MEATS AND VEGETABLES

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.

Cooling.

Filling Containers

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. 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 Preparation

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.

Precooking Meat

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.

Low-Acid Acidified Foods

A considerable safety margin can be introduced into processing time by acidifying the product. If the low acid food, for example cucumber, is acidified to a pH of 4.6 or less, it crosses the threshold that separates low acid foods from the high acid foods. In other words it becomes a high acid food and as such, it requires less severe thermal treatment to achieve sterility. It can, theoretically, be sterilized in a water bath canner (212° F, 100° C). As the thermal resistance of bacterial spores decreases in an acidic environment, they should not grow in foods with a pH below 4.6. Thermal treatment is needed to kill only spoilage bacteria, molds, yeasts and enzymes, all of which can be killed at 212° F, 100° C.

Adding citric acid, lactic acid, lemon juice or vinegar will lower the pH of the product and cooking media. Chicken that was marinated overnight with salt, vinegar, white wine or lemon juice will acquire some acidity and will be more hostile to any bacterial spores than a fresh chicken. A pH meter is needed to measure acidity levels accurately, the pH color strips are suitable for checking water pH in a fish tank or for general less critical applications. Meats, poultry, fish, vegetables and dairy products fall into a pH range of 5.0-6.8. These are low-acid foods so they must be processed at 240-250° F, 116-121° C, unless they become acidified to such an extent that the pH equilibrium of the finished product is pH 4.6 or lower. Acidified foods do not automatically fall into the high-acid food category, they become low-acid acidified products. As mentioned earlier, acidifying foods and establishing new processing times must be left to properly trained persons and a homeowner should follow the rules established by USDA guidelines without regard to the extra acidity that he may have introduced.

Preparing Meat and Poultry

Keep all meat at low temperature until ready for processing. If meat must be kept for longer than a few days, freeze it. Trim meat off gristle and fat. Fat left on meat will melt and climb the sides of the jar during canning. If it comes in contact with the sealing edge of the lid, the jar may not seal. How you cut your meat will depend upon the end product use. If possible, always use fresh meat as it has the lowest bacteria count. Fresh home-slaughtered red meats and poultry should be chilled and canned without delay. Keeping meat in a refrigerator significantly slows down the growth of bacteria, but they still manage to multiply. The more bacteria in the meat, the longer time is needed to eliminate them, even at higher temperatures. Frozen meat may be canned, but it does not make a high quality product. For best results it is better to cut frozen meat into strips 1 to 2 inches thick and plunge into boiling water. Simmer until the color of the meat has almost disappeared, then immediately pack and process. When you must use the frozen meat thaw it in the refrigerator or place the wrapped meat under cold, running water. Trim away all freezer burn. Freezer burn does not affect the quality of the final product, as long as it is removed prior to processing. Smaller diameter cuts may be thawed in a microwave. Thawing results in a loss of natural meat juices and results in about 1-3% weight loss as some of the internal water leaks out. Frozen meat may have a small amount of "freezer burn" on the surface which should be discarded. Freezer burn occurs when frozen food has been damaged by dehydration and oxidation, due to air reaching the food. It is generally induced by substandard (non-airtight) packaging.

Meat Colour

The color of fresh meat is determined largely by the amount of myoglobin a particular animal carries. The more myoglobin the darker the meat, it is that simple. Going from top to bottom, meats that contain more myoglobin are: horse, beef, lamb, veal, pork, dark poultry and light poultry. The amount of myoglobin present in meat increases with the age of the animal. Different parts of the same animal, take the turkey for example, will display a different colour of meat. Muscles that are exercised frequently such as legs need more oxygen. As a result they develop a darker colour unlike the breast which is white due to little exercise. This colour is pretty much fixed and there is not much we can do about it unless we mix different meats together. The colour of cooked (uncured) meat varies from greyish brown for beef and grey-white for pork and is due to denaturation (cooking) of myoglobin. The red colour usually disappears in poultry at 152° F (67° C), in pork at 158° F (70° C) and in beef at 167° F (75° C). The colour of cured meat is pink and is due to the reaction between nitrite and myoglobin. The colour can vary from light pink to light red and depends on the amount of myoglobin a particular meat cut contains and the amount of nitrite added to the cure.

Nitrates

Adding nitrates to meat offers many benefits:

Meat becomes pink

Acquires a slightly different flavor

Slows down oxidation

Inhibits Cl. botulinum from growing

Sodium nitrite, commonly used as cure #1, is the strongest agent for preventing growth of Cl.botulinum spores during smoking meat. It is also added to impart the pink colour to processed meats like ham and sausages. You wouldn't like to eat gray ham, would you? Well, without sodium nitrite a roasted leg of pork is just a roasted leg, once the sodium nitrite is added it becomes pink ham with its distinctive flavor that sodium nitrite also provides. Adding sodium nitrite (cure #1) to canned meat will definitely lower the resistance of bacterial spores to thermal processing, but as explained earlier a hobbyist should still process foods according to the USDA guidelines.

