Quality for Keeps: Steps to Success in Home Canning
Barbara J. Willenberg
Department of Food Science and Human Nutrition,
Your home-canned products will be only as good as the fresh foods you start
with. For high-quality, safe, home-canned foods, select the freshest foods possible.
Discard diseased and moldy foods. Don't can foods that you wouldn't serve at
your table fresh.
Fruits and vegetables are at peak quality for six to 12 hours after being
picked. For this reason, produce picked from your garden or purchased from "you
pick" stands or nearby farmers' markets is usually good for canning.
Allow apricots, peaches, pears and plums to ripen one or more days between
harvest and canning for best results. If you must delay the canning of other
fresh produce, keep it refrigerated until you are ready to can.
Chill and can fresh, home-slaughtered red meats and poultry without delay.
Do not can meat from diseased animals. Immediately after catching fish, remove
guts, put on ice, and can within two days.
Keep your canned foods looking and tasting
fresh
To make sure your canned foods keep the best possible color and flavor during
processing and storage:
- Use only high-quality foods at their proper maturity, free from diseases
and bruises.
- Use the hot-pack method, especially for acid foods to be processed in a
boiling-water canner.
- Prevent darkening of fruits by holding them in an ascorbic acid (vitamin
C) solution.
- Fill jars while food is still hot, and use the correct headspace specified
in recipes.
- Tighten screw bands securely, but not as tightly as possible. Process and
cool jars.
- Store the jars in a cool, dark place (50 degrees Fahrenheit to 70 degrees Fahrenheit).
- Can no more food than you will use within a year.
A fresh look is easy
Ascorbic acid helps prevent the discoloration of apples, apricots, peaches,
pears, mushrooms and potatoes, and stem-end darkening of cherries and grapes.
You can find ascorbic acid in several forms.
- Pure powdered ascorbic acid is available among canners' supplies in supermarkets
during the canning season. One level teaspoon of pure powder weighs about three
grams. Use one teaspoon per gallon of water as a treatment solution.
- Vitamin C tablets are economical and available year-round in many stores.
Crush and dissolve six 500-milligram tablets in a gallon of water as a treatment
solution.
- Commercially prepared mixtures of ascorbic and citric acid are available
among canners' supplies in supermarkets. Follow the manufacturer's directions.
Citric acid powder is often sold in supermarkets, but it is less effective
in controlling darkening.
Hot-pack for canned foods that sizzle with
taste
Home-canned food retains quality longer when air is removed from the food
before jars are sealed. Hotpacking is the best way to remove air. It also "shrinks" food
so that more will fit into each jar, helps keep the food from floating, increases
vacuum in sealed jars and improves shelf life.
How to hot-pack
- Bring freshly prepared food to a boil and simmer two to five minutes. Loosely
fill jars with the boiled food.
- Hot-packing is the preferred pack style for foods processed in a boiling-water
canner. At first, the color of hot-packed foods may appear no better than that
of raw-packed foods, but within a short storage period, both color and flavor
of hot-packed foods will be superior.
- In raw-packing, jars are filled tightly with freshly prepared, unheated
food. Some foods, especially fruit, will float in the jars. The trapped air
may cause the fruit to discolor in as little as two to three months. Raw-packing
is more suitable for vegetables processed in a pressure canner.
- Whether food has been hot-packed or raw-packed, you should heat the juice,
syrup or water added to the foods to boiling before adding it to the jars.
Figure
1
Headspace allows food to expand and forms a vacuum as jars cool.
Headspace gives food room to breathe
The unfilled space in a jar between the food and the lid is called headspace.
Leave one-fourth inch for jams and jellies, one-half inch for fruits and tomatoes
to be processed in a boiling-water canner and from one inch to 1-1/4 inches
in low-acid foods to be processed in a pressure canner. Headspace allows food
to expand during processing and forms a vacuum as jars cool.
Figure
Mason jar with two-piece lid including a ring band and a metal flat
with sealing compound.
Use the right jars and lids
Regular and wide-mouth, Mason-type, threaded jars with self-sealing lids are
the best choice for home canning. They are available in one-half pint, pint,
1-1/2 pint, quart, and one-half gallon sizes. The regular jar mouth opening
is about 2-3/8 inches. Wide-mouth jars have openings of about 3 inches, which
makes them easier to fill and empty. Use half-gallon jars only for canning very
acid juices. Jelly jars are available in eight-ounce and 12-ounce sizes.
