It’s prime gardening season here in New Hampshire and if the heat, sun and rain are producing a bumper crop of fruits and vegetables you may want to save the extras. My colleagues and I have scheduled food preservation workshops across the state so check out the schedule on our Food Safety page of our Extension website extension.unh.edu to see the upcoming sessions. In case you can’t make it, here are some of the issues you may want to be aware of before you head to the kitchen to “preserve the harvest.”
Major Canning Mistakes – Potentially Deadly
*Making up your own canning recipe. Without scientific testing, you will not know how long the product needs to be processed to be safe. Extension recommends using a USDA tested recipe to get the best tasting and safest results. Check out the USDA Complete Guide to Home Canning which can be viewed or downloaded free.
*Adding EXTRA starch, flour or other thickener to your recipe. This will slow the rate of heat
penetration into the product and can result in undercooking.
*Adding EXTRA onions, chilies, bell peppers, or other vegetables to salsas or tomato sauces. The extra vegetables dilute the acidity and can result in botulism poisoning.
*Using an oven instead of water bath for processing. The product will be under-processed since
air is not as good a conductor of heat as water or steam. The jars also may break or explode. We recommend that all home canned products be safely processed in a water bath canner for acidified vegetables and fruits. For low acid vegetables, (carrot, corn, peas, etc. or meats and seafood) a pressure canner is needed.
*Not making altitude adjustments. Since boiling temperatures are lower at higher altitudes, the
canned products will be under-processed and may not seal safely. Pressure canning requires adding more pounds of pressure while water bath canning requires more processing time.
*Not venting pressure canner. Lack of venting can result in air pockets (cold spots) which will not reach as high a temperature as is needed.
*Not having dial-type pressure canner gauges tested annually. If the gauge is inaccurate, the food may be under-processed and therefore not safe.
*Failure to acidify canned tomatoes. Not all tomatoes have an adequate acid level (pH), especially if the vine is dead when tomatoes are harvested. This can result in botulism poisoning.
*Cooling pressure canner under running water. Calculations as to processing time include the
residual heat during the normal cool-down period as part of the canning process. Hurrying this process will result in under-processed food; siphoning of liquid from the jars and jar breakage may also occur.
If you think that a canned product is not safe, don’t even taste it. To protect your family and your pets, boil the jar and contents for thirty minutes then discard both in the trash.
Minor Canning Mistakes – Economic Loss, But Results Not Deadly
*Use of mayonnaise jars. The thinner walls of the glass may break, especially if used in a pressure canner, and it may be more difficult to obtain a good seal. However, if it seals, it is safe to use.
*Use of paraffin on jams & jellies. Small air holes in the paraffin may allow mold to grow. Also, paraffin can catch on fire if overheated during preparation. If preserves do have mold growth, the recommendation is not to eat the product, but discard it.
*Storing food longer than recommended. Keeping foods longer than recommended or storing
at temperatures above 70° F for an extended period of time will decrease the quality and the value of some nutrients, but the product will be safe to eat. A darkening of fruits and change in texture is often a result as well. A general rule of thumb is to process what you can use within a year. The general guidelines for safe food preservation really are not difficult to follow. Just make certain to always use an up-to-date, scientifically-tested recipe, follow it exactly and make the altitude adjustments for time or pressure. If you have specific questions, contact the UNH Cooperative Extension Info Line at 1-877-398-4769.
Cautions Issued for Specific Foods
• Quick Breads (e.g. , banana, zucchini, pumpkin) — Baking quick breads in canning jars and then placing a lid and ring on the jar to create a vacuum seal as it cools does not kill botulism-forming organisms that grow in warm, moist, anaerobic conditions. These items should be either baked fresh and served or frozen.
• Dried Beans (pinto, kidney, etc.) — To safely can dried beans, they must be hydrated first
(usually 12 to18 hours) and then brought to a boil for 30 min. Hot beans are then placed into
hot jars for processing.
1. Always use up-to-date, scientifically tested canning recipes.
2. Only use approved, up-to-date canning methods (boiling water-bath or pressure).
3. Follow canning directions exactly.
4. Make altitude adjustments by adding more time to water bath canning or increasing pressure for pressure canned products.
5. Make certain canned products have a proper lid seal, if it was used before, throw it out and get a lid.
Note: Unless you are sure that the above general rules were followed, boil low acid foods for 10 minutes before eating them to inactivate botulism-causing organisms (clostridium botulinum).
Exceptions to the General Rules
• Changing salt level in anything except pickles. Salt acts as a preservative and adds
flavor and crispness to pickles. In other foods, it is mainly used as a flavoring agent and is added
as a personal preference.
• Changing sugar level in syrup used for canned fruit. Sugar helps fruit retain a bright
color and firm texture, but is not necessary for safety.
• Add EXTRA vinegar or lemon juice. Bottled acids help obtain required pH (acid levels) in tomatoes and pickles. If a more tart or sour flavor is desired, more vinegar, lemon or lime juice may be added.
• Decrease any vegetable except tomatoes in salsas. Salsa recipes have been tested to ensure
that they contain enough acid to be safely processed in a boiling water-bath canner. This
acid is provided by the correct amount of tomatoes. The addition of vegetables has also
been calibrated to balance the acid level. While it is dangerous to add more vegetables to salsa
recipes, fewer may be used for a milder flavor.
• Substitute bell peppers, long green peppers or jalapeño peppers for each other in salsa
recipes. So long as the total amount of peppers remains the same (or fewer) as what is listed in
the tested recipe, peppers may be interchanged.
Our food safety team wants you to get the best information to preserve food safely whether you can, freeze or dry food.
Original article by Kathleen Riggs, Utah State University Cooperative Extension, edited by Deb Maes, Extension Field Specialist in Food Safety.