Nitrate Safety Concerns

There has been much concern over the consumption of Nitrates by the general public. In the 1970's much research was done on the effects of nitrates on our health. Millions of dollars were spent, many researchers had spent long sleepless nights seeking fame and glory, but no evidence was found that when Nitrates are used within the established limits they can pose any danger to our health. A review of all scientific literature on nitrite by the National Research Council of the National Academy of Sciences indicates that nitrite does not directly harm us in any way. All this talk about the danger of nitrite in our meats pales in comparison with the amounts of Nitrates that are found in vegetables that we consume every day. The Nitrates get to them from the fertilizers which are used in agriculture. Don't blame sausages for the Nitrates you consume, blame the farmer. It is more dangerous to one's health to eat vegetables on a regular basis than a sausage. You don't need to use nitrites, however, there are many cases when you want meat to stand out, you want it to be the show meat. The example is red colour of tongue in blood sausage or red meat in a headcheese. If you want your canned meat be of red colour, use sodium nitrite (cure #1), its that simple. Curing is an important part of sausage making technology, so we will touch it very briefly as this book is about canning meats. If you want to study curing in more detail, read "Home Production of Quality Meats and Sausages."

What is Curing?

In its simplest form the word "curing" means "saving" or "preserving" and the definition covers preservation processes such as: drying, salting and smoking. When applied to home made meat products, the term "curing" usually means "preserved with salt and nitrite." When this term is applied to products made commercially it will mean that meats are prepared with salt, nitrite, ascorbates, erythorbates and dozens more chemicals that are pumped into the meat. There are dry and wet methods (brine) of curing. Meat for sausages is usually diced into 1-2 inch pieces, mixed with salt and cure #1 (2.5 g=1/2 tsp of cure #1 per 1 kg of meat) and left for 72 hours. Larger cuts of meat will benefit from injecting them with curing solution at 10% of solution per weight of the fresh meat.

Mild curing solution (21 salinometer degree):

3/4 cup of salt, 1 gallon of water, 2 tsp. of cure #1.

Inject meat or chicken with 10% of curing solution in relation to the weight of the meat, eg. 100 ml brine for 1 kg (2.2 lb) chicken. Immerse chicken in remaining brine and cure overnight in refrigerator. There may be circumstances when there is no time to cure meat properly. In such cases, the curing process, especially the development of colour will benefit greatly from cure accelerators, the simplest one being ascorbic acid which is vitamin C. When added to finely ground or emulsified products (e.g., luncheon meat), they can be canned almost immediately, and a uniform colour will be attained. A vitamin C tablet may be pulverized and applied to meat. It is usually applied at 0.1%, e.g., 1000 mg vitamin C per 1 kg of meat. Injecting meat with curing solution will increase its juiciness by decreasing cooking loss during precooking. It will also facilitate thermal processing as more meat will be subjected to convection heat transfer. Lastly, sodium nitrite is the strongest agent that inhibits the growth of Cl.botulinum spores and that is why it is always added to meats that would be smoked. Depending how the smokehouse is designed, there could be a little air inside or none at all creating favorable conditions for bacteria spores to grow.

Precooking Meat

Precooking meat prevents meat pieces from sticking together. It also provides better appearance and flavor. Precooking results in size reduction allowing meat cuts to be packed more tightly. Meats can be packed directly into containers, packed with liquid or mixed with vegetables, for example a stew. Ground beef can be mixed with spices (chili con carne) or mixing with spices and beans (chili con carne with beef). Some products such as pates or luncheon meat require additional preparation steps.

Preparing Fish

Fish should be prepared immediately after the catch. When you catch fish, handle them with care to avoid bruising. Beware that exposure to the sun or heat may cause the quality of the fish to deteriorate. Bleed fish immediately after catching to increase the storage life. Remove internal organs and rinse the fish inside and out. Keep fish iced, refrigerated, or frozen until ready to process. Keep fish between 32-40° F (0-4° C) for no longer than one to two days.

You can use either fresh fish or frozen fish for pressure canning. Many Alaskans freeze their catch for up to one year. When fishing season arrives again the fish remaining in the freezer are canned. This gives the fish an effective shelf life of two years. When using frozen fish thaw it in the refrigerator or place the wrapped fish under cold, running water.

