Michigan State University Extension
Preserving Food Safely - 01600947
08/03/99

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 for the correct number of minutes
* 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 altitudes above 1,000 feet, fail to
exhaust canners properly, process at lower pressure than
specified, process for fewer minutes than specified or
cool the canner with water.

Process times for half-pint and pint jars are the same,
as are times for 1-1/2 pint and quart jars. For some
products, you have a choice of processing at 5, l0, or l5
PSIG. In these cases, choose the canner pressure (PSIG)
you wish to use and match it with your pack style (raw or
hot) and jar size to find the correct process time. An
example of how to select the proper process follows.

EXAMPLE OF USING TABLES FOR DETERMINING PROPER PROCESS
TIMES

Suppose you are canning peaches as a hot-pack in
quarts at 2,500 feet above sea level. Since specific
process times may vary with (l) the type of canner
Used,(2) the style of pack,(3) the jar size and (4) the
altitude where you live, follow these steps to find the
recommended process time from one of the three following
tables:

1. Locate the correct table for your type of canner.
Look down the column labeled "Style of Pack" on
the left side of the table and locate the correct
line for hot-pack and quart jars.
2. Look across the top to find your altitude. To
determine the correct time for you, look down the
altitude column until you intersect the row you
selected in Step 1.
3. The process pressure is 10 PSIG.
4. Look under process time. All jar sizes and styles
of pack require 10 minutes.
5. Therefore, at 2,500 feet, process peaches for 10
minutes at 10 PSIG in a weighted gauge pressure
canner.

RECOMMENDED PROCESS TIME FOR PEACHES IN A WEIGHTED-GAUGE
PRESSURE CANNER 
                                     

Style                Canner Pressure (PSI) at Altitudes of   

of        Jar       Process        0-                Above   

Pack      Size      Time         1000 ft.        1001 ft.    

Hot       Pints     10 min.         5 lb.           10 lb.   

Hot       Quarts    10              5               10       

Raw       Pints     10              5               10       

Raw       Quarts    10              5               10
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