With careful handling, Mason jars and screw bands may be reused many times.
You will need to use new lids (flats) each time, however. After jars have cooled,
remove screw bands. Wash and dry bands and store in a dry area. If left on stored
jars, they become hard to remove and often rust, which makes them unsuitable
for further use.
When you use jars and lids properly, the results are excellent seals and
vacuums and little or no jar breakage.
You can use most commercial pint- and quart-size mayonnaise or salad dressing
jars with new two-piece lids for canning acid foods in boiling-water canners.
However, you should expect more seal failures and jar breakage. Don't use
commercial jars in pressure canners -- excessive breakage is a problem.
Commercial jars with mouths that cannot be sealed with two- piece canning lids
are not recommended for use in canning any food at home.
Show off canned foods with sparkling jars
Before every use, wash empty jars in hot water and detergent and rinse well
by hand. Or, wash in a dishwasher. Unrinsed detergent may cause unnatural flavors
and colors in home-canned food. Remove scale or hard-water film on jars by soaking
jars several hours in a solution containing one cup of vinegar (5 percent acidity)
per gallon of water. These washing methods do not sterilize jars.
Sterilizing jars
Sterilize jars to be used for jams, jellies and pickled products processed
less than 10 minutes. Place empty jars right-side-up on the rack in a boiling-water
canner. Fill the canner and jars with hot (not boiling) water to one inch above
the tops of the jars. Boil 10 minutes at altitudes of less than 1,000 feet.
If you live above 1,000 feet, boil for 11 minutes. Remove hot, sterilized jars
one at a time and drain. Save the hot water for processing filled jars. Fill
jars with food, adjust lids and process as directed.
Jars used for vegetables, meats and fruits to be processed in a pressure
canner do not need to be sterilized. It is also unnecessary to sterilize jars
for fruits, tomatoes and pickled or fermented foods that will be processed 10
minutes or longer in a boiling water canner.
Top it off with the right lid
The two-piece, self-sealing lid is recommended for home canning. It consists
of a flat, metal lid held in place during processing by a metal screw band.
The flat lid is crimped around the bottom edge to form a trough, which is filled
with a colored gasket compound. When jars are processed, the lid gasket softens
and flows slightly to cover the jar-sealing surface, yet allows air to escape
from the jar. The gasket then forms an airtight seal as the jar cools. Gaskets
in unused lids work well for at least five years from date of manufacture if
stored in a cool, dry area. Older unused lids or improperly stored lids may
fail to seal.
Buy only the quantity of lids you will use in a year. To ensure a good seal,
carefully follow the manufacturer's
directions in preparing lids for use. Examine all metal lids carefully. Do not use old, dented
or deformed lids, or lids with gaps or other defects in the sealing gasket.
After filling jars with food, release air bubbles by inserting a flat, plastic
spatula between the food and the jar. (Don't use a metal spatula or knife.)
Slowly turn the jar and move the spatula up and down to allow air bubbles to
escape. Adjust the headspace and clean the jar rim (sealing surface) with a
clean, damp paper towel.
Place the lid, gasket down, onto the cleaned jar rim. Uncleaned jar-sealing
surfaces may cause seal failures. Then fit the metal screw band over the flat
lid. Follow the lid manufacturer's guidelines for tightening the jar lids properly.
Do not retighten lids after processing jars. As jars cool, the contents in
the jar contract, pulling the self-sealing lid firmly against the jar to form
a high vacuum. If screw bands are too loose, liquid may escape from jars during
processing, and seals may fail. If screw bands are too tight, air cannot vent
during processing, and food will discolor during storage. Overtightening may
also cause lids to buckle and jars to break, especially with raw-packed, pressure-processed
food.
Canners put the pressure on
There are two main types of canners for home canning: boiling-water canners
and pressure canners. Most hold seven quart jars or eight to nine pint jars.
Small pressure canners hold four quart jars; some large pressure canners hold
18 pint jars in two layers, but only seven quart jars. Never use pressure saucepans
with smaller-volume capacities for canning.
You must process low-acid foods, like vegetables, meat, poultry and fish,
in a pressure canner to prevent botulism, an often fatal type of foodborne illness.
Although pressure canners may also be used for processing some acid foods, such
as fruits, boiling water canners are recommended for this purpose because they
are faster.
