|Canning your own food in and Urban Environment
General Canning Information
How Canning Preserves Foods
The high percentage of water in most fresh foods makes them very perishable. They spoil or lose their
quality for several reasons:
growth of undesirable microorganisms-bacteria, molds, and yeasts,
activity of food enzymes,
reactions with oxygen,
Microorganisms live and multiply quickly on the surfaces of fresh food and on the inside of bruised,
insect-damaged, and diseased food. Oxygen and enzymes are present throughout fresh food tissues.
Proper canning practices include:
carefully selecting and washing fresh food,
peeling some fresh foods,
hot packing many foods,
adding acids (lemon juice or vinegar) to some foods,
using acceptable jars and self-sealing lids,
processing jars in a boiling-water or pressure canner for the correct period of time.
Collectively, these practices remove oxygen; destroy enzymes; prevent the growth of undesirable
bacteria, yeasts, and molds; and help form a high vacuum in jars. Good vacuums form tight seals which
keep liquid in and air and microorganisms out.
Recommended Jars and Lids
Food may be canned in glass jars or metal containers. Metal containers can be used only once. They
require special sealing equipment and are much more costly than jars.
Regular and wide-mouth Mason-type, threaded, home-canning jars with self-sealing lids are the best
choice. They are available in ½ pint, pint, 1½ pint, quart, and ½ gallon sizes. The standard jar mouth
opening is about 2-3/8 inches. Wide-mouth jars have openings of about 3 inches, making them more
easily filled and emptied. Half-gallon jars may be used for canning very acid juices. Regular-mouth
decorator jelly jars are available in 8 and 12 ounce sizes. With careful use and handling, Mason jars may
be reused many times, requiring only new lids each time. When jars and lids are used properly, jar seals
and vacuums are excellent and jar breakage is rare.
Most commercial pint- and quart-size mayonnaise or salad dressing jars may be used with new two-
piece lids for canning acid foods. However, you should expect more seal failures and jar breakage.
These jars have a narrower sealing surface and are tempered less than Mason jars, and may be
weakened by repeated contact with metal spoons or knives used in dispensing mayonnaise or salad
dressing. Seemingly insignificant scratches in glass may cause cracking and breakage while
processing jars in a canner. Mayonnaise-type jars are not recommended for use with foods to be
processed in a pressure canner because of excessive jar breakage. Other commercial jars with mouths
that cannot be sealed with two-piece canning lids are not recommended for use in canning any food at
Before every use, wash empty jars in hot water with detergent and rinse well by hand, or wash in a
dishwasher. Unrinsed detergents may cause unnatural flavors and colors. These washing methods do
not sterilize jars. Scale or hard-water films on jars are easily removed by soaking jars several hours in a
solution containing 1 cup of vinegar (5 percent acidity) per gallon of water.
Sterilization of Empty Jars
All jams, jellies, and pickled products processed less than 10 minutes should be filled into sterile empty
jars. To sterilize empty jars, put them right side up on the rack in a boiling-water canner. Fill the canner
and jars with hot (not boiling) water to 1 inch above the tops of the jars. Boil 10 minutes at altitudes of
less than 1,000 ft. At higher elevations, boil 1 additional minute for each additional 1,000 ft elevation.
Remove and drain hot sterilized jars one at a time. Save the hot water for processing filled jars. Fill jars
with food, add lids, and tighten screw bands.
Empty jars used for vegetables, meats, and fruits to be processed in a pressure canner need not be
presterilized. It is also unnecessary to presterilize jars for fruits, tomatoes, and pickled or fermented
foods that will be processed 10 minutes or longer in a boiling-water canner.
Lid Selection, Preparation, and Use
The common self-sealing lid consists of a flat metal lid held in place by a metal screw band during
processing. The flat lid is crimped around its 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 5 years from date of manufacture. The gasket
compound in older unused lids may fail to seal on jars.
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 (not metal) spatula between the
food and the jar. Slowly turn the jar and move the spatula up and down to allow air bubbles to escape.
Adjust the headspace and then clean the jar rim (sealing surface) with a dampened paper towel. Place
the lid, gasket down, onto the cleaned jar-sealing surface. Uncleaned jar-sealing surfaces may cause
Then fit the metal screw band over the flat lid. Follow the manufacturer's guidelines enclosed with or
on the box 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 rings are too loose, liquid may escape from jars during processing, and seals may fail.
If rings are too tight, air cannot vent during processing, and food will discolor during storage. Over
tightening also may cause lids to buckle and jars to break, especially with raw-packed, pressure-
Screw bands are not needed on stored jars. They can be removed easily after jars are cooled. When
removed, washed, dried, and stored in a dry area, screw bands may be used many times. If left on
stored jars, they become difficult to remove, often rust, and may not work properly again.
