Canning meat in cans can be confusing due to dozens of can styles and sizes. Canning in glass jars is simpler and can be accomplished by using only three sizes of a glass jar: quart, pint and 1/2 pint; For these reasons we are going to advocate only a few can sizes. The selection is based on USDA research papers which recommended No. 2, No. 2.5 and No. 3 cans as suitable for home canning. We also include smaller cans which are popular among homeowners in Pacific West states, Canada and Alaska for canning fish. Furthermore, we have chosen can sizes with as few different diameters as possible, so that they can be sealed with just one sealer. When more than one can diameter is used, we have made sure that the sealer can seal them by installing a different chuck, a very simple operation to perform. Low acid foods such as meat, poultry and fish must be processed in pressure canners.
It is important to note that the seal is formed differently in cans than in jars. In glass jars the air is forcefully expelled during the heating process by the mounting pressure inside. The lid is on top of the jar and although it is secured with a ring, the seal has not formed permanently yet. During heating the soft seal allows pressurized air to escape from the jar. Upon cooling the vacuum inside the jar sucks in the lid and the softened seal makes a tight closure upon cooling.
In cans the sealing machine forms a tight connection between the lid and the body of the can. During heating the expanding air will have no way to leave and will create a lot of pressure on ends and seams of the can. In addition, the air discolors food and slows down heat penetration. So the first step in the canning process is to exhaust as much air as possible from the can before sealing.
1. Preparation - rinse the cans, but donít rinse the lids. The sealing compound is very delicate and washing lids may compromise sealing the can. Cut the meat into 1 inch cubes or any convenient size for your can. Precook meat by roasting, stewing or frying in oil or fat.
2. Packing - pack meat loosely into cans. Leave a 1/4 inch headspace between the meat and the top of the can. Salt, pepper and spices are added on top of the packed meat. Fill each packed can to 1/4 inch from top with boiling meat juices, broth, water or tomato juice. It is generally accepted that headspace should not exceed ten percent of the total can volume. Remove air bubbles by running a plastic knife around the inside of the can, to release bubbles and any trapped air.
3. Exhausting. It is important that as much air as possible is removed from the cans. Syrups and brine should be added as hot as possible.
4. Sealing - center each hot can of meat on the can sealer and place a lid on top. Bring the top of the can sealer down until it is completely engaged. Always refer to the instructions that came with your can sealer. Inspect each can to ensure that it is completely sealed. If a seam is formed incorrectly, the meat must be removed from the can, packed into a new can, exhausted to 170° F (77° C) and resealed. Correctly sealed cans need to be kept hot. They may be placed in hot water in the canner.
5. Thermal Process
Process one pound cans for 90 minutes at:
Process half pound cans for 70 minutes at:
6. Cooling - turn off the heat, remove the canner from heat if possible, and let the canner depressurize. Do not force-cool the canner. After the canner is depressurized and the pressure drops to 0, test the canner to ensure there is no more steam left. Slightly rock the weight, no steam should be released and no resistance should be felt. Remove the weight from the vent port or open the pet-cock. Depending on the size of the canner it may take from 25 to 60 minutes for the pressure to drop to 0. Wait 10 minutes, unfasten the lid and remove it carefully. Lift the lid away from you so that the steam does not burn your face. After the pressure is reduced to zero, the cover of the pressure cooker may be removed and the cans water or air-cooled. Jars must be air-cooled, as a sudden temperature drop may cause the glass to crack.
Air-cooling facilitates the transfer of heat into the air. The cans are piled in rows, allowing sufficient space between rows for efficient air circulation. Air fans will greatly improve heat transfer. This type of cooling is well suited to products in small cans, in other words, home production.
7. Storing - Check the seams of all cans. Seams should be flat and smooth, with no pointed or rough edges. No leakage should be seen around the can edges. If some cans did not seal there are two options:
Do not freeze cans as this may compromise the seal. Label the cans with the type of meat, date, processing time and pounds of pressure. You can use a permanent marker to label cans. Store in a cool dark place.
The cooling step is performed differently by commercial producers who use different pressure canners called retorts or autoclaves. Water cooling is used because water transfers heat much faster than air. Rapid cooling of the container contents prevents softening in texture or change in color of the food. Commercial producers are well aware of the importance of cooling products rapidly in order to ensure the highest quality of canned foods. The cans are loaded onto metal baskets and are inserted into retorts which can be of the horizontal or vertical type. High temperatures in those units are generated by steam or hot water which are delivered in pipes. When the sterilization process ends, cold water is introduced into the retort. Only potable quality water may be used for cooling. Commercial producers use chlorinated water to eliminate the risk of bacteria contamination in case the seal may develop a leak. The cold water causes the hot steam to condense creating an immediate pressure and temperature drop inside. The cans should be rapidly cooled to 95-105° F (35-40° C) but not much lower. This is to ensure that some residual heat still remains to dry the can exterior. Only then dry cans can be cased, stored or shipped as the possibility of post-process contamination in dry cans is remote.
Very rapid cooling, however, may create a problem, because the pressure inside cans is still high and so is the temperature. There is a significant pressure difference between the inside of the container and the inside of the retort. This may weaken the seal or even deform the cans, especially when they are of a large size. In a tall retort, the height of cold water supplies higher pressure and will counteract the pressure inside the cans. In modern equipment the ìpressure-coolingî method is practiced; a blast of compressed air is delivered into the retort when the cooling starts. This maintains pressure in the retort and counter-balances the pressure within the can, however, the temperature drops down due to the introduction of cold water.