What Kinds of Jars Can Be Used
Use only standard home canning jars. Glass canning
jars, also known as mason jars after their nineteenth
century American inventor, John L. Mason, are the standard
jars to use in home canning. These reusable jars
are produced in a variety of sizes, some with decorative
finishes for gifting. They are made to seal properly,
to be durable with repeated use and to be used safely
in a steam pressure canner. The manufacturer's name
is usually blown in the side of the jar.
jars from the grocery store, also known as packers'
jars, are not made for home canning. The jars that contain
pickles, mayonnaise or peanut butter are not made for
the rigors of home canning. Even though standard home
canning lids may seem to fit these jars, the lids may
not seal because the glass is not as thick and slightly
irregular. The jar neck may be too shallow for a standard
home canning band to hold the lid tightly against the
In addition to sealing problems with
commercial jars they may also be dangerous. Most of
them are made of thin glass and are not heat tempered,
as regular home canning jars. They may not withstand
the high pressure of canning and break. When you open
the canner, the jars may still be under pressure. The
quick drop in temperature could cause the recycled jar
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.
How to Determine If A Jar Of Canned Food
A. Cool jars for 12 to 24 hours,
remove the screwbands, and test seals
with one of the following options:
- Press the middle of the lid
with a finger or thumb. If the lid
springs up when you release your
finger, the lid is unsealed.
- Tap the lid with the bottom
of a teaspoon. If it makes a dull
sound, the lid is not sealed. If
food is in contact with the underside
of the lid, it will also cause a
dull sound. If the jar is sealed
correctly, it will make a ringing,
- Hold the jar at eye level and
look across the lid. The lid should
be concave (curved down slightly
in the center). If center of the
lid is flat or bulging, it may not
Jars To Break?
There are several types of breaks
that occur. Each break looks different
and has specific causes. Thermal shock is characterized by
a crack running around the base of the
lower part of the jar, sometimes extending
up the side. To prevent thermal breakage:
Internal pressure break is characterized by the origin of the break on the side.
It is in the form of a vertical crack
that divides and forks into two fissures.
To prevent pressure breaks:
- Avoid sudden temperature changes,
such as putting hot food in a cold
jar, putting a cold jar in hot water,
or placing a hot jar on a cool or
wet surface. Keep jars in hot water
- Use a rack in the canner.
- Avoid using metal knives or
spatulas to remove air bubbles or
steel wool pads to clean jars.
Impact breaks originate at the point of impact and fissures radiate from the
point of contact. To prevent impact
- Provide adequate headspace in
jars for food to expand when heated.
- Keep heat steady during processing.
- Avoid reducing canner pressure
under running water or lifting the
pressure control or petcock before
pressure drops to zero.
- Handle jars carefully. Jars
that have been dropped, hit, or
bumped are susceptible to breakage.
Test new jars that may have been
mishandled (to see if they break)
by immersing them in room-temperature
water, bring to a boil, and boil
- Avoid the use of metal tools
to remove air bubbles.
- Avoid using old jars. Jars have
a life expectancy of about 10 years.
Is It Safe to Re-Use Canning Jars?
can reuse standard canning jars, but be sure to caredully
inspect jars for any cracks or chips along the rim or
threads. Discard any imperfect jars because defects
prevent airtight seals.
Wash glass jars in
hot, soapy water and rinse well. When you can most food
by the boiling-water_bath method and all foods by the
pressure-canner method, it is not necessary to sterilize
jars before canning. The jars, as well as the food,
are sterilized during processing.
sterilize jelly containers in boiling water for 10 minutes
before using them. Then keep the containers hot -- either
in a slow oven or in hot water -- until you use them.
This will keep them from breaking when you fill them
with hot jelly.
Why Is Headspace
Important In Canning?
Headspace is the distance between
the surface of food and the underside
of the lid. This space allows for the
expansion of food solids or bubbling
up of liquid during processing. If headspace
is not adequate, some food in the container
will be forced out, leaving food particles
or syrup on the sealing surface and
preventing a seal. When too much headspace
is allowed, some air may remain in the
jar after processing, causing food at
the top of the jar to darken. Adequate
headspace allows a vacuum to form during
the processing of the food.
Reasons for Liquid Loss From Jars
As strange as it may seem, there are many reasons for liquid loss from jars
during processing. The following are possible reasons:
- The jar is packed too full, that is, you did not leave recommended
- The food is packed so tightly that liquid did not fill the spaces between
- Starchy foods may absorb some of the liquid.
- The liquid you added to cover cold, raw food was not hot enough when you put
it in the canner.
- You did not remove air bubbles when you packed the food. (You can do this by
running a rubber spatula between the food and the jar.)
- You did not cover jars of acid foods with one or two inches of water in the
boiling water bath canner.
- The pressure canner was not sufficiently exhausted.
- Pressure fluctuated, or the temperature lowered suddenly during processing,
due to uncontrolled heat source.
- The temperatures changed suddenly when processing was over. If the pressure
canner cools too quickly while the contents of the jar remain at a much higher
temperature, the liquid will boil over. The "coming down" period has to be
gradual and even.
- The petcock was opened before the pressure had returned to zero. When the
pressure gets to zero, open the petcock cautiously; if steam escapes, close and
wait a few minutes.
- The canner stood too long after pressure returned to zero. Open the canner
within several minutes after it returns to zero pressure.
- You removed the jars too quickly after removing the cover. Let the jars stay
in the canner for a few minutes after removing the cover, or until the boiling
in the jars goes down.
- The gauge's pointer does not rest at zero when not under pressure.
Liquid loss may cause the food to darken, but does not interfere with the
keeping qualities. Do not open jars at the end of the processing to replace
liquid before you will spoil the food, unless you use the contents
Is It All
Right To Let Jars Cool In The Water
In Which They Were Processed?
IIt is important to remove jars
from a boiling-water canner immediately
when the processing time is up. The
spores of certain thermophilic, or heat-loving
bacteria, can survive boiling-water
processing. Because these bacteria thrive
at high temperatures, they can multiply
and cause spoilage if canning jars are
left in the hot water to cool slowly.
When processing foods in a steam-pressure
canner, the canner is removed from the
heat source when the processing time
is up. Jars are left in the steam-pressure
canner until the pressure returns to
zero naturally. This period of time,
after removal from heat until the pressure
reaches zero, is considered part of
the processing time and is necessary
for destruction of microorganisms. Do
not rush this cooling by placing the
canner under water, or by using a fan.
Remove the jars immediately when the
pressure returns to zero, and cool at
The Best Way To Clean Jars Before Canning?
Before every use, wash empty jars
in hot water with detergent and rinse
well by hand, or wash in a dishwasher.
Detergent residue 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.