded cloth away from drafts. Do not tighten the screw bands.
  • Allow jars to cool undisturbed for 12 to 24 hours, then check for sealing failures. 
  • To test jar, press center of lid. If lid is down and will not move, jar is sealed. Remove screw bands carefully. 
  • Wash, dry, label, and store jars in a cool, dark place. If any jars have not sealed, place in refrigerator and use within two days. Vegetables can be reprocessed with fresh liquid, new lids and clean jars, and the full processing time, but quality will be affected.

  • Textbook of Food Science and Technology

    Next Post: Guidance for Preparing and Packing Vegetables

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