This article is a quick overview of different methods of food preservation that can be used by preppers, including: boiling water canning, pressure canning, freezing, drying, vacuum bags, salting, pickling, jams and jellies. When using any method of home food preservation, be sure to follow the directions and recipes closely. Be aware that bacteria can grow if improper methods are used, spoiling the food and even endangering health. As always, you should not rely on only one source of information. Do some research before you use any method of food preservation; be well-informed and use your own good judgment.
Bacteria grow well in damp and warm conditions, but they can survive refrigeration, freezing, boiling, and drying. Complete sterilization of food would kill all bacteria and all bacterial spores (a dormant form of the bacteria that is much more difficult to kill). Most home methods of food preservation don’t really kill all bacteria, they simply prevent bacterial growth. When you store dried beans, rice, nuts, seeds, and similar foods, you preserve the food by keeping it dry. There are bacteria in the food, but they can’t multiply without water. Then, when you cook the dried food, you kill the few bacteria that were present. Salting food is a method of drying. Bacteria cannot grow in salt because the salt draws water away from the bacteria. Even jams and jellies are in a sense “dry” because sugar also draws water away from bacteria. At about 50% sugar concentration, bacteria cannot grow.
Similar thinking applies to foods that are preserved without drying. In pickling, the acid from vinegar prevents bacterial growth. Refrigeration slows the growth of some bacteria and prevents the growth of other bacteria. Freezing stops all bacterial growth, but does not kill all bacteria. About the only method of home food preservation that kills bacteria and spores is pressure canning, which combines heat with pressure to obtain temperatures well above the boiling point. Boiling water canning (no use of pressure) does not have sufficient temperatures to kill all bacterial spores, so a certain level of acidity is also needed in the food.
There are two types of home canning: boiling water canning and pressure canning. The former uses simpler and less expensive equipment. But the recipes for the canned foods must have a certain level of acidity. Boiling kills all bacteria, but not bacterial spores. In particular, boiling does NOT kill botulism spores. Acidity in the canned food will prevent the spores from leaving dormancy and growing to dangerous levels.
Pressure canning allows a wider range of foods to be canned. The high pressure allows the water to reach a higher temperature. At ordinary pressure, water will only reach about 212 degrees F. At higher pressures, the water will reach a higher temperature (240 to 250 degrees F), sufficient to kill bacterial spores. Only pressure canning can be used for low acid vegetables, meat, and poultry. The disadvantage to pressure canning is that the equipment needed is more expensive, and if it is not done correctly, botulism can grow in the low-acid canned foods. In particular, adjustments need to be made if you are pressure canning at higher altitudes.
Any food that is frozen will keep indefinitely, as long as the temperature is held consistently at or below zero degrees F. The main issue with keeping food frozen for a long period of time is quality. Bacteria are not killed by freezing, but they cannot grow. Just as with drying, freezing denies bacteria the water that they need for growth. However, as soon as you begin to thaw the food, the bacteria can resume growing.
If you thaw frozen foods at room temperature, the bacterial growth can be quick enough to spoil the food or to endanger health. So it is always better to thaw frozen foods in the refrigerator. The second best approach to thawing is to thaw the food, while still sealed in a plastic bag, in a cold water bath. Change the water every half hour, and refrigerate as soon as it is thaw. This method thaws food faster, and keeps the temperature lower, so that bacteria cannot grow.
Certain foods are particularly good at growing bacteria, such as eggs and raw hamburger. Always thaw these foods at refrigerator temperatures. It is a good idea to have three thermometers in the kitchen: one in the freezer, one in the refrigerator, and a digital meat thermometer for foods being thawed or cooked. The freezer temperature should be kept at or below zero degrees F. The refrigerator temperature should be between 30 and 40 degrees F. And if you are thawing food on the counter, use the cold water technique, and make sure the water stays cold.
One approach to limiting bacterial growth during thawing is to cook the food prior to freezing. Cooking the food kills most of the bacteria. When raw foods are thawed, the starting amount of bacteria is high, and so the bacteria can grow to dangerous levels more quickly. When cooked foods are thawed, the starting amount of bacteria is low, and so it takes longer for the bacteria to spoil the food.
Certain foods don’t freeze well. Mayonnaise does not survive freezing. Mayo is an emulsion. The process of freezing and thawing takes the ingredients out of emulsion, so you end up with an unpalatable mess of liquids and solids. Anything made with mayo, such as coleslaw or potato salad, will not freeze well.
