“QUESTIONS 
Q. How are safe process times for canned foods determined? 
~ 
A. Safe canning processes are based on laboratory studies. The process 
times for vegetables given in this publication are the result of extensive 
research by the Bureau of Human Nutrition and Home Economics. 
More than 3,700 glass jars and tin cans of vegetables were packed 
and processed in household-type containers. Penetration of heat into 
containers of food during processing was studied. From the data ob- 
tained and data on the heat resistance of known spoilage organisms, 
process times were calculated. These times were checked by experi- 
mental packs inoculated with spores of bacteria somewhat more re- 
sistant to heat than spores of the bacteria that cause botulism. 
Process times previously recommended for vegetables by the United 
States Department of Agriculture were based on commercial research, 
as are those given here for fruit. The new, more precisely determined 
directions for vegetables are based on home canning procedures and 
equipment. They call for shorter heating in the canner in many in- 
stances, and result in more attractive and palatable products. Additional 
studies in home canning may permit further improvements in procedures 
and processes. 
Q. Is it safe to process foods in the oven? 
A. No, oven canning is dangerous. Jars may seal during processing and 
explode, wrecking the stove and seriously cutting or burning persons. 
The temperature of the food in the jars during oven processing does 
not get high enough to insure destruction of spoilage bacteria in vege- 
tables without exceedingly long processes. 
Q. Why is the open-kettle method not recommended for canning fruits and 
vegetables? 
A. In open-kettle canning, food is cooked in an ordinary kettle, then 
packed into hot jars and sealed without processing. When the food is 
transferred from kettle to jar, bacteria may get in and cause food to 
‘spoil. And for vegetables, the temperatures obtained in open-kettle can- 
ning are not high enough to destroy all the spoilage organisms that 
may be in the food unless it is cooked for an excessively long time. 
Q. May a pressure canner be used for processing fruits? 
A. Yes. If it is deep enough it may be used as a water-bath canner (p. 2). 
22 
. Cooking liquid is recommended for packing most vegetables because it 
. Why is liquid sometimes lost from glass jars during processing? 
Q. Should liquid lost during processing be replaced? 
A. No, never open a jar and refill with liquid—this would Jet in ba 
AND 
Or you may use a pressure canner to process fruits at 0 to 1 pounc 
pressure without having the containers of food completely cover " 
with water. Put water in the canner to the shoulders of the jars; fasten + 
cover. When live steam pours steadily from the open vent, start count- _ ee 
ing time. Leave vent open and process for the same times given for the Be 
boiling-water bath. 
ANSWERS 
Processing of fruits at 5 or 10 pounds steam pressure is being 
studied, but information is not sufficiently complete to use for process- 
time recommendations. 
. Must glass jars and lids be sterilized by boiling before canning? 
. No, not when boiling-water bath or pressure-canner method is used. 
The containers as well as the food are sterilized during processing. But 
be sure jars and lids are thoroughly clean, and to prevent breakage 
have jars hot when filling them. : peer 
. Why is the cooking liquid used for packing some vegetables and boil- 
ing water for others? 
may contain minerals and vitamins dissolved out of the food. Boiling 
water is recommended when cooking liquid is dark, gritty, or strong- 
flavored, and it may be used if you haven't enough cooking liquid. 
Processing time is the same whether hot cooking liquid or boiling water = 
is used for packing. = 
. Loss of liquid may be due to cooking food too short a time to drive 
out the air that’s in it before packing it in the jars... packing jars too 
full . . . leaving air bubbles in the jars .. . not keeping pressure steady © 
in a pressure canner . . . lowering pressure too suddenly at the end of | 
the processing period. 
and you'd need to process again. Loss of liquid does not cause 
to spoil, Hage the food above the liquid may darken. 
