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The many ways of food preservation & processing.

Since the beginning of time, people have looked for ways to preserve food. They have looked for ways to store food for the long winter. They have looked for ways to save food gathered in times of plenty so that it could be used when food was scarce.

Of course, we have no records of how or when the first discoveries about food preservation were made. Perhaps hungry hunters ate berries that had dried on a bush or dried-up grapes f rom a grapevine. They liked the taste of the berries and took some home. Later, people learned how to dry the fresh berries and grapes by spreading them in the sun. People noticed that some foods could be dried over a fire and that the smoke preserved the foods. By chance people may have left some foods in a cool part of a cave or out in the snow. They saw that these cold or frozen foods lasted longer than fresh foods. They discovered that the salt found neat salt springs or along the seashore kept food from spoiling. Cooking also provided away of preserving foods for a short time. In these ways, people learned how to protect foods against the effects of time.

Later, people learned to tame animals rather than to hunt wild game. They learned to grow crops rather than to search for wild plants. They gave up their wandering life and built homes. They learned to make cheese and butter from the milk of their herbs and to make wine from the grapes they grow. They found that when wine soured, it became vine gat, which could be used to preserve some foods. They found that spices improved the taste of food. New ways of preserving food were added to their store of knowledge. But people still could not plan for the time when a crop might fail.

What Makes

Food Spoil?

Food can spoil, or decay, for several reasons. Much decay is caused by molds, which attack many kinds of food. Molds look like fuzzy growths on the surface of the food. They may be blue, green, brown, or black. You may have seen mold on fruit or bread.

Bacteria are tiny one-celled living organisms. They are too small to be seen without a microscope, but they also spoil many foods.

A third cause of spoilage is the action of enzymes. Enzymes are chemicals formed in living cells to help the cells carry on their life processes. Some enzymes continue their work after the cell is dead and destroy it, thus causing spoilage.

Some food-processing methods kill bacteria and molds, or at least keep them from growing. Other processes use certain bacteria or molds to preserve foods and give them special flavours. Have you even eaten Roquefort cheese or blue cheese? They are made with one of these molds. The taste of pickles and olives may depend on the growth of particular bacteria. Fruit juice maybe fermented by yeast to produce wine, which in turn may be changed into vinegar by certain bacteria.

Fresh foods will not keep one without spoiling. Foods must also be treated so they can be transported from the places where they are grown. Many processes have been developed to treat raw foods so that they may be preserved, or kept from spoilage or injury. These processes are canning, freezing, drying, pickling, spicing, sweetening, salting, smoking and preserving with chemicals.


The answers to the search for a better way to preserve foods grew out of the needs of an army at war. Toward the end of the 18th century, French soldiers suffered from a lack of food. Napoleon Bonaparte was greatly concerned with the health of his army and navy. The problem was not too little food, but that the food spoiled while d was being shipped and stored. Everywhere there was disease caused by spoiled food. In 1795 the French Government offered a prize of 12,000 francs to anyone who could find away to preserve food better.

Nicholas Appert (1750-1841), a French candymaker and chef, had long struggled with the problem of food spoilage. For years he had experimented in a simple kitchen with only a few tools. Finally his hard work paid off. In 1804 he successfully preserved food in sealed glass containers. Appert won the money prize and the admiration of the scientists of his day.

In canning, different types of foods must be cooked for different lengths of time. Most vegetables, meats, fish, chicken and dairy products have a low acid content. These need a longer cooking time than do fruits and other high-acid foods. To shorten the cooking time, low-acid foods are placed in huge containers that act as pressure cookers.

The steam under pressure raises the temperature until it is hotter than boiling water. High acid foods need cooking for only a short time in boiling water at a temperature of 100oC (212 F). Apples, which have a great deal of acid, can be made sterile, or free from bacteria, by heating them 10 to 15 minutes in boiling water. Peaches, which contain less acid, take 20 to 30 minutes of heating in boiling water.

But the time needed for cooking depends on more than just the amount of acid in the food. The cooking time will also be affected by the way the food is prepared, the size of the tin can, and the temperature of the food when it goes into the 3 can.

The science of canning is exact. For example, when whole-kernel corn at 60oc (140 F) is put into a number can, it takes 65 minutes of cooking at 115oC (240oF) to be sterile. Cream-style corn takes 160 minutes at the same cooking temperature. It takes longer because heat does not go into the thick cream-style liquid as easily as it goes into the watery brine used for whole-kernel corn.

Refrigeration and


From early times people have known that cold helps preserve food. The first refrigerators were probably caves with ice in them. In warmer climates, people stored food in a hole in the ground or in a cellar.

The development of the business of packaging frozen foods is credited to Clarence Birdseye (1886-1956). From 1912 to 1916, Birdseye was on a fur-trading expedition to Labrador, in eastern Canada. While there, he observed that quickly frozen fish tasted good and seemed fresh when it was thawed. He became interested in frozen foods, and for some time he experimented with the freezing of rabbits and fish. In 1924 he took part in forming a company that began quick-freezing various foods on a commercial scale. The early days of the business were not easy because in the 1920's not many homes in the United States and Canada had electric refrigerators. This meant that frozen foods could not be stored at home. When home freezers became available after World War-II, the frozen-food business boomed.

Cool Storage

The first of the two chief ways of preserving food with cold is cool storage, or refrigeration. This process uses temperatures just above freezing 0 to 2oC (32 to 35oF). Home refrigerators have these temperatures. This method will keep foods from spoiling for some time. But bacteria and molds will grow slowly, and after a while they will spoil the food.

