Home canning became popular during World War II. It offered families a way to supplement their food supplies in times of shortages when rationing was in effect. This was further driven by cold winters in Canada and the inability to grow produce in harsh conditions.(1) Nowadays, preserving can be used as a way to reduce household food waste. A lot of produce is wasted in households, because it is bought in bulk and goes bad before it is eaten. Preserving can be used as a means to prolong the life of these foods. In addition to reducing food waste, home canning can save you the cost of store-bought canned goods and out-of-season produce that tends to be expensive.(2)
Fresh fruits and vegetables tend to have a short shelf life, meaning that they lose their quality quickly. This is due to their high water content, which can lead to the growth of undesirable micro-organisms, activity of food enzymes, reactions with oxygen, and moisture loss. Undesirable micro-organisms live on the surfaces of fresh food and multiply quickly, causing spoilage.(2)
Preserving includes different methods of fermenting and canning. Fermenting is an easier method of preservation, because it is tolerant of imperfections in time, temperatures, and ingredient ratios. Fermented products are preserved by the actions of desirable micro-organisms, such as bacteria. In the fermentation of vegetables, the natural bacteria breaks down the sugars and can produce lactic acid. This lowers the pH, or makes the food more acidic, giving fermented foods their tangy flavour.(3)
The other method of preserving, known as canning, is more complex. There are two common ways to can: water bath canning and pressure canning. The method that is used will depend on the acidity of the food. High acid foods should be preserved using water bath canning. These foods include most fruits and vegetables. Low acid foods should be preserved using pressure canning. This includes foods such as red meats, seafood, poultry, milk, and some vegetables.(2)
Canning preserves food from spoilage by storing it in containers that are airtight and sterilized by heat. The tight seal keeps the liquid in and the air and undesirable micro-organisms that may cause spoilage out. The canning process consists of several stages: cleaning and preparing the ingredients; cooking the ingredients, depending on what the recipe calls for; filling and closing the jars; and processing (boiling) the canned products.(4) These stages are carefully followed by using safe canning practices.
Home canning has many benefits. When food is enjoyed within its natural season, it will have the best flavours and be at its peak nutrition. Canning extends the time that you can have certain fruits and vegetables at their prime flavour. Making jam uses the process of water bath canning. Canning fruits, such as blackberries, in the summer will allow you to preserve and enjoy them at times when they are not in season. This honey and thyme blackberry jam recipe will allow you to enjoy the fresh flavours of summer fruit all year long.
Honey and Thyme Blackberry Jam
Makes: 4 (250 ml) jars
This recipe uses the process of water bath canning to preserve blackberries. Blackberries are a seasonal fruit, meaning they are either expensive or not attainable in winter months, especially in geographical locations at high altitudes. Using the process of water bath canning to preserve blackberries when they are in peak season will give the delicious taste of blackberries all year round.
4 (6-ounce) containers of fresh blackberries
2 tablespoons granulated sugar
1 tablespoon and 1 ½ teaspoons low-sugar pectin
1 cup honey
2 tablespoons fresh thyme
Processing—to boil for a recommended time. Heating the filled jars at the right temperature and time destroys certain micro-organisms that will cause the food to spoil, inactivate enzymes, and vent excess air from the jar.(5)
Canner—a large pot deep enough to cover the top of your jars with at least 1 inch of water as it boils.
Rack—is placed in the bottom of the canner and elevates the jars off the bottom of the pot. This allows the boiling water to circulate around the jars.(6)
Seal—a seal and ring lid that suction the canning jar when the air is removed from the container. This will help to preserve the food.(7)
1. Sterilize empty jars: put jars right side up on the rack in a boiling water canner (or a large pot with a rack on the bottom). Fill the canner and jars with hot (not boiling) water to 1 inch above the tops of the jars. Boil for 12 minutes if at an altitude of 3,001–6,000 ft. At altitudes less than 1,000 ft., boil for 10 minutes. Remove and drain the hot, sterilized jars one at a time.
2. In a large pot over medium heat, add the berries. Crush the berries and bring to a simmer. Add in sugar and pectin. Bring to a rolling boil, stirring constantly.
3. Stir in honey, then boil hard for 1 minute. Stir in thyme.
4. Using a ladle, fill the jars with the blackberry mixture. Leave ¼ inch of headspace at the top of the jar (this accounts for expansion). Wipe the rim with a clean cloth and then run a clean spatula or chopstick around the interior of the jar, between the blackberry mixture and the glass side, to remove any air bubbles.
5. Place the round canning lids on the jars. Screw the bands onto the jars until just finger-tight. You want them to be secure but not so tight that air cannot escape during the canning process.
6. Using a jar lifter or tongs, place the filled jars on the rack inside the canner (or large pot). Make sure the jar lifter is securely positioned below the screw band of the lid. Keep the jar upright at all times, as tilting could cause food to spill into the seal of the lid.
7. Cover jars with at least 1 inch of water. Heat the water in the canner until it boils vigorously.
8. Process (boil) for 20 minutes if at an altitude of 3,001–6,000 ft., 15 minutes if at an altitude of 1,001–3,000 ft., and 10 minutes if at an altitude of 0–1,000 ft. Keep the canner covered. The water needs to maintain a boil the entire time.
9. Turn off the heat and remove the canner lid. Wait 5 minutes before removing the jars.
10. Using a jar lifter or tongs, remove the jars and place them on a towel or rack. Let jars sit, undisturbed, to cool at room temperature for 12–24 hours. Do not place directly on a counter, as the cool temperature could cause the jars to shatter.
11. Once cooled completely, test the seal by pressing the middle of the lid with a finger or thumb. If the lid springs up when you release your finger, the lid is unsealed. To test the seal again, remove the rings and gently lift each jar by the edge of its lid. If any lids fail, refrigerate the contents and consume promptly. Alternatively, if no more than 24 hours have gone by, the contents can be reprocessed using the same method, with a clean lid, and if necessary, a new jar.
12. If the seals hold, label and date your jars. Store in a cool, dry place.
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3 University of Missouri Extension—Safely Fermenting Food at Home, 2015
4 Britannica—Canning Food Processing
5 Healthy Canning—What Does Processing Time Mean in Home Canning?
6 Kitchn—How to Make Your Own Canning Equipment, 2010
7 SF Gates—How to Seal Glass Canning Jars, 2017