Canning is a basic process in which jars of food are heated to kill bacteria and force air from the container, preventing contamination. First introduced by Nicolas Appert in the early 1800s, the process was developed as a method for preserving food for Napoleon’s mobile troops, but soon revolutionized the way food was prepared and stored around the world. Along with freezing and dehydration, canning has changed the way we grow and eat produce. For the home gardener, preserving the harvest through easy canning means summer crops can be enjoyed all year long.
Water bath processing is the easiest and most common method for canning. Using a large pot, prepared jars are submerged in boiling water for a period of 5 to 45 minutes. During this process, air is forced out of the jars to create a vacuum seal to protect the contents from the spoilage that comes from air exposure. Water bath canning works well for most canned goods, but because the processing temperature does not exceed 212 degrees F, water bath canning relies on some degree of acidity in the food to destroy the most persistent bacteria and is not an effective method for canning low-acid foods like green beans or corn without adding an acidic element like lemon juice or vinegar. Most popular methods of canning, including pickling and jelly-making, are achieved using this inexpensive method.
Low-acid foods harbor enzymes that can cause growth of bacteria, leading to botulism. Without the addition of acids, many vegetables cannot be safely canned using the water bath process because the heat produced is insufficient to kill those enzymes. Pressure canning solves this problem by processing jars under pressurized steam, which can reach the 240 degree F temperature necessary to kill bacteria without an acidic presence. Pressure canning is not difficult, but requires an investment in equipment that may not appeal to the casual canner.
A few basic tools should be in the arsenal for all canners to provide a safe and effective canning experience. Among these are a “lifter” for removing jars from a hot water bath, a magnetic wand for retrieving lids, tongs for grabbing empty jars or bands from hot water, a canning funnel for packing jars, a timer and a kitchen scale.
Inexpensive, versatile and reusable, Mason jars are the most common type of jar for canning. Ranging in size from 1/3 pint to a gallon or more, selecting the right jar for a canning task not only makes it easy to effectively can produce, it ensures portions may be parsed to maximize storage efficacy. Although Mason jars are extremely functional, they aren’t especially attractive—many companies offer “designer” jars that come in many shapes, sizes and styles.
Some types of jars rely on gaskets and clips to create an airtight seal, but the best-known and most reliable style is the Mason jar lid and band. A flat, single-use lid with a rubberized ring at the edge is placed on top of the jar and secured with a threaded band. Although the lid loses its efficacy after one use, bands may be reused many times. When canning, boiling lids and bands before use helps them create a reliable seal and ensures sterility.
One of the most important elements in canning is cleanliness. Jars that haven’t been sterilized properly beforehand can cause bacteria growth even in a sealed jar. Jars can be sterilized by boiling in water, washing in a dishwasher with a “sterilize” setting, or heating for 30 minutes in a 240 degree F oven. If sterilizing in an oven, jars should be thoroughly washed first to remove any food particles that may lurk on the surface.
Canning is an easy and economical way to prepare garden crops for long-term storage without refrigeration, but it all starts with selecting the right produce. Canning will help retain the color, flavor and texture of fruits and vegetables, but it does not improve upon the quality of fresh produce. Select only fresh fruits and vegetables that are at their peak of ripeness. Sort by size and type, exclude produce that is bruised, marred or discolored, and always wash thoroughly before canning.
Pickling is the method of food preparation most often associated with home canning. Once used almost exclusively for its powers of preservation, packing vegetables or fruit in a brine of vinegar, salt and various herbs and spices not only helps stave off bacteria, it provides a flavor profile without compare. If you can grow it, it can probably be pickled, and everything from the classic cucumber to peaches or lemons is fair game for home canners. Brines ranging from sweet to spicy help preserve produce for long-term storage though canning.
If pickles are the best-known method for processing canned produce, jams and jellies are a close second. The process relies on pectin, a naturally occurring polysaccharide that creates a firm, spreadable consistency in liquids or pureed fruits when heated and combined with sugar in carefully calculated ratios. Some types of fruit, like apples and grapes, are naturally high in pectin and can be made into jam or jelly by simply adding sugar and bringing to a hard boil, but supplemental pectin in powdered or liquid form is a common practice when trying to establish desired consistency. Jams and jellies are an easy way to can fruit surpluses for shelf-stable storage.
A 10 to 50 percent solution of water and sugar helps canned fruit retain color, texture and shape. A 10-20 percent sugar solution best approximates the flavor of fresh fruit, but increased sugar content helps to tame naturally tart fruits like sour cherries or some types of apples.
Processing jars of canned produce in a water bath or pressure canner forces the air out of jars, creating a vacuum that protects the contents from the development of bacteria. A “headspace” of at least 1/2 inch is left at the top of each jar to allow air to be pulled from the jar during sealing. Once sterile jars have been packed, wiped clean and capped with fresh lids and bands, they are lowered into a large pot filled with boiling water or locked into a pressure canner. Jars should rest on a rack to prevent contact with the bottom of the pot to prevent burning or jar breakage. Consult processing guides to determine the length of time required for the project, depending on contents, jar size and altitude to provide the heat necessary to create an airtight seal without overcooking food within. Once processed jars have been removed, they should be left to rest at room temperature. As jars cool, a *pop* should sound as the lid contracts, indicating a seal has been established. Once jars have completely cooled, press the lid down firmly. If the lid buckles when pressed, no seal is present and the jar cannot be safely stored for extended periods.
Once jars have been appropriately processed and the presence of a seal has been verified, canned food is ready to be stored. Kept in a cool dry location, many canned goods may be stored for a year or longer without significant loss of flavor or texture. Label all jars with the contents and canning date.
Originally: Canning 101: How to Can Your Own Food