Equipment for heat-processing home-canned food is of two main types—boiling-water canners and
pressure canners. Most are designed to hold seven quart jars or eight to nine pints. Small pressure
canners hold four quart jars; some large pressure canners hold 18 pint jars in two layers, but hold only
seven quart jars. Pressure saucepans with smaller volume capacities are not recommended for use in
canning. Small capacity pressure canners are treated in a similar manner as standard larger canners,
and should be vented using the typical venting procedures.
Low-acid foods must be processed in a pressure canner to be free of botulism risks. Although pressure
canners may also be used for processing acid foods, boiling water canners are recommended for this
purpose because they are faster. A pressure canner would require from 55 to 100 minutes to process a
load of jars; while the total time for processing most acid foods in boiling water varies from 25 to 60
minutes. A boiling-water canner loaded with filled jars requires about 20 to 30 minutes of heating
before its water begins to boil. A loaded pressure canner requires about 12 to 15 minutes of heating
before it begins to vent; another 10 minutes to vent the canner; another 5 minutes to pressurize the
canner; another 8 to 10 minutes to process the acid food; and, finally, another 20 to 60 minutes to cool
the canner before removing jars.
These 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 1 inch of briskly boiling water will
be over the tops of jars during processing. Some boiling-water canners do not have flat bottoms. A flat
bottom must be used on an electric range. Either a flat or ridged bottom can be used on a gas burner.
To ensure uniform processing of all jars with an electric range, the canner should be no more than 4
inches wider in diameter than the element on which it is heated.
Using boiling-water canners
Follow these steps for successful boiling-water canning:
1. Fill the canner halfway with water.
2. Preheat water to 140°F for raw-packed foods and to 180°F for hot-packed foods.
3. 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.
4. Add more boiling water, if needed, so the water level is at least 1 inch above jar tops.
5. Turn heat to its highest position until water boils vigorously.
6. Set a timer for the minutes required for processing the food.
7. Cover with the canner lid and lower the heat setting to maintain a gentle boil throughout the process
8. Add more boiling water, if needed, to keep the water level above the jars.
9. When jars have been boiled for the recommended time, turn off the heat and remove the canner lid.
10. Using a jar lifter, remove the jars and place them on a towel, leaving at least 1-inch spaces between
the jars during cooling.
Pressure canners for use in the home have been extensively redesigned in recent years. Models made
before the 1970's 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 fuse.
Pressure does not destroy microorganisms, but high temperatures applied for an adequate period of
time do kill microorganisms. The success of destroying all microorganisms capable of growing in
canned food is based on the temperature obtained in pure steam, free of air, at sea level. At sea level,
a canner operated at a gauge pressure of 10.5 lbs provides an internal temperature of 240°F.
Parts of a Pressure Canner
Two serious errors in temperatures obtained in pressure canners occur because:
1. Internal canner temperatures are lower at higher altitudes. To correct this error, canners must be
operated at the increased pressures specified in this publication (USDA's Complete Guide to Home
Canning) for appropriate altitude ranges.
2. Air trapped in a canner lowers the temperature obtained at 5, 10, or 15 pounds of pressure and
results in under processing. The highest volume of air trapped in a canner occurs in processing raw-
packed foods in dial-gauge canners. These canners do not vent air during processing. To be safe, all
types of pressure canners must be vented 10 minutes before they are pressurized.
To vent a canner, leave the vent port uncovered on newer models or manually open petcocks on some
older models. Heating the filled canner with its lid locked into place boils water 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 need neither watching during processing nor
checking for accuracy. The sound of the weight rocking or jiggling indicates that the canner is
maintaining the recommended pressure. 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 instead of 5, or 15 instead of 10, PSI.
Check dial gauges for accuracy before use each year and replace if they read high by more than 1
pound at 5, 10, or 15 pounds of pressure. Low readings cause over-processing and may indicate that
the accuracy of the gauge is unpredictable. Gauges may be checked at most county Cooperative
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 per year. Gaskets
on newer model canners are pre-lubricated and do not benefit from oiling. Check your canner's
instructions if there is doubt that the particular gasket you use has been pre-lubricated.
Lid safety fuses are thin metal inserts or rubber plugs designed to relieve excessive pressure from the
canner. Do not pick at or scratch fuses while cleaning lids. Use only canners that have the
Underwriter's Laboratory (UL) approval to ensure their safety.
Replacement gauges and other parts for canners are often available at stores offering canning
equipment or from canner manufacturers. When ordering parts, give your canner model number and
describe the parts needed.
Using pressure canners
Follow these steps for successful pressure canning:
1. Put 2 to 3 inches of hot water in the canner. Place filled jars on the rack, using a jar lifter. Fasten
canner lid securely.
2. Leave weight off vent port or open petcock. Heat at the highest setting until steam flows from the
petcock or vent port.
3. Maintain high heat setting, exhaust steam 10 minutes, and then place weight on vent port or close
petcock. The canner will pressurize during the next 3 to 5 minutes.
4. Start timing the process when the pressure reading on the dial gauge indicates that the
recommended pressure has been reached, or when the weighted gauge begins to jiggle or rock.
