- Can food be re-canned if the lid does not seal?
Canned food can safely be re-canned if the unsealed jar is discovered
within 24 hours. To re-can, remove the lid and check the jar sealing
surface for tiny nicks. Change the jar if necessary add a new treated
lid and reprocess using the same processing time.
- If canned foods have been frozen during storage, are they safe to
Freezing does not cause food spoilage unless the seal is damaged or
the jar is broken. This often happens as the food expands during
freezing. However, frozen foods may be less palatable than properly
stored canned food. In an unheated storage place, protect canned foods
by wrapping the jars in paper or covering them with a blanket.
- If my recipe doesn't call for processing, do I need to do so?
Many recipes passed down through the years or found in older cookbooks
do not include instructions for processing. The foods are usually
canned by the open kettle method, sealed and stored. Foods prepared in
this manner present a serious health risk-particularly low acid foods.
To minimize the risk of food spoilage, all high acid foods should be
processed in a water bath canner or pressure canner and all low acid
foods in a pressure canner.
- Do I really need to leave a certain amount of head space in the
Yes, leaving the specified amount of head space in a jar is important
to assure a vacuum seal. If too little head space is allowed the food
may expand and bubble out when air is being forced out from under the
lid during processing. The bubbling food may leave a deposit on the
rim of the jar or the seal of the lid and prevent the jar from sealing
properly If too much head space is allowed, the food at the top is
likely to discolor. Also, the jar may not seal properly because there
will not be enough processing time to drive all the air out of the
- How long will canned food keep?
Properly canned food stored in a cool, dry place will retain optimum
eating quality for at least 1 year. Canned food stored in a warm place
near hot pipes, a range, a furnace, or in indirect sunlight may lose
some of its eating quality in a few weeks or months, depending on the
temperature. Dampness may corrode cans or metal lids and cause leakage
so the food will spoil.
- Is it necessary to sterilize jars before canning?
Jars do not need to be sterilized before canning if they will be
filled with food and processed in a boiling water bath canner for 10
minutes or more or if they will be processed in a pressure canner.
Jars that will be processed in a boiling water bath canner for less
than 10 minutes need to be sterilized by boiling them in hot water for
10 minutes before they're filled.
- Is it safe to process food in the oven?
No. This can be dangerous because the temperature will vary according
to the accuracy of oven regulators and circulation of heat. Dry heat
is very slow in penetrating into jars of food. Also, jars explode
easily in the oven.
- Can two layers of jars be processed in a canner at one time?
Yes, two layers can be processed at one time, in either the boiling
water bath or pressure canner. Place a small wire rack between the
layers so water or steam will circulate around each jar. Make certain
that the water covers the top of the jars by 1 inch in a boiling water
bath canner. The pressure canner should have 2 to 3 inches of water in
- Is it necessary to exhaust a pressure canner?
Yes, it is very important to allow steam to escape for 10 minutes
before closing the valve, or placing the weight on the vent. If the
canner is not exhausted, the inside temperature may not correspond to
the pressure on the gauge.
- Should liquid lost during processing be replaced?
No. Loss of liquid does not cause food to spoil, though the food above
the liquid may darken.
- Is it all right to reuse jar fittings (lids and bands)?
Lids should not be used a second time since the sealing compound
becomes indented by the first use, preventing another airtight seal.
Screw bands may be reused unless they are badly rusted or the top edge
is pried up which would prevent a proper seal.
- Why is open kettle canning not recommended?
In open kettle canning, food is cooked in an ordinary kettle, then
packed into hot jars and sealed without processing. The temperatures
obtained in open kettle canning are not high enough to destroy all
spoilage and food poisoning organisms that may be in the food. Also,
microorganisms can enter the food when it is transferred from the
kettle to jar and cause spoilage.
- Why do the 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.
- What causes jars to break in a canner?
Breakage can occur for several reasons: 1. Using commercial food jars
rather than jars manufactured for home canning, 2. Using jars that
have hairline cracks, 3. Putting jars directly on bottom of canner
instead of on a rack, 4. Putting hot food in cold jars, or 5. Putting
jars of raw or unheated food directly into boiling water in the
canner, rather than into hot water (sudden change in temperature-too
wide a margin between temperature of filled jars and water in canner
- If I find mold growing inside a jar of canned food, can I just
scrape it off and eat the food?
Mold growth in foods can alter the pH of the food. In home canned
products, this could mean that the high acid products could become low
acid and therefore run the risk of botulism or other bacterial
spoilage. Thus, any home canned product that shows signs of mold
growth should be discarded. The exception to this is jellied products.
In these the high sugar content would prevent the growth of Clostridium
botulinum. In jellied products, remove any surface mold plus ½
inch of the good product underneath and then use the rest immediately.
Jellied products with extensive mold should be discarded.
- How can I remove scale or hard-water film from canning jars?
Soak jars for several hours in a solution containing 1 cup of vinegar
and 1 gallon of water.
Vegetables and Fruits
- Is it safe to can food without salt?
Yes. Salt is used for flavor only and is not necessary to prevent
- Is it safe to can fruits without sugar?
Yes. Sugar is added to improve flavor, help stabilize color, and
retain the shape of the fruit. It is not added as a preservative.
- Can fruits and vegetables be canned without heating if aspirin is
No. Aspirin should not be used in canning. It cannot be relied on to
prevent spoilage or to give satisfactory products. Adequate heat
treatment is the only safe procedure.
- Is it safe to can green beans in a boiling water bath if vinegar
No. Recommended processing methods must be used to assure safety.
Recommended processing times cannot be shortened if vinegar is used in
canning fresh vegetables (this does not refer to pickled vegetables).
- Should all vegetables be precooked before canning?
For best quality, yes. However, some vegetables can be packed raw or
cold into jars before being processed in the pressure canner.
- What vegetables expand instead of shrink during processing?
Corn, peas and lima beans are starchy and expand during processing.
They should be packed loosely.
- What causes corn to turn brown during processing?
This occurs most often when too high a temperature is used causing
caramelization of the sugar in the corn. It may also be caused by some
minerals in the water used in canning.
- Should giblets of chicken be canned in the same jar with chicken?
No. Their flavor may permeate other pieces of chicken in the jar.
- Is it safe to can meat and poultry without salt?
Yes. Salt is used for flavor only and is not necessary for safe
- Why is it necessary to remove as much fat from meats as possible
Any fat that gets on the rim of the canning jar can prevent an
airtight seal. Excess fat in jars makes it easier for the fat to climb
the sides of the jar and contaminate the seal.