There is little we can do to control the composition of the fish flesh as in most cases fish are harvested wild. The living fish flesh is bacteria free. Bacteria is present on the skin, gills, and in the viscera, however, they cannot penetrate the flesh while the fish is alive. The fish flesh becomes contaminated with bacteria during handling and preparation. The sooner the fish can be processed the smaller the number of microorganisms it will contain. Poor quality fish that has been invaded by microorganisms can be characterized by the presence of slime, discoloration of the gills and eyes and loss of flesh texture. To minimize microbial contamination, the fish surface must be scrupulously washed, gutted and rinsed inside. The gills must always be removed. The fish that will be canned must have the scales removed. The scales will fly everywhere so it is wiser to perform this operation outside. After cleaning, the fish has to be washed again. Previously frozen fish can be thawed, then brined and smoked.

Lobster and crab spoil very quickly after death. For this reason lobsters and some crabs are cooked alive in boiling water or weak brine (3-5%) to inactivate enzyme activity.

Shrimp can be cooked and peeled, or peeled raw and then cooked to harden the texture and cause the shrimp to curl. Oysters and clams often contain mud or sand on the exterior and should be well washed before opened. Precooking in boiling water kills the animal, opens the shell and firms the meat.

There are circumstances in which a canner will select a process which is more severe than that required for commercial sterility, as for instance occurs when bone softening is required with salmon or mackerel. Large fish are precooked whole in a steam kettle or cut into sections and precooked in brine.

Small fish are precooked in steam which removes moisture and oil that otherwise will be released in the container during thermal processing. That would adversely affect the texture, appearance and flavor of the product. This cooked out liquid should be drained away.

Precooked fish should be cooled as fast as possible to firm up the flesh to prevent breaking up the flesh during packing into the containers. The packing should follow immediately after.

Brining

Fish will benefit from immersing them in a strong brine (80 salinometer degrees), even for a short time. This toughens the surface of the flesh and removes traces of blood. The whole fish may be brined for 45 minutes, small fish or fillets for 5-15 minutes.

Smoking

Fish like other meats can be smoked by different smoking methods. Smoke temperature and the length of smoking will influence the taste of the fish. All fish may be smoked, but the fatty ones absorb smoke better, stay moister during smoking and taste better.

Ingredients

Salt, spices and condiments will improve flavor. Oil, brine, tomato juice, water or sauces improve appearance and flavor and enhance the heat penetration during thermal processing.

Packing Fish

Commercially canned fish is packed tightly to prevent it from shaking around and breaking into small pieces. It is also weighed to meet the requirements on the label. Fish that is processed at home must be cut in a way to best utilize the height of the container. Fillets can be rolled around the can, the shorter ones going inside the can. That is why the 307 x 22.25 can is so well adapted to canning fish.

The tall salmon can, 301 x 408, is another can that is great for canning a variety of fish. Both of those 2-piece cans are tapered which makes them especially attractive for storing at home as they nest inside each other.

Fish packed in jars should be neatly arranged to take advantage of the display properties of the glass, however, due to the shape of a glass jar it is harder to neatly remove the delicate product.

Thermal Process

Low-acid foods such as meat, poultry, fish and vegetables must be processed at 240-250° F (116-121° C) temperatures to kill Clostridium botulinumspores. Low-acid foods means any foods, other than alcoholic beverages, with a finished equilibrium pH greater than 4.6 and a water activity (Aw) greater than 0.85. Tomatoes and tomato products having a finished equilibrium pH less than 4.7 are not classified as low-acid foods. In an open kettle at sea level, water boils at 212° F (100° C) which is insufficient for destroying Cl.botulinum spores. At increased pressures water boils at higher temperatures, hence the need for a pressure canner. Developing the processing time for a food product to be canned is a complex and expensive process. It depends on:

The number and the type of bacteria present in the food.

The rate of heat transfer through a food in a given container.

The temperature and the time of the heating.

The pH of the food.

In the past, the USDA working with the National Canners Association conducted thermal processing studies for different foods. To determine a processing time for each food, bacteria which were more heat resistant than Clostridium botulinum were introduced into sample jars. The test organism was putrefactive anaerobe No. 3679, isolated by Cameron in 1927 in the laboratories of the National Canners Association. The spores of the organism exhibit a resistance to heat almost twice the maximum resistance reported for Cl. botulinum under the same conditions. The jars were heated for different times, then they were held and tested for spoilage. At each temperature and processing time the reading was taken when bacteria started to die. The results of the tests were plotted on a graph where a single curve called Thermal Death Time displays the findings. The calculated times were verified by actual tests with jars inoculated with known quantities of bacteria. A margin of safety was introduced and the processing time and temperature for a particular food in a given jar was established. The United States Department of Agriculture Information Bulletin No. 539 lists detailed processing times for a great variety of foods.

The table below demonstrates the importance of time-temperature combinations for killing bacteria. The information comes from Putra University, Malaysia: From thermal death curves, the following time/temperature treatments yield the same microbe killing effect:

Time-temperature relationship.