Refrigeration makes R possible to get fresh food to markets when the food is produced a long distance away from the market or when doos eipwna in a very short period of time. For example, fruits and vegetables ripen in the southern part of the United States while snow is still on the ground in the northern states of Canada. The foods are picked ripe and are sent north by refrigerated railway cars or trucks. Milk, butter, and eggs all depend on refrigeration for distribution, storage, and marketing. So do yogurt and many cheeses.

Meat is transported all over the world in refrigerated ships, truck, and railway cars. For example, large amounts of meat are sent to Europe in refrigerated ships from Argentina, Australia, Canada and the United States. First, the animals are killed in slaughterhouse, and the meat is dressed or prepared by butchers. Then it is stored in large, cold rooms until it is shipped to market. When the meat reaches stores in your neighbourhood the stores continue to keep it under refrigerations until it is sold.


The second way to preserve food with cold is called freezing. This process generally uses temperatures between 18 and 10oC and (0 and-40oF). Freezing does not sterilize food, but the extreme cold stops the growth or spoilage organisms and greatly shows enzyme activity. Food that is kept frozen will not spoil. But it may spoil when thawed because living spoilage organisms are still present. Freezing generally preserves the fresh colour, flavour, and texture of fruits, vegetables, fish, meat and poultry better than any other method of food preservation known today.

Some fresh foods do not freeze well. Among them are tomatoes, cabbages, bananas, sliced or whole avocados, pears and some shellfish.

Drying Foods

Drying is one of the oldest methods of preserving foods. It is still the most common food-preservation process in the world.

The bacteria and molds that spoils fresh foods cannot multiply or grow without water. The heat used in the process of drying foods drives out the water in the foods by evaporation. Properly dried foods do not spoil.

Nearly all fruits, vegetables, meats, fish, eggs and milk can be dried. Dried foods take up less space and weigh less than other kinds of food. They also are easier to transport. To prepare dried foods for meals, people simply add the water that was removed when the foods were dried.

The two main ways of drying foods are sun-drying and dehydration, or mechanical drying. Sun-drying is the simpler of the two methods. The sun furnishes the heat and the wind currents carry the moisture-laden air away from the fruit. But sun-drying can be done only in those parts of the world where the days are long and sunny and where there is no rainfall in the season when the fruits are ripe. A rainfall before the fruit dried would spoil the fruit. Sun-drying takes a long time.

Chemical Preservatives

Food manufacturers use many chemicals to help preserve food. Some chemicals are used to slow the process of oxidation. These are useful in preventing fats from becoming rancid. Other chemicals destroy or prevent the growth of bacteria and other organisms. Still others are used to delay the sprouting of vegetables such as potatoes and carrots. And some are important because they help prevent the loss of valuable vitamins.

A few chemical preservatives also add food value to a product. The fatty acids that prevent mold from growing in foods have an important food value. Frozen fruits are kept from turning dark by adding vitamin `C'.

Other Means of

Food Preservation

Among the methods that have been known since ancient times are fermentation, sugaring, salt curing, and smoking.


The fermentation of grapes and other fruits to produce alcoholic drinks has been described in the earliest writings. The alcohol formed by the yeast preserves the wine as long as the container is kept closed. If air is allowed in the container, vinegar bacteria will spoil the wine. These bacteria feed on the alcohol and turn it into acetic acid. Sugar and salt, jams, jellies, preserves and marmalades are preserved by sugar. The sugar that is most commonly used is glucose, although some manufacturers are beginning to use fructose. A large amount of sugar in food inhibits, or slows, the growth of food-spoiling bacteria.

Dry salting and the pickling of meats and fish in brine have been practiced since before 2000 B.C. The product to be preserved was covered with dry salt or kept in a very strong salt solution until it was ready to be used.


After being cured or salted, many meats are smoked. Certain chemicals from the smoke are left on the meat. These chemicals help kill bacteria and give a pleasant taste to the meat.

New Methods

of Preservation

Ultraviolet light, which is part of the light coming from the sun, will kill spoilage organisms. Since the amount of ultraviolet light that the sun gives off is not enough to kill the organisms quickly, scientists have made special lamps that give off ultraviolet light. The light from these lamps can kill spoilage organisms on smooth surfaces or on foods that can be spread out in a thin layer. But since the light cannot go deeply into the food, food that either is thick or has an uneven surface cannot be made germ-free.


The radiation from radio-active materials has been used to serialize foods. This method is not completely successful because it causes odd tastes and smells. But it has been demonstrated that irradiation can prevent sprouting of stored potatoes and other vegetables. This prolongs their storage quality and availability to the consumer.


This is a new and still expensive process. Fresh food is quickly frozen and placed in a chamber from which all the air is removed, creating a vacuum. Because of the vacuum, the frozen moisture in the food turns into water vapour without melting. The water vapour is pumped out of the vacuum chamber as fast as forms, leaving the food with very little moisture. A piece of fruits treated by this process looks very much like fresh fruit, but it is very dry and porous (has tiny holes that will let in water). When ready for the table, freeze-dried foods look like fresh foods.

Food Processing Plants

Some food-processing plants are open only during the part of the year when the fruits or vegetables they process become ripe. Some plants are very small, while others have thousands of people working in them. Many things must be known before setting up a plant. How much of the raw material will be available.

Most food-processing plants try to process many different crops that ripen at different times. In this way, the plants can be kept open and working as long as possible each year. Cleanliness is important if the food is to be germ-free. A good supply of water is necessary. Waste must be disposed of safely. Thus you see that before a plant is built much must be known about the town, the country around it, the crops, the people, and the water and sewage. It is also important to know whether the product can be sold at a profit after the cost of producing and marketing. Today thousands of foods products from processors all around the world await us on the shelves of our food stores. Food processing and preservation have made it possible for us to have healthful and tasty foods all the year.
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Author:Ahsan, Sohail
Publication:Economic Review
Date:Aug 1, 1995
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