Home canning

For the commercial process, see canning.

Preserved food in Mason jars

A 1914 advertisement for a combination steam canner and roaster. The described method will not protect against botulism.

Home canning or bottling, also known colloquially as putting up or processing, is the process of preserving foods, in particular, fruits, vegetables, and meats, by packing them into glass jars and then heating the jars to kill the organisms that would create spoilage.

North America

Green beans in a pressure canner ready to be processed

In North America, home canning is usually done in Mason jars, which have thicker walls than single-use commercial glass jars. Unless the food being preserved has a high acid (pH <4.6), salt or sugar content (resulting in water availability <0.85), such as pickles or jellies, the filled jars are also processed under pressure in a canner, a specialized type of pressure cooker. Ordinary pressure cookers are not recommended for canning as their smaller size and the reduced thickness of the cooker wall will not allow for the correct building up and reducing time of pressure, which is factored into the overall processing time and therefore will not destroy all the harmful microorganisms. The goal in using a pressure canner is to achieve a "botulinum cook" of 121°C for 3 minutes, throughout the entire volume of canned product. Canners often incorporate racks to hold Mason jars, and pressure canners are capable of achieving the elevated temperatures needed to prevent spoilage.

The most common configuration is a Mason jar with a flat lid and screw ring. The lid is generally made of plated or painted steel, with an elastomeric washer or gasket bonded to the underside of the rim. The lid also incorporates a slightly dimpled shape, which acts as an indicator of the vacuum (or lack thereof) inside a sealed jar. A newer reusable lid is now available that uses a flat plastic disk with a reusable rubber gasket. The ring threads onto the top of the jar over the lid to hold it in place while the jar cools after processing; the ring can be removed once a vacuum has been established in the jar. Jars are commonly in either pint or quart capacities, with two opening diameters, known as "standard" and "wide mouth".

When a jar has cooled and is properly sealed, pressing the dimple on the lid will not make any sound. An improperly sealed jar will allow the dimple to move up and down, sometimes making a popping noise. Lack of this noise does not necessarily indicate that the food in the jar is properly preserved. Typically, during the cooling process, a properly sealed lid will pop once as the pressure inside the jar is reduced enough that atmospheric pressure pushes the lid inward.

Older variations had a ceramic seal inside a one-piece zinc lid. Another method that is no longer recommended was the use of layer of hot paraffin wax poured directly over the top of the food (especially jams and jellies) to seal it from air, thus reducing growth of aerobic microorganisms like mold.

While it is possible to safely preserve many kinds of foodstuffs, home canning can expose consumers to botulism and other kinds of food poisoning if done incorrectly. The most common source of food-borne botulism is home-canned foods prepared in an unsafe manner. Safety measures must be taken when performing home canning, since ingestion of toxin in food produced by Clostridium botulinum can cause death. Because of the high risk of illness or death associated with improper canning techniques, the United States Department of Agriculture (USDA) considers it critical that consumers who intend to can at home obtain proper and current information from a reliable source. At the basis of these recommendations is the balance between bringing the food to a high enough temperature for a long enough time that spoilage and disease-producing microorganisms are killed, while not heating the food so much that it loses nutritive value or palatability.

Food safety precautions (Steps for Home Canning)

Thoroughly wash food items

Boiling process

• Preparation methods and processing times for canning. Differs for each food, for partial list, see the following link [2]

File:Pressure Canner.jpg

Pressure Canner

• Kills the spore-forming bacteria

Pressuring process

• Usually pressurize foods at 10 pounds per square inch (psi); add 1/2 psi per 1,000 ft. of elevation
• This process will kill the spores and denature the toxin

Prior to consumption:

• Boil home canned veggies first
• Boil for 10 minutes plus 1 minute per 1,000 ft of elevation
• Home canned fruits – use boiling water bath

Acidic foods are less likely to induce botulinum toxin production because low pH inhibits germination. Tomatoes are an unlikely food vehicle because of the acidity.

• Add acid (vinegar, lemon/lime juice) to lower pH but in acidic foods like tomatoes and fruits, germination may still occur if molds or other bacteria are present.
• Molds or other bacteria can raise the pH.

United Kingdom

In the United Kingdom home bottling is done with Kilner jars in a similar way to the Mason jars in the USA, and although old-style Kilner jars have a glass lid without a "dimple" more recent varieties do.

Australia

Weck glass with rubber seal and steel tension clips. The red tongue showing downwards indicates an intact sealing

In Australia the most popular home canning system is Fowler's Vacola. This system uses glass jars, single use seals, and metal lids. During the canning process the lids are secured by metal tension clips which are removed once a vacuum seal has formed. Fowler's Vacola products are still produced and are available from some hardware stores. Used equipment is frequently sold on online auction sites and in opportunity shops.

Germany

In Germany the most popular home canning system is Weck. This system uses glass jars, reuseable rubber seals, and glass lids. During the canning process the lids are secured by steel tension clips which can be removed once a vacuum seal has formed. During storage the vertical position of the rubber seal's external tongue indicates the status of the sealing. Weck products are still produced and are available from German hardware stores. Used equipment is frequently sold on online auction sites and in opportunity shops.

See also

• Canning
• Food preservation
• Pickling
• Pressure cooking

External links

• USDA Complete Guide to Home Canning
• How Do I? ...Can, from the National Center for Home Food Preservation
• Preservation: Canning, Freezing & Drying from the South Carolina Cooperative Extension at Clemson University
• Richard Roller Papers, documents the history of glass manufacturing, with an emphasis on fruit and vegetable canning jars at the Ball State University Archives and Special Collections Research Center
• "Pressing Lids Seals Fruit Jar; Gasket Molds to Rim" Popular Mechanics, December 1943 article right-middle of page