Factors Influencing Heat Transfer

Heat is transferred from the outside of the jar/can to the interior of the solid canned food through conduction. This is a slow method as the heat is transferred by molecule-to-molecule transfer. Meats, poultry, fish, potatoes and beets are heated by conduction. The last portion heated, the so called "cold spot" is usually the geometric centre of the container.

Transfer of heat in solid food in a jar during steam processing.

Transfer of heat in liquid or semi-liquid food in a jar during steam processing.

Heat transfer in liquids is by convection. The convection method is faster as the heat is transferred by the moving currents of liquid itself. Meat broth or soup with a few solid pieces will heat much faster than a broth with solid chunks of meat. Therefore, where possible, it is important to have the food in smaller cuts and surrounded by liquid to allow these currents.

In liquid or semi-liquid foods the critical thermal point (cold point) is located about 1/3 of the height from the bottom of the container. A smoked sausage can be baked in a smokehouse to a safe internal meat temperature by raising the temperature to about 176-190° F, 80-88° C, which is a slow process. The same sausage immersed in hot water 176° F, 80° C will cook much faster as water conducts heat much faster than air. For that reason, the majority of processed meats are cooked in water. To take advantage of the shorter heating times of the convection method, liquid is added to solid chunks of food and a combination method (conduction-convection) is created. Liquid convection currents supply heat to solid food where the heat is transferred by a conduction method (molecule heat transfer). Heat penetration into meat and poultry is accomplished principally by conduction, with convection playing a lesser role. However, when products are packed in brine, broth or other liquid, convection heating plays a bigger role. There are many cans on the market and they come in different shapes and sizes. A good understanding of the subject of heat transfer will make can selecting much easier.

Regulate heat to maintain a steady, constant pressure. Fluctuating pressure causes loss of liquid from glass jars and uneven cooking of contents.

Home and commercial canning equipment and methods differ greatly. Slower heating and cooling times with home equipment account for the greatest difference. Canning recipes for homeowners are designed with safety in mind, taking under consideration that a hobbyist works without supervision from food inspectors.

The efficiency of heat transfer in containers depends on:

The size and shape of the container - small diameter container will heat faster.

Physical properties of the food product - food with a higher moisture content will heat faster. A freshly stuffed sausage will contain more moisture than a sausage that was conditioned for 2 hours at room temperature and then smoked for 3 hours.

Heat transfer characteristics of the heating medium - water, broth, syrup, sugar, gravy, all those factors affect the heat transfer. Starchy ingredients absorb liquid during processing, and change the heat transfer process. When heated, the starch thickened gravy will change its state from a liquid to a more solid state and will affect convection currents and heating times. Fats and oils greatly retard thermal death of bacterial spores, vegetative cells and yeasts. For this reason fatty meat or fish requires longer processing times. Sodium chloride is the main factor controlling meat spoilage in regular meat processing. Elevated salt levels make production of dry hams or traditionally cured salami possible. However, in the canning process salt is of little importance as heat is the main safety hurdle. When salt is applied up to 4%, the spores display increased resistance to heat. Only at levels over 8%, the resistance of spores to heat treatment decreases. Unfortunately, such high salt levels will make the product unpalatable.

Heat transfer characteristics of the container - the thickness of the glass or a metal can, type of metal (steel, aluminum). The tightness of the pack will affect the movement of the currents as they will face less or more resistance. The way the material is cut will influence the movement of the current, for example vertically packed carrots or diced carrots.

Under processing can result in spoiled food, while over processing results in overcooked food.

Canning Meat in Glass Jars

Canning meat in glass jars process:

Preparation

Packing

Sealing

Thermal process

Cooling

Storing

1. Read the manufacturer's instructions on the use of your pressure canner. Use only standard jars intended for home canning. These jars will have the manufacturerís name molded in the glass. Never use jars from commercial food products.

2. Either a raw pack or hot pack method may be used. Add salt (1/2 teaspoon per pint jar, 1 tsp for quart jar) and spices into the empty container. Leave 1 inch headspace in glass jars.

Raw pack - use raw meat, do not brown. Raw meat is packed directly into jars. Do not tightly pack the jars. Add only meat and seasonings, don't add liquid. Raw meat will release its own juices during the canning process.

Hot pack - brown meat before packing. Brown the meat in a skillet with a small amount of fat. The meat shrinks and can be packed more tightly. Save the liquid which will be added (hot) to the jars after packing. If more liquid is needed, add broth, tomato juice or water.

NOTE it is common to sterilize jars when using a water bath canner. What about a pressure canner? Jars that will be processed in a pressure canner don't have to be sterilized as the high canning temperatures will sterilize them anyhow. Run a plastic utensil around the inside of the jar to free bubbles and remove excess air.

