Food Preservation Methods




Techniques for preserving food have been around for many tens of thousands of years. The ability to store reserves of food has been one of the keys to the survival of the human species, especially in areas in which the ability to hunt was determined and limited by the seasons.

Fresh food is a privilege not enjoyed by everybody in the world. Many people live for extended periods of time on food which has been preserved in one way of another. Modern methods of food preservation can ensure that food will be fit to eat many years after it was processed.

Food preservation serves two main functions. A) to delay the development of  bacteria in a product and/or to destroy certain forms of  undesirable bacteria  and B) to completely destroy and prevent the development of bacteria in a product.

In the first example we are doing two things. We are extending the “shelf life” of a product and/or we may be both extending the shelf life and eradicating certain  micro organisms that are destroyed at relatively low pasteurization  temperatures.

In the second category we are ensuring that there will be no future bacterial development within the product and thus the product may be good to eat many years after the date of manufacture.

Here are the main forms of food preservation:

1. Sterilization

2. Pasteurization

3. Dehydration

4. Salination

5. Concentration

6. Refrigeration (including freezing)

7. Preservation

8. Picking

Now lets define the categories one by one:

Sterilization. Sterilization is basically the use of radioactive energy to destroy all forms of microscopic life in a food source or any form of food wrapping or container. Sterilization can be used to increase shelf life of products that will not be packed in sterile conditions or to preserve foods that need to be maintained in sterile conditions for extended periods of time. This method is also used to sterilize materials such as spices and herbs that are to be used in manufacturing sensitive products such as cheeses and eggs. If this method were not used the risk of cross contamination would be much higher.

Sterilization is the subject of much public concern. People feel that the long term effects of radiation usage in foods may be damaging to health. Much debate exists in this area.

Pasteurization. Pasteurization is the process in which a food is heated to a specific temperature and them put into a container to separate it from the environment. Milk is the example of pasteurization which is known to most people. Cattle and sheep are sometimes carriers of the Brucella Melitensis bacteria, also know as Maltese fever. This bacteria presents some very severe health risks for humans. The disease transmitted by the brucella bacteria is called Brucellosis. Brucella Melitensis is a very heat sensitive bacteria and is destroyed at a temperature of sixty five degrees centigrade. Milk is pasteurized in a plate pasteurizer and held at a temperature of seventy degrees centigrade for thirty seconds to make sure that all the bacteria are killed. The milk is then rapidly chilled to a temperature of two degrees centigrade to prevent the development of other forms of bacteria.

This method of food preservation includes canning and the bottling of liquids which do not contain preservatives.

Each type of food has it’s own temperature of pasteurization. In many cases the pasteurization temperature depends upon the effect that the manufacturer wants to attain for the food. For example, regular bottled orange juice is heated to ninety five degrees centigrade to kill off all micro organisms but “freshly squeezed” orange juice is only pasteurized to a temperature of seventy degrees centigrade because the manufacturer wants the taste to be less effected by the pasteurization process. This limited effect on the taste permits the manufacturer to market the orange juice as freshly squeezed.  The manufacturer  will take into consideration that the shelf life of this product will be less than that of bottled orange juice.

Dehydration. This process is use on vegetables, fruit, eggs, spices, and meat primarily. In this process the product is dried to a level of about five percent humidity.  At this hydration level bacteria will not be able to be active and will either die or become dormant. Traditional methods of dehydrating include sun drying, oven drying and smoking. Modern methods include spray drying, freeze drying, drum drying and other forms of drying.

Many type of foods need some preparation in order to undergo dehydration. This usually includes some form of slicing, cleaning or grinding.

Salination. Salination means the adding of salt to a product to destroy bacteria. The salt may be added directly in dry form or in a liquid salt solution (this form of preservation is called brining). Salt that is added directly has the effect of drying the product. Salted meats are often completely dry. Salting can also be used to extend the shelf  life of a product. In this method a relatively small amount of salt is spread on meat to delay the development od bacteria. Kosher law demands that meats be treated with salt after slaughter.

Concentration. This method of food preservation includes the making of jams and conserves. Many liquid foods can be concentrated. This means that the majority of the water content within the liquid is extracted usually by heating until the remaining substances within the retentate are so concentrated that bacteria will not survive in that concentration. the best example of concentrated liquid is honey. Honey is nearly always concentrated naturally by bees by the beating of their wings to a level of eighty Bx. any kind of extract can be concentrated as can any type of juice or syrup.

Refrigeration. This is the cooling of any type of food to a temperature at which the activity of bacteria will be curbed or completely stopped. Again, refrigeration to temperature of around four degrees centigrade will extend the shelf life and of food considerably. Food that is frozen can be kept for even longer periods of time. With freezing care must be taken because if kept frozen too long the freezing process can have an adverse effect upon the tissues of the food, especially meats. Refrigerated foods should be kept at a constant temperature of four degrees centigrade and frozen foods should be kept at a constant temperature of minus eighteen degrees centigrade. Freezing is the one form of food preservation that is considered a very good second best to fresh food. Test have shown that frozen foods, particularly vegetables, can contain as many or more nutrients as fresh produce because frozen food is frozen almost immediately after harvesting whereas fresh produce can be a week old or more before it hits the shops.

Preservation. Another way to prevent food from spoiling is to preserve it by using preservatives. Preservatives are chemical substances which when added to food or drink will prevent the development of bacteria within the food. Again, preservatives can be used in a variety of different ways. In salads, preservatives are used in small amounts to delay bacterial growth thus extending the shelf life of the product. In other methods of use preservatives are used in higher dosages to entirely halt bacterial development. Similarly to the use of radiation with food, the use of preservatives has come under attack by people who think that preservatives present a danger to health.

Pickling. Pickling is the preservation of food in an acid or salt based solution. In actual fact most pickling processes include a combination of salt, pepper, sugar and vinegar solution with added spices such as peppers, garlic and turmeric, all of which contribute to lowering the Ph of the solution into which the food is to be placed. The solution is boiled and the food is then added. Every type of food has it’s own pickling process. Some recipes require extended cooking and some only require that the food be brought to the boil inside the pickling solution. The food is jarred hot inside the boiling solution and stored. Pickling needs experience to do properly. Getting the process wrong may result in serious illness.

Pickling gives us the ability not only to preserve food but also to make food tasty and an interesting addition to almost any meal.