Principles of Canning Low-Acid Foods
Meats, poultry, fish and vegetables are classified as low-acid foods (pH>4.6) and must be processed until a condition of "commercial sterility" is achieved. Commercial sterility is defined as the condition obtained by the application of heat, alone or in combination with other treatments to render the product free of microorganisms capable of growing in the product at normal non-refrigerated conditions. The product is safe to eat because the pathogenic microorganisms are either destroyed or inactivated to the extent that they pose no health risk. The product will remain shelf stable as long as the container is perfectly sealed, which is what prevents the entry of any microorganisms from the outside. Since spoilage bacteria are easily killed during heat treatment, the product has an almost unlimited shelf life as long as it is stored at proper conditions. After a year its quality, however, will start to deteriorate but the product will remain safe to eat. There are two methods of canning employed by the industry:
- Conventional canning. Home made canning fits into this description.
- Asceptic canning. Foods and equipment are both prepared separately in sterile conditions, then combined together in a sterile room. This method cannot be employed at home conditions.
Almost all of home canning is done in glass jars, but this does not mean that jars are superior to cans. If they were, commercial manufacturers will use them instead of metal cans, won't they? The cans are used everywhere: The Armed Forces, Veterans Administration, School Lunches, Needy Families Programs, Hotels, Restaurants, Colleges, Penal Institutions, Catering Services, the list is endless. The main reason why metal cans are less popular among home canners is the total lack of information on the subject. All books, manuals and guides that were written after 1950 do not mention canning in metal containers as a viable option for a hobbyist at all. The original work that was done by the USDA and other agencies culminated in 1946 with manuals on the subject of meat canning. Both methods, glass jars and tin cans were covered and processing times were given for both. However, starting with the 1988 revision, the information on canning in tin cans was omitted from all USDA editions of the 539 Bulletin, which is largely a reprint of the AWI-110 original work from 1946.
Canning in glass jars is simpler and there is less room for error, so the USDA chose the easiest path for solving safety problems: if we don't offer information, people will not be using metal cans. It seems that the USDA has taken for granted that people are not capable to comprehend a few basic procedures. Well, many of us are willing to study the subject of canning in more detail in order to make it safe, even at home. Our hat to the University of Alaska in Fairbanks; the first institution on the Internet which decided that canning in metal cans is a suitable method for a homeowner. Many homeowners in British Columbia and in Alaska are canning game meat and fish in tin cans today. Today, we can find any kind of food packed in metal cans; soups, stews, beans, chicken, noodles, fish, meat, fat, oysters, clams, the list is endless. Almost all fish is canned in metal containers. It is a sad fact that canning meat products in metal containers does not get any recognition from the USDA, at least for canning products at home, and hopefully this book will help people to understand that canning in metal containers is not the rocket since. It is confusing for a newcomer to select the right can. The next problem is to determine what type of sealer to buy that will seal a particular can. It is easy to end up with an expensive sealer which might be a good choice for sealing large cans with fruit, but a poor choice for canning meats. However, there are great little sealers that have been performing wonderfully for decades and they are a perfect choice for a home owner. The best example is the Ives-Way can sealer which has been made in the USA for 60 years. This sealer is the best kept secret on the Internet as the company has no presence online, yet its sealer is known to everybody in the industry. It costs as little as any kitchen appliance, and can seal a great variety of cans by switching inexpensive chuck adapters and spacers. The set up and adjustments are very easy and the telephone support is excellent.
The main steps in canning are:
- Filling the product into the container.
- Hermetically sealing the container.
- Thermally processing the product and the container together.
Commercial packers use containers of all shapes, sizes and materials. Glass, steel, aluminium, plastic-cardboard-aluminium combinations, plastic containers and all types of closures. Such containers are processed by specialized equipment that is not available to a hobbyist. A home owner will can his products in glass jars or in metal cans, both types of containers are described in detail in Equipment section of the book. How the product is prepared and packed will influence the heat penetration of the container and will be taken under consideration by processing authority when evaluating the process schedule of a new recipe.
Meat intended for canning should not be permitted to freeze. If it does freeze, keep it frozen until canning time because thawed meat spoils very quickly. Wash meat, if necessary, but do not soak in water. To do so dissolves meat juices and renders meat stringy. Wiping off with a damp cloth is usually all that is needed. Cut meat into convenient pieces for packing in jars. Small bones may be left in. They seem to improve the flavor and aid in heat penetration.
Meat precooked in water is more like boiled meat in texture and flavor while meat precooked in the oven resembles roasted meat. Precooking in water may be referred to as parboiling, as the fastest way to precook a large quantity of meat and is often used with chicken. Frying makes the meat harder and gives it a less desirable flavor. Pan broiling gives good results.
Glass jars - meats should be precooked in water or in the oven before being packed.
- Metal cans - meats may be:
- precooked in water or in the oven and packed hot OR packed raw and precooked in the cans while they are being exhausted before being sealed. This method gives a better flavored product as it saves all meat juice in the can, but it requires more time and space.