3. Wipe off the rim of the jar and place the lid on top. Secure the lid with a screwband, finger tight.

4. Put 2 to 3 inches of water in the canner. The temperature of the water should be similar to the temperature of the product; this prevents stress on the glass jar. Place filled jars on the rack, using a jar lifter. Fasten the canner lid securely. Leave the weight off the vent pipe. Heat at the highest setting until steam flows freely from the vent pipe. This pushes the excess air out of the canner through the vent port. If the canner is not exhausted, the inside temperature may not correspond to the pressure on the gauge. While maintaining the high heat setting, let the steam escape continuously for 10 minutes and then place the weight on the vent pipe. The canner will pressurize during the next 3 to 5 minutes. Turn the heat down slightly when the canner reaches about 7 psi, then wait for the pressure to build up. Wait until a dial indicates 11 psi or the 10 pounds weighted gauge starts to jiggle. Now you can start timing the process.

• Process meat and poultry in half pints and pints for 75 minutes and quarts for 90 minutes.

• Process fish in half pint and pint jars for 100 minutes.

• Process fish in quart jars for 160 minutes.

Regulate heat under the canner to maintain a steady pressure at or slightly above the set gauge pressure. Quick and large pressure variations during processing may cause unnecessary liquid losses from jars. The pressure must be maintained in order to hold the lids in place during processing and in the early stages of cooling so that the pressure in the canner always exceeds the pressure inside the container. Follow the canner manufacturers directions for how a weighted gauge should indicate it is maintaining the desired pressure.

NOTE if at any time pressure goes below the recommended amount, bring the canner back to pressure and start the timing of the process over again, from the beginning (using the total original process time). This is important for the safety of the food.

5. When the timed process is completed, turn off the heat, remove the canner from heat if possible, and let the canner depressurize. Do not force-cool the canner. Allow the pressure to drop naturally, dont apply cold water, cold cloth or remove the weight until the pressure drops completely. Forced cooling may result in unsafe food if the cooling period has been included as a part of the thermal process. Cooling the canner with cold running water or opening the vent port before the canner is fully depressurized will cause loss of liquid from jars and seal failures. 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 pipe or open the pet-cock. 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. Depending on the size of the canner it may take from 30 to 45 minutes for the pressure to drop to zero. Remove jars with a jar lifter, and place them on a towel or a cooling rack. Do not retighten lids after processing, you may damage the seal. Let jars sit undisturbed to cool at room temperature for 12 hours. Never rush the cooling process or jars may break. Jars should be cooled in an area away from drafts. Air blowing on hot jars may also cause breakage. Jars will seal as they cool. The jar lid will pull in when a vacuum is formed. Test the seals.

6. Label the jars with the type of meat, date, processing time and pounds of pressure. Store in a cool dark place. The screwbands may be removed. Do not freeze jars as this may compromise the seal.

Canning Meat in Cans

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.

Preparation

Packing

Exhausting cans

Sealing

Thermal process

Cooling

Storing

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.

• Place the canner rack on the bottom of the canner. Exhaust only one layer of cans at a time. Place open, filled cans inside the water in the canner. Add enough water to come half way up the sides of the open cans filled with meat.

• If you have more than will fit in one layer, put the second layer in a different pan and heat it separately. Place cans in the water where the liquid comes about halfway up the sides. Set the open cans filled with meat in a single layer in simmering water in open roasting pans on the stove. Do not cover the canner or the pan, otherwise condensing moisture will drop into the cans.

• Adjust the temperature so the water comes to a gentle boil. Check the temperature of the meat in the cans with a meat thermometer. The internal temperature of the meat in the center of the can must reach 170° F (77° C)

• Remove cans from the boiling water using a jar lifter. Carefully clean the edges of each can with a towel.

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 - Add 2-3 inches of water to the canner and place the rack. The water temperature should be similar to the temperature of the product in the can. The procedure for canning metal cans is similar to the one for canning glass jars. Cans may be stacked in the canner. When your canner is filled, fasten the lid securely. Turn on the heat.

• Leave the weight off the vent port or open the pet-cock. Heat at the highest setting until steam flows freely from the open pet-cock or vent port. This pushes the excess air out of the canner through the vent port. While maintaining the high heat setting, let the steam flow (exhaust) continuously for 10 minutes and then place the weight on the vent port or close the pet-cock. The canner will pressurize during the next 3 to 5 minutes. Wait until a dial indicates 11 psi or the 10 pounds weighted gauge starts to jiggle. Now, you can start timing the process. Write down the starting and ending time.

