Feature Articles
Put food safety first in home canning
Eileen Yager, Communications Officer, Extension & Ag Information, University of Missouri, yagere@umsystem.edu
Don’t believe everything you hear when it comes to home canning. Two unproven methods -- oven and dishwasher canning – are getting attention, but neither are safe, according to a University of Missouri Extension expert.
“The purpose of canning is to destroy decay and
illness-causing bacteria,” said Janet Hackert, a
nutrition specialist in Bethany, Mo.
“Canning information is frequently handed down from
generation to generation,” she said, adding that U.S.
Department of Agriculture updated home-canning
guidelines in 1989.
Canned foods should be processed using one of two
methods: boiling water, also know as water-bath
processing, for high-acid foods and pressure canning for
low-acid foods. With both methods, heat forces air out
of the jars. As they cool, a vacuum forms, sealing the
jars.
Improperly canned foods provide an ideal environment for
Clostridium botulinum bacteria spores to grow. As the
bacteria multiply, they release a toxin that can cause
serious illness, and even death.
“Foods must be heated to above boiling to destroy the
bacteria. You most certainly can’t do this in an oven or
a dishwasher or a microwave. Air is not a good conductor
of heat, so food in jars placed in an oven will not heat
evenly. The food in jars will not reach the required
temperature, so the bacteria will survive,” said Hackert.
Another danger is the possibility of the jars exploding
when the oven door is opened, causing serious burns or
cuts, and destroying the oven.
Microwave oven or dishwasher processing are equally
unsafe because the jars heat unevenly, and the food
won’t reach the required temperature.
Steam and open-kettle canning -- methods that still have
followers -- also produce a weak seal and are no longer
recommended. Even heating is essential to forming a good
seal between the jar and the lid.
More advice on safe canning:
- Wash fresh produce.
- Wash jars; check for chips along the rim.
- Use flats only once.
- Have dial gauge on pressure canner checked each season.
- Gauges can be tested at county extension offices.
- Process food according to current U.S. Department of Agriculture recommendations later than 1989.
- Avoid jars with bails and caps made of glass or one-piece zinc, porcelain-lined.
MU Extension’s Quality for Keeps publications provide additional information on home canning, including “Before You Start to Can, Learn the Basics” (GH1451), “Food Preservation: Steps to Success in Home Canning” (GH1452), “How to Can Fresh Vegetables” (GH1454), “Food Preservation — Fruitful Canning” (GH1455), “How to Can Fresh Tomato Products” (GH1456), “In a Pickle” (GH1457) and “Pack a Pickled Product” (GH1459). Publications may be ordered by phone, (800) 292-0969; on the Web: http://muextension.missouri.edu/explore/hesguide/foodnut/ or from county extension centers.
Resource:
Janet Hackert, (660) 425-6434, hackertj@missouri.edu
Last Updated 10/25/2007
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