Boiling-water canners
Boiling-water canners are made of aluminum or porcelain-covered steel. They
have removable, perforated racks and fitted lids. The canner must be deep enough
so that at least one inch of briskly boiling water will cover the tops of jars
during processing. Boiling-water canners with ridged bottoms can be used only
on a gas range. Boiling-water canners with flat bottoms can be used on either
a gas or electric range. To ensure uniform processing of all jars with an electric
range, the canner should be no more than four inches wider than the burner (meaning
that when centered over the burner, the canner would overhang the burner by
two inches all the way around).
Boiling-water canning step-by-step
- Fill the canner halfway with water.
- Preheat water to 140 degrees Fahrenheit for raw-packed foods and to 180 degrees Fahrenheit for hot-packed foods.
- Load filled jars, fitted with lids, into the canner rack and use the handles
to lower the rack into the water; or fill the canner, one jar at a time, with
a jar lifter.
- Add more boiling water, if needed, so the water level is at least one inch
above jar tops. Do not pour directly on jar tops.
- Turn heat to its highest position until water boils vigorously.
- Set a timer for the minutes required for processing the food. Be sure to
use correct time for your altitude.
- Cover the canner and lower the heat setting to maintain a gentle boil throughout
the process schedule.
- Add more boiling water, if needed, to keep the water level at least one
inch above the jars.
- When jars have been processed for the recommended time, turn off the heat
and remove the canner lid. Wait five minutes before removing the jars
- Use a jar lifter to remove the jars, and place them on a towel. Leave at
least one inch of space between the jars during cooling.
Figure 3
Dial-gauge canner
Figure 4
Weighted-gauge canner
Pressure canners
Pressure canners for use in the home have been extensively redesigned in recent
years. Models made before the 1970s were heavy-walled kettles with clamp-on
or turn-on lids. They were fitted with a dial gauge, a vent port in the form
of a petcock or counterweight and a safety fuse.
Modern pressure canners are lightweight, thin-walled kettles; most have turn-on
lids. They have a jar rack, gasket, dial or weighted gauge, an automatic vent/cover
lock, a vent port (steam vent) to be closed with a counterweight or weighted
gauge, and a safety valve.
To be absolutely certain you are getting a true reading of the temperature
inside your pressure canner you must:
- Operate the canner at the pressure and time specified in the map of altitudes
in Missouri found in the printed version of MU publication GH1451,
Before You Start To Can, Learn The Basics. Temperatures inside pressure canners
are lower at higher altitudes.
- Get rid of air trapped inside the pressure canner by venting. Air trapped
inside the canner lowers the temperature obtained at 5 pounds, 10 pounds and
15 pounds of pressure and results in underprocessing. No matter what the manufacturer's
directions say, to be safe, you should vent all types of pressure canners 10
minutes before pressurizing.
To vent a canner, leave the vent port uncovered on newer models or manually
open petcocks on some older models. Then, heat the filled canner with its lid
locked into place until the water boils and generates steam that escapes through
the petcock or vent port. When steam first escapes, set a timer for 10 minutes.
After venting 10 minutes, close the petcock, or place the counterweight or weighted
gauge over the vent port to pressurize the canner.
Weighted-gauge models exhaust tiny amounts of air and steam each time their
gauge rocks or jiggles during processing. They control pressure precisely and
do not need watching during processing. The sound of the weight rocking or jiggling
indicates that the canner is maintaining the recommended pressure. Weighted
gauges do not have to be checked for accuracy. The single disadvantage of weighted-gauge
canners is that they cannot correct precisely for higher altitudes. At altitudes
above 1,000 feet, they must be operated at canner pressures of 10 PSI instead
of 5 PSI, or 15 PSI instead of 10 PSI.
Check dial gauges for accuracy before use each year, and replace them if
they read high by more than one pound at 5 pounds, 10 pounds or 15 pounds of
pressure. Low readings cause over-processing and also indicate that the gauge
should be replaced. Gauges may be checked at most local MU Extension centers.
Handle canner lid gaskets carefully, and clean them according to the manufacturer's
directions. Nicked or dried gaskets will allow steam leaks during pressurization
of canners. Keep gaskets clean between uses. Gaskets on older-model canners
may require a light coat of vegetable oil once each year. Gaskets on newer-model
canners are prelubricated and do not need oiling. To find out if your canner
gasket has been prelubricated, check your instruction manual.
Lid safety valves are thin metal inserts or rubber plugs that relieve excess
pressure in the canner. Do not pick at or scratch valves while cleaning lids.
Use only canners that have the Underwriter's Laboratory (UL) approval for safety.