Cans and lids: Tall, 1 pound (size: 301 x 408) or flat, 1/2 pound (size: 307 x 200.25), also called Alaska salmon cans, are used for canning meats. According to the University of Alaska in Fairbanks, plan to use 1 to 1/2 pounds of trimmed meat per 1-pound can; 3/4 pound of trimmed meat per 1/2 pound can.

Process one pound cans for 90 minutes at:

• 10 psi - weighted gauge

• 11 psi - dial gauge

Process half pound cans for 70 minutes at:

• 10 psi - weighted gauge

• 11 psi - dial gauge

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.

Cooling Cans in Home Production

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.

Remove the cans and place them on a towel or a cooling rack. Let cans sit undisturbed to cool at room temperature until dry. This is the same procedure as used for glass jars, however, they have a strong seal and can be moved around. You may follow the same procedure for glass jars and let cans cool by themselves for 12 hours. You may gain extra safety, but you still continue to cook the product for a while.

The cans are still hot as the temperature was about 212° F (100° C) (0 psi) when the canner was depressurized. At the end of the canning process the productís temperature is 240° F (116° C). Depending on the size of the canner it may take 30-60 minutes for the canner to drop to 0 psi and 212° F (100° C). The temperature in the canner is equivalent to barbecuing at a low setting and this additional time still cooks the product. After depressurizing, the hot cans may be taken out of the canner and allowed to cool by themselves or be inserted in cold water. They already have a strong seal and can be moved around. Smaller cans, No. 2, No. 2.5 and even No. 3 can be immersed in cold water and cooled to 95-105° F (35-40° C), but not lower. Then, they must be placed on a rack and allowed to dry.

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:

• Freeze the contents of the unsealed can, or refrigerate the product and use within 3 to 4 days. Alternatively, the meat may be reprocessed in a new can within 24 hours of the initial processing period.

• Reprocess the meat in a new can within 24 hours of the initial processing period. Reprocessing does not affect the safety of the meat, however, it will affect its texture, after all, the product is cooked a second time.

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 pressure-cooling 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.

Canning Fish and Seafood

Caution No container larger than a pint jar or No. 2 can should be used in the home canning of fish because difficulties in sterilization make the use of larger sized containers unsafe. Read USDA recommendations for processing fish in quart glass jars that follow. When canning halibut or other lean fish, up to 4 tablespoon of olive oil or vegetable oil may be added to each pint jar. The oil will add moisture to the product but will also increase the calories (1 Tbsp of oil = 135 cal).

Salt, seasoning salt, or other spices may be added to the packed fish.

Sauces

Sauces may be added to containers before sealing them or served with cooked canned fish. Tomato Sauce. This sauce is often added to sardines, herrings, mackerel fillets and smoked fish. Tomato "fish sauce" is a type of ketchup made from tomato pulp, vinegar, onion, salt and spices. Bay leaves and cloves are often added.

Sugar tends to caramelize at high temperatures so it should be added in small quantities as it may darken the sauce.

Tomato Sauce for Canned Fish

1 qt ripe whole tomatoes

1 Tbsp chopped parsley

4 cloves

1 bay leaf

1/2 tsp salt

1 medium onion

1 Tbsp vinegar

1 Tbsp Worcestersire sauce

1/4 tsp cayenne pepper

Smash tomatoes and simmer with other ingredients until reduced to about half of the original volume. Strain through a fine strainer.

Mustard Sauce.

This sauce is often added to sardines and other canned fish. Ingredients: mustard seed, vinegar, cayenne pepper, turmeric, salt, water.

Add 2 Tbsp vinegar to 1 cup of water. Add 5 Tbsp. cracked mustard seeds, 1/4 tsp cayenne, 1/2 tsp turmeric. Cook in skillet for 5 minutes. Strain.

Caution Do not use starch, flour or any artificial thickening agent.

Canning Fish in 1/2 Pint and Pint Jars

Half-pint, pint or quart jars are suitable for canning fish. Fresh or frozen fish can be used, thaw frozen fish in the refrigerator. Prepare fish using general cooking procedures: bleed and gut fish immediately after catching. Make sure you remove gills. Remove the head, tail, fins and scales. You can leave bones in salmon and herring as they will soften during processing and storage. Remove the bones from halibut, when in doubt remove the bones. Cut fish into fillets or chunks which are best suited for the jar or can that you are using. The skin may be left on or off. Fillets may be rolled for packing. Salmon, trout, mullet, herring are oily fish so no oil is needed, however, lean fish like halibut or cod will benefit from additional fat or oil. Follow the same procedures which are outlined for processing meat in glass jars.

Process 1/2 pint and pint jars for 100 minutes at:

10 psi - weighted gauge

11 psi - dial gauge

NOTE Canning fish in quart jars differs slightly.