Dried foods store well: dry beans, peas, lentils, chickpeas, rice, wheat berries, pasta, dehydrated potato flakes, rolled oats, raisins, and more. All these foods keep well because they are dry. For grains such as wheat, the whole grains (the ‘berries’ as they are called) keep better than the flour. The berries have less surface area on which bacteria can grow. However, whole grains have oils in their bran that can go rancid after a number of months in storage. The same is true for nuts and seeds. The high oil content means that the food will not store as well as a dry food with low fat content, such as beans or rice.
For foods that have some oil content, like whole grains, nuts, and seeds, a lower temperature will slow rancidity. Keep dried foods well sealed, so that they do not absorb moisture from the air. Add a packet of silica gel (10 grams) to each 5 gallon sealed container. But also try to keep the stored foods somewhere cool, such as a basement. Cooler temperatures extend the shelf-life of dry foods, even if the temperature is above refrigerator temperatures.
You can dry your own foods in a commercial home food drier, or in a solar oven. If you grow your own grains, beans, nuts, or seeds, you will probably need a way to dry them. Cooking the seeds or nuts in an oven of course will also dry them. But you can’t use that approach for every food. You can also dry fruits or vegetables in a home food drier — but I’m not certain how long this type of dried food will keep without refrigeration.
Almost any food can be sealed in a vacuum bag for better storage life. This approach is very effective for frozen meat, poultry, and fish. The absence of air protects against freezer burn, and helps to maintain the quality of the food for longer storage. I have a small Foodsaver vacuum sealer for use in storing dry foods, like soy nuts, and for freezing foods that might be kept for many months in the freezer before use. When you vacuum seal a dried food, you don’t have to worry about the food absorbing moisture from the air in the container. Also, there is much less oxygen in the container; oxygen makes food go bad sooner. It is not so much a question of bacterial growth, as it is food quality. A vacuum sealer is a useful tool for prepping, but it doesn’t suffice to preserve any foods by itself. You have to use it with another food storage method, such as freezing or drying.
Salting, Curing, Smoking
I’m going to mention salting, as well as curing and smoking, for food preservation only briefly. It is difficult for the individual consumer to use this type of food preservation method inexpensively and safely. In this article, How to Salt Fish, the different problems associated with salting fish as a method of food preservation are discussed. If it is not done correctly, bacterial growth is very likely, and the food can easily become a danger to your health.
Curing and smoking meats yourself is also problematic. Nitrates and nitrites are often used as a preservative in cured meats. This “provides protection against the growth of botulism-producing organisms, acts to retard rancidity and stabilizes the flavor of the cured meat.” (Curing and Smoking). However, nitrates and nitrites are highly toxic and must be used with great caution. You also need a smokehouse for smoking your own meats.
By comparison, pickling is a relatively easy and inexpensive method of home food preservation. The acidity in the food is obtained by adding vinegar (e.g. pickles), or by fermenting (e.g. sauerkraut). “There must be a minimum, uniform level of acid throughout the mixed product to prevent the growth of botulinum bacteria.” (HFP) Follow the recipe carefully, and don’t change any of the ingredients or proportions. Otherwise, you might have too little acid, and botulism would be a risk.
Even though this type of preservation of food is relatively easy, it is also limited. Only certain foods can be pickled and stored. I think of this option as providing condiments, rather than staple foods.
Jams and Jellies
As I mentioned already, this method of preserving food uses sugar to prevent the growth of bacteria. Often pectin is used to keep the mixture from separating, because a separated layer might allow bacteria to grow. Unless you are making a ‘freezer jam’, you will need to use a boiling method of canning (no pressure cooker needed) to kill bacteria. The high sugar content does not kill bacteria; it only prevents their continued growth.
What is the difference between jams, jellies, preserves, conserves, and marmalades? See this detailed explanation. And here is a set of instructions for making numerous different types of jellied products.
Your main protein and carbohydrate staple foods are probably going to be dried foods. In addition to staples like pasta, rice, and legumes, you can buy a wide array of commercially freeze-dried foods that have an excellent shelf-life. Freeze-drying removes more water, and so the food keeps longer.
Your best source of stored dietary fat is vegetable oil. Highly refined oils will generally keep for about two years without refrigeration. Canola oil has the best balance of essential fatty acids (omega-6 and omega-3), and it keeps well. Soybean oil is also a good choice.
Freezing food long-term is an excellent approach. You can freeze almost any food, and it will keep safely for an indefinite period of time as long as it is kept at or below zero degrees F. This is the best method for storing meat, poultry, fish, and cheese. However, you can only fit so much food in a freezer. Consider getting a separate chest freezer for an ample supply of high quality protein, as well as some additional dietary fat.
Resources for further reading:
National Center for Home Food Preservation
Prudent Food Storage: Q and A
USDA, Fact Sheets/Safe Food Handling/Freezing and Food Safety