Resources for Home Preserving Tomatoes
Elizabeth L. Andress, Ph.D.
National Center for Home Food Preservation
Tomatoes can be preserved by canning, drying, freezing, or pickling. They can
also be used in creating fruit spreads like jams, jellies and marmalades.
Raw tomatoes or raw tomato products can be kept refrigerated (below
40 degrees Fahrenheit), but will spoil over time due to bacteria,
yeasts, and molds. Preserving tomatoes in oil is currently not recommended.
Oil may protect botulism organisms trapped in a water droplet. Furthermore,
oil may have a deleterious effect on lid gaskets and the at least
one manufacturer of home canning lids recommends against it.
Only boiling water or pressure canning methods are recommended
for canning foods. Older methods, such as oven canning and open-kettle
canning, have been discredited and can be hazardous (Equipment
and Methods Not Recommended from the USDA Complete
Guide to Canning 2009). The risk of botulism poisoning determines
the choice of either boiling water or pressure canners for canning
foods. In foods that are acid (pH 4.6 or lower) the microorganism
that causes botulism cannot grow. Therefore it is safe to use a
boiling water bath canner. All other foods must be canned using
tested pressure canning processes (Ensuring
Safe Canned Foods).
Tomatoes for many years were considered high acid. However, new
varieties, over-mature fruits, and tomatoes from dead or frost-killed
vines may have a pH greater than 4.6. The USDA and University-based
researchers have determined that to ensure a safe acid level for
boiling water canning of whole, crushed, or juiced tomatoes, add
2 tablespoons of bottled lemon juice or ½ teaspoon of citric
acid per quart of tomatoes. For pints, use 1 tablespoon of bottled
lemon juice or ¼ teaspoon of citric acid. Acid can be added
directly to the jars before filling the jars with product. Add sugar
to offset acid taste, if desired. Four tablespoons of 5-percent-acidity
vinegar per quart may be used instead of lemon juice or citric acid.
However, vinegar may cause undesirable flavor changes. (Canning
Tomatoes, Introduction). Here are some tested recipes from USDA
and Cooperative Extension Service sources:
Frozen tomatoes will have a mushy texture when thawed and are suitable
only for cooking, i.e. in soups, stews, spaghetti sauces, etc. Directions
for freezing raw, juice, or stewed tomatoes are found here: http://www.uga.edu/nchfp/how/freeze/tomato.html.
Tomato products, such as sauce, puree, catsup, and chili sauce,
can be frozen. Prepare as usual, cool rapidly, pack into rigid containers
Tomatoes are an excellent food to dry. They do not need blanching
and are dried to a crisp. For more details please consult this Colorado
State University Cooperative Extension Service publication: http://www.uga.edu/nchfp/how/dry/csu_dry_vegetables.pdf
The safety concerns of pickled tomatoes are the same as those for
canning tomatoes. A pH below 4.6 must be achieved before a food
can be safely boiling water canner. When pickling, commercially
prepared vinegar is typically added to achieve the necessary acidity.
Do not alter vinegar, food, or water proportions in a recipe or
use vinegar with unknown acidity. Use only recipes with tested proportions
of ingredients. There must be a minimum, uniform level of acid throughout
the mixed product to prevent the growth of botulinum bacteria. Here
are some tested recipes from USDA and Cooperative Extension sources:
Once again the safety of a tomato preserve is dependent on it's
acid level. Here are two recipes that have been tested by University
of Georgia Cooperative Extension Service:
Think creatively when planning to preserve tomatoes, but also think
"safety". There are many tested procedures and recipes available
to preserve your tomatoes. Creating your own procedures and recipes
could result in a hazardous product, since the pH range of tomatoes
is on the borderline between acid and low-acid foods.
Permission is granted to reproduce these materials in whole or in part for educational purposes only (not for profit beyond the cost of reproduction. References to commercials products, services, and information is made with the understanding that no discrimination is intended and no endorsement by the University of Georgia, U.S. Department of Agriculture and supporting organizations is implied. This information is provided for the educational information and convenience of the reader.
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