Canning Fish in Quart Jars

When using quart sized jars, more time is required to heat the product thoroughly. Heat the canner on high for 20 minutes until steam comes through vent pipe in a steady stream. Allow the steam to escape for 10 minutes to vent the canner. The total time it takes to heat and vent the canner filled with quart jars should never be less than 30 minutes. The total time may be more than 30 minutes, especially if you have tightly packed jars, cold fish, or a larger sized canner. After you close the vent and bring the canner up to the recommended pressure and process containers:

Fish in quart jars - 160 minutes at:

10 psi - weighted gauge

11 psi - dial gauge

Canning Fish in Cans

Fresh or frozen fish can be used, thaw frozen fish in the refrigerator. Prepare fish using general cooking procedures: bleed and gut fish immediately after catching. Make sure you remove gills. Remove the head, tail, fins and scales.

You can leave bones in salmon and herring as they will soften during processing and storage. Remove the bones from halibut, when in doubt remove the bones. Cut fish into fillets or chunks which are best suited for the jar or can that you are using. The skin may be left on or off. Fillets may be rolled for packing. Salmon, trout, mullet, herring are oily fish so no oil is needed, however lean fish like halibut or cod will benefit from additional fat or oil.

Cans and lids: 1 pound (size: 301 x 408) or 1/2 pound (size: 307 x 200.25), also called Alaska salmon cans. According to University of Alaska in Fairbanks 25 pounds of fish as caught will fill 12, 1-pound cans or 24, 1/2-pound cans.

Follow procedure for canning meats in can, however note that fish are subjected to different (longer) processing times.

Process one pound cans (301 x 408) for 115 minutes at:

10 psi - weighted gauge

11 psi - dial gauge

Process half pound cans (307 x 200.25) for 95 minutes at:

10 psi - weighted gauge

11 psi - dial gauge

Canning Vegetables

Vegetables are low-acid foods and are subject to the same regulations as meat, poultry and fish. As vegetables grow in soil they usually contain large numbers of microorganisms. As explained earlier, the soil is the major carrier of Cl.botulinum spores. Vegetables are always washed but that removes only a part of the microorganisms and soil. The next step, known as blanching removes, kills or inactivates the majority of microorganisms present in vegetables. However, the ones that pose the highest security risk; Cl.botulinum survive as bacterial spores. Vegetables are low-acid food and as such will not prevent Cl. botulinum spores from germinating and producing toxin so they must be dealt with similarly to meats. Vegetables must be submitted to 240-250° F, 116-121° C heat treatment like all other low-acid foods in order to kill Cl.botulinum spores. High temperature thermal process often adversely affects delicate textured food like vegetables so commercial producers acidify the product to below pH 4.6. That allows them to process vegetables at pasteurization temperature. Look at the products in a supermarket; most food, for example, different types of pickles are acidified with vinegar in order to process them at lower temperature. For example, pH of cucumbers varies from 5.1-5.7, but pH of canned dill pickles is 3.2-3.5. Low-acid products acidified recipes are designed by the processing authority and approved by the FDA. However, the United Stated Department of Agriculture Bulletin 539 list many vegetable recipes that may be safely canned at home. All information in this book applies to both, vegetables and meat products and that includes equipment, processing steps and testing methods. The table below lists some common fruits and vegetables according to their pH. Acidity of foods depends upon many factors such as variety, maturity and growing conditions of the product. For these reasons, the pH of food is usually within a range of values.

Vegetables must be cleaned by soaking in water, spray washing or both. Then they are peeled, trimmed, and the large ones are reduced in size to make them suitable for packing. Next comes blanching. Blanching is a cooking process wherein the food substance, usually a vegetable or fruit, is plunged into hot water (close but below boiling point) for a few minutes only and plunged into iced water or placed under cold running water to stop the cooking process. Blanching liberates air and other gases which are present in cells of fruits and vegetables. If they are not removed prior to sealing, the air trapped in vegetables will be released into the headspace and will affect heat transfer, cause product oxidation and even internal corrosion of the containers. Blanching reduces the amounts of microorganisms and pesticides, improves the washing process and softens the skin for peeling. It also de-activates some of the enzymes that might affect the flavor, colour and texture of the product.

Cooling Containers

The thermally processed container should be cooled without delay to prevent the growth of thermophillic bacteria. As explained in the microbiology section, thermophillic bacteria like to grow at 122-150° F (50-66° C). It is very likely that thermophillic bacterial spores will survive thermal treatment. When the temperature inside the can drops down to (122-150° F 50-66° C), they will encounter favorable conditions to grow. For that reason commercial producers cool containers as fast as possible to about 95° F (35° C). However, a rapid depressurization of the canner and introducing cold water induces a great strain on a container which still remains under high pressure. This leads to a great pressure differential between the canner and the inside of the container and results in the following problems:

The contents of the glass jar will boil over through the still soft sealing compound. There will be less product inside, though the product will be fine and safe, as the sealant will reseal the lid when the pressure drops again. However, a stuck food particle may prevent the seal.