5. Regulate heat under the canner to maintain a steady pressure at or slightly above the correct gauge
pressure. Quick and large pressure variations during processing may cause unnecessary liquid losses
from jars. Weighted gauges on Mirro canners should jiggle about 2 or 3 times per minute. On Presto
canners, they should rock slowly throughout the process.
6. When the timed process is completed, turn off the heat, remove the canner from heat if possible, 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 loss of liquid from jars and seal failures. Force-cooling may also warp the
canner lid of older model canners, causing steam leaks. Depressurization of older models should be
timed. 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 and are equipped with vent locks.
These canners are depressurized when their vent lock piston drops to a normal position.
7. After the canner is depressurized, remove the weight from the vent port or open the petcock. Wait 2
minutes, unfasten the lid, and remove it carefully. Lift the lid away from you so that the steam does not
burn your face.
8. Remove jars with a lifter, and place on towel or cooling rack, if desired.
Selecting the Correct Processing Time
When canning in boiling water, more processing time is needed for most raw-packed foods and for
quart jars than is needed for hot-packed foods and pint jars.
To destroy microorganisms in acid foods processed in a boiling-water canner, you must:
Process jars for the correct number of minutes in boiling water.
Cool the jars at room temperature.
The food may spoil if you fail to add process time for lower boiling-water temperatures at altitudes
above 1,000 feet, process for fewer minutes than specified, or cool jars in cold water.
To destroy microorganisms in low-acid foods processed with a pressure canner, you must:
Process the jars using the correct time and pressure specified for your altitude.
Allow canner to cool at room temperature until it is completely depressurized.
The food may spoil if you fail to select the proper process times for specific altitudes, fail to exhaust
canners properly, process at lower pressure than specified, process for fewer minutes than specified,
or cool the canner with water.
(Note: The following information applies to using the tables for selecting processing times given with
food products from the USDA Complete Guide to Home Canning. Other resources may not provide the
processing times and altitude adjustments in the same type of table.)
Using tables for determining proper process times
This set of guides (i.e., the USDA Complete Guide to Home Canning) includes processing times with
altitude adjustments for each product. Process times for ½-pint and pint jars are the same, as are times
for 1-½ pint and quart jars. For some products, you have a choice of processing at 5, 10, or 15 PSI. In
these cases, choose the canner pressure you wish to use and match it with your pack style (raw or hot)
and jar size to find the correct process time. The following examples show how to select the proper
process for each type of canner. Process times are given in separate tables for sterilizing jars in
boiling-water, dial-gauge, and weighted- gauge canners.
Example A: Boiling-water Canner
Suppose you are canning peaches as a hot-pack in quarts at 2,500 ft above sea level, using a boiling-
water canner. First, select the process table for boiling-water canner. The example for peaches is
given in Table for Example A below. From that table, select the process time given for (1) the style of
pack (hot), (2) the jar size (quarts), and (3) the altitude where you live (2,500 ft). You should have
selected a process time of 30 minutes.
Table for Example A
Recommended process time for Peaches in a boiling-water canner.
Process Time at Altitudes of
Style of Pack Jar Size 0 - 1,000 ft 1,001 - 3,000 ft 3,001 - 6,000 ft Above 6,000 ft
Quarts 20 min
Example B: Dial-gauge Pressure Canner
Suppose you are canning peaches as a hot-pack in quarts at 2,500 ft above sea level, using a dial-
gauge pressure canner. First, select the process table for dial-gauge pressure canner. The example for
peaches is given in Table for Example B below. From that table, select the process pressure (PSI) given
for (1) the style of pack (hot), (2) the jar size (quarts), (3) the process time (10 minutes), (4) the altitude
where you live (2,500 ft). You should have selected a pressure of 7 lbs for the 10 minutes process time.
Table for Example B
Recommended process time for Peaches in a Dial-Gauge Pressure Canner.
Canner Pressure (PSI) at Altitudes of
Style of Pack Jar Size Process Time (Min) 0 - 2,000 ft 2,001 - 4,000 ft 4,001 - 6,000 ft 6,001 - 8,000 ft
Raw Pints or
Quarts 10 6 lb 7 8 9
Example C: Weighted-gauge Pressure Canner
Suppose you are canning peaches as a hot-pack in quarts at 2,500 ft above sea level, using a weighted-
gauge pressure canner. First, select the process time for weighted-gauge pressure canner. The
example for peaches is given in Table for Example C below. From that table, select the process
pressure (PSI) given for (1) the style of pack (hot), (2) the jar size (quarts), (3) the process time (10
minutes), and (4) the altitude where you live (2,500 ft). You should have selected a pressure of 10 lbs
for the 10 minutes process time.
Table for Example C
Recommended process time for Peaches in a Weighted-Gauge Pressure Canner.
Canner Pressure (PSI) at Altitudes of
Style of Pack Jar Size Process Time (Min) 0 - 1,000 ft Above 1,000 ft
Raw Pints or
Quarts 10 5 lb