Can It!

If your back yard is as full as the grocery store’s produce aisle, consider canning the bounty. Modern canning equipment makes the task safer and easier than our grandmothers had it, and it’s a great way to preserve your hard work in the garden to enjoy the rest of the year.

The most important aspect of canning is food quality. Bacteria, yeasts and molds are naturally found on the surface of fresh produce. Growth of the bacterium Clostridium botulinum can cause botulism, a deadly form of food poisoning. While spores of botulinum are on most fresh food surfaces, they only grow in the absence of air – as in canned foods. To prevent this, you must follow the specific processing times determined for various crops to destroy the largest number of heat-resistant microorganisms.

When it comes to canning, foods are classified as acid foods (with a pH of 4.6 or lower) or low-acid foods (with a pH higher than 4.6). Acid foods naturally contain enough acid to inhibit bacterial growth or destroy bacterial spores more rapidly when heated. These foods include fruits (with the possible exception of figs) – including most tomatoes. Some vegetables are acidified by adding vinegar, lemon juice or citric acid to make them “acid foods” (think pickles). Acid foods can be safely processed in a boiling-water canner in as few as 5 minutes or as many as 85 minutes – it depends on the food-specific guidelines.

On the other end of the spectrum are low-acid foods, which include all fresh vegetables (except most tomatoes), red meats, seafood, poultry and milk. Low-acid foods don’t contain enough acid to prevent bacterial growth, so the spores need to be destroyed during processing. Botulinum spores are difficult to destroy at boiling-water temperatures, so low-acid foods must be processed in a pressure canner to raise the temperature higher – to 240-250 degrees F. To destroy the botulinum bacteria, the pressure must be maintained for 20-100 minutes. (Again, it depends on the kind of food being canned, the way the food was packed into the jars and the size of the jars.)

Of course, good canning starts with the right plants in your garden. Some varieties are better suited for this kind of preservation than others, so plan accordingly. Take advantage of peak quality by processing vegetables within 6-12 hours of harvest, but allow tree fruits one day between harvest and canning for best quality. Throw out any diseased or moldy produce, trim away small spots or insect damage on the remainder, and always wash your produce before packing.

Next comes the raw packing or hot packing. Raw packing is more suitable for vegetables processed in a pressure canner. The jars are tightly filled with freshly prepared, unheated food. Once the jars are packed, boiling water is poured over the produce, filling the jar but leaving the appropriate amount of headspace – the unfilled space in the jar above the food and below the lid. This space is necessary for food expansion as the jars are processed and for vacuum formation in cooled jars. Canning specifications call for a ¼-inch headspace for jams and jellies, ½-headspace for fruits and tomatoes processed in a boiling-water canner, and 1-inch headspace for low-acid foods processed in a pressure canner.

Hot packing requires that freshly prepared food be heated to boiling, simmered for 2-5 minutes and then loosely filled into jars to the appropriate headspace. Hot packing is the preferred method for boiling-water canners. This process helps remove air from the food tissues and shrinks the produce. (Removing the air increases the vacuum in the sealed jars, improving its shelf life, and preshrinking allows more food to be packed in each jar.) The only drawback to hot packing is that it takes more time to prepare.

The big question, of course, is how long to process the food? Don’t rely on your memory from year to year for the correct times. Research-based guidelines are available from your local Cooperative Extension Service or in online publications from the USDA. Tables for proper processing include the most common variables (such as raw pack/hot pack, jar size, altitude and type of canner).

Once you’ve processed your fruits and veggies, allow the jars to cool for 12-24 hours, then test the seals. Just press down on the center of the lid – if it “pops” in and back up, the jar isn’t sealed. You should either eat the food right away or reprocess it with a new lid – and be sure to check the jars for damage. Nicks in the rim of the jar or a cross-threaded band are two probable causes for a failed seal.

Finally, wipe off the sealed jars to remove any food residue, then label each container with the date. If you’re canning several batches with some variation (i.e., some with salt or no salt), you might want to mark that on the label as well. Store the jars in a cool, dark, dry place. (Temperatures above 95 degrees F can lead to food spoilage.)

Sure, canning fruits and vegetables from your garden requires some effort and storage space (since you’ll be stockpiling several months worth of food), but you’ll be doubling the pleasure from a season’s worth of work. Just think about sitting down to a steaming plate of spaghetti with homemade sauce bursting with flavor from your tomatoes. That’s sure to bring a taste of summer straight to your dinner table!