Food boil over.

Introducing cold water will shatter the hot jar due to thermal shock.

The high pressure inside the metal can will strain the seams and the ends of the can may buckle. What is worse is that the seam can be compromised and might not seal itself again, creating a safety risk. Smaller cans are usually not susceptible to this problem but any can from No. 3 (404 x 414) and bigger will buckle due to the large surface area.

Content loss due to boil over.

Commercial packers solve this problem by injecting compressed air first, and then introducing cold cooling water. The compressed air maintains the pressure inside of the canner at a level comparable with the pressure inside the container, and cold water lowers the temperature. This simple procedure requires large and expensive canners known as ìretortsî and such equipment is beyond the reach of a hobbyist. However, pressure cooling protects jars from breaking and cans from buckling.

Cooling at Home

There is a significant difference between commercial and home cooling processes.

Glass Jars. Home pressure canners have no means for injecting compressed air and introducing cold water. There is no other practical solution but to wait for the canner to depressurize by itself, which usually takes 30-45 minutes. Then the jars are taken out and left for cooling. Any short period growth of thermophillic bacteria will not result in any noticeable spoilage, but may decrease the shelf life of the product.

Jars are at a disadvantage as they face a thermal shock. Placing a hot jar in cold water will crack the glass. The glass jars are usually left undisturbed in the air for 12 hours to cool by themselves. However, there is a safety benefit in allowing the glass jars to cool by themselves; this fact is well documented in laboratory research studies. From 930 Bulletin Home Canning Processes for Low Acid Foods:

"These tests show that when foods are home canned in glass jars the long cooling periods required contribute significantly to the lethal value of processes. With vegetables in pint jars the sterilizing value of the cooling period averaged 50% of the total. In quart jars an average of 36 percent of the process value was contributed by the cooling period. In No. 2 and No. 2.5 tin cans the corresponding averages were 15 and 11 percent, respectively. Relatively high values of cooling periods for glass packs not, however, lead to generally shorter processes as compared with packs in tins. The exhaust given the latter before sealing resulted in higher initial temperatures which tended to balance the sterilizing value of the cooling period for processes in glass containers."

Metal Cans. It is possible to cool metal cans when using home pressure canners. Manufacturers specifically prohibit removing regulators from the steam vent pipe to drop the pressure rapidly in order to protect themselves from possible lawsuits. We all know the case when the lady spilled hot coffee over herself at McDonalds, took the company to court and was awarded 20 million dollars. Imagine manufacturers allowing people to remove steam pressure regulators from pressure canners. There will be ten new cases every day. Somehow, 70 years ago, the pressure canners were equipped with pet-cocks and home owners were gradually releasing pressure without injuring themselves. Well, we are a computerized society today, so we cannot handle simple manual tasks anymore.

Cooling procedure from the past: If canning in tin cans - with No. 3 cans, let pressure return to zero, the same as for glass jars, before opening pet-cock. With smaller cans, the pet-cock can be opened gradually without waiting for the canner to cool and pressure return to zero. Open canner as soon as all steam has been released. Take cans out of canner and cool at once in clean, cold water, until luke warm.

If the above procedure was performed and the cans were removed, their ends should be buckled due to the high pressure inside. This testifies that the cans were sealed properly and are tight. As they cool down pressure will fall, a vacuum will form and the lid will become slightly concave.

Left-pressurized can, right-can with vacuum inside.

Cooling with Air

Cooling cans with an air-fan at room temperature is a waste of time as air is such a poor cooling medium. After cooling with water for 60-240 min, commercially produced cans were cooled in 32-42° F (0-6° C) air for at least 12 hours. When the ambient temperature is low (outside), cooling cans in the air will be effective.

Most likely after thermal process, the canner will be left alone to depressurize and then the jars will be removed and placed on a towel in an area without much draft. Then, they will be left overnight to cool, form a vacuum and create a strong seal. Metal cans can follow the same procedure, however, they can be moved around and placed in a drafty area. They are stronger and the seal is well formed by now. There is a considerable advantage in a slow home canning process. The lack of cooling is offset by the additional processing time that the containers are submitted to. The long depressurizing step is nothing else as the additional heating step which starts at 240° F (118° C) and continues to about 160° F (72° C). It corresponds to a temperature range of slow-barbecue and may be considered an extra cooking time. This adds considerable safety to a home canning process.

Summing it up: even though you could depressurize the canner faster, please follow the manufacturers guidelines and wait until the pressure canner depressurizes to "0". However, once the canner is fully depressurized, we don't see any harm in immersing metal cans in cold water to drop the temperature to 95° F (35° C).