Replacement gauges and other parts for canners are often available at stores
that sell canning equipment or from canner manufacturers. When ordering parts,
be sure to give your canner model number and describe the parts needed.
Pressure canning step-by-step
- Put 2 inches to 3 inches of hot water in the canner. Place filled jars on
the rack using a jar lifter. Fasten canner lid securely.
- Leave weight off vent port or open petcock. Heat at the highest setting
until steam flows freely from the petcock or vent port.
- Maintain high heat setting, let steam vent 10 minutes and then place weight
on vent port or close petcock. The canner will pressurize during the next three
to five minutes.
- Start timing the process when the pressure reading on the dial indicates
that the recommended pressure has been reached, or when the weighted gauge
begins to jiggle or rock.
- Regulate heat under the canner to maintain a steady pressure at or slightly
above the correct gauge pressure. Quick and large pressure changes during processing
may cause jars to lose liquid. Weighted gauges on Mirro canners should jiggle
about two or three times per minute. On Presto canners, they should rock slowly
throughout the process.
- When the timing process is completed, remove the canner from heat and let
the canner depressurize. Do not force-cool the canner. Forced cooling may result
in food spoilage. Cooling the canner with cold running water or opening the
vent port before the canner is fully depressurized will cause liquid to escape
from jars and seal failures. Force-cooling may also warp the canner lid on
older-model canners causing steam leaks. Time the depressurization of older
models. Standard-size, heavy-walled canners require about 30 minutes when loaded
with pints and 45 minutes with quarts. Newer, thin-walled canners cool more
rapidly. They are equipped with vent locks that drop to a normal position allowing
the canner to be opened when the canner is depressurized.
- After the canner is depressurized, remove the weight from the vent port
or open the petcock. Wait 10 minutes, unfasten the lid and remove it carefully
tilting it away from you so the steam does not burn your face.
- Use a jar lifter to remove the jars and place them on a towel. Leave at
least one inch of space between the jars during cooling.
Allow time for a slow cool-down
When removing hot jars from a canner, do not retighten their lids. Retightening
of hot lids may cut through the gasket and cause seal failures. Cool the jars
at room temperature for 12 hours to 24 hours on towels or racks. The food level
and liquid volume of raw-packed jars will be noticeably lower after cooling.
Air is exhausted during processing and food shrinks. If a jar loses excessive
liquid during processing, do not open it to add more liquid.
Testing jar seals
After cooling jars for 12 hours to 24 hours, remove the screw bands and test
seals using one of these methods:
- Press the middle of the lid. If it springs up when released, the lid is
not sealed.
- Tap the lid with the bottom of a teaspoon. If the jar is sealed correctly,
it will make a ringing, high-pitched sound. A dull sound means the lid is not
sealed. Food touching the underside of the lid, however, will also cause a
dull sound. Test seal by another method to make sure it is sealed.
- Hold the jar at eye level, and look across the lid. The lid should be concave
(curved down slightly in the center). If the center of the lid is either flat
or bulging, it may not be sealed.
Reprocessing
unsealed jars
If a lid fails to
seal, you must reprocess within 24 hours. Remove the lid, and check the jar-sealing
surface for tiny nicks. If necessary, change the jar. Always use a new, properly
prepared lid, and reprocess using the same processing time. The quality of
reprocessed food is poor. Instead of reprocessing, unsealed jars of food can
also be frozen if headspace is adjusted to 1-1/2 inches and food is in a freezer-safe
container. Single, unsealed jars can be refrigerated and used within several
days.
Storing canned foods
Tightly sealed,
cooled jars are ready to be stored. Remove screw bands, wash the lid and jar
to remove food residue, rinse and dry jars. Label and date jars, and store
them in a clean, cool, dark, dry place -- 50 degrees Fahrenheit to 70 degrees Fahrenheit is ideal. Do not store jars above 95 degrees Fahrenheit, or near hot pipes, a range,
a furnace, in an uninsulated attic or in direct sunlight. Under conditions
such as these, food will lose quality in a few weeks or months and may spoil.
Dampness may corrode metal lids, break seals and allow recontamination and spoilage.
Freezing of canned foods will not cause spoilage unless jars become unsealed and recontaminated.
Freezing and thawing will soften food, however. If you must store jars where
they may freeze, wrap them in newspapers, place them in heavy cartons and cover
with more newspapers and blankets.
Adapted from Complete Guide to Home Canning, United States Department of Agriculture,
Agriculture Information Bulletin, number 539.
GH1452, reviewed June 2003