The Processing of Potatoes for Food

Francis P. Griffiths.

Potatoes are grown in all parts of the country and are harvested in one place or another in each of the four seasons. Even in winter, from Florida and the lower Rio Grande Valley in Texas, we can get new potatoes. So, because potatoes are widely grown and easily available, until relatively recently there was little purpose in processing them.

Today, however, we process about 22 million bushels of the 300 million bushels of potatoes we produce for food each year. Potato chips use up 18 to 20 million bushels more, and other products account for 2 to 4 million bushels. We use normally an additional 2 million bushels for potato flour. About 20 million bushels of potatoes were dehydrated the last 2 years of the Second World War.

Why do we not process all the potatoes we do not eat fresh so that none will be wasted? Part of the answer is that processing serves one of two purposes : It makes for more convenient use, or it makes specialty products available. In times of war, dehydrated potatoes are important because dried, compressed, and packaged they take up much less space and weight in transportation and storage. In times of peace, the problems of preparing acceptable processed products are different, but even more numerous than under the necessities of war. Each product must meet with the approval of the American public. Is it better than the one it is meant to replace or at least as good? Will it save time, money, or effort? Is it attractive in appearance? Is it appetizing?

Such practical demands must be met if a new product is to succeed. If it competes with or replaces another made from a different vegetable or fruit, it must be as good as the old one preferably better.

Frozen prepared foods are an example of a new type of processed foods that combine availability and palatability with great savings of time.

Dried potatoes and canned potatoes meet the housewife's demands for less waste, more time saved, greater convenience. Both are successful products. Such specialties as shoestring and hash-brown potatoes, french-fries, and potato chips meet the requirements and are appetizing as well. Hence their success with the public, especially chips, which are the leading potato product.

DEHYDRATION OF POTATOES had grown considerably by the end of the First World War. In 1919, when the technique was still in its infancy, about 7 million pounds of dehydrated potatoes were produced. But because of limited technological information and failure to produce a top-quality product, the industry declined.

The Second World War gave it fresh impetus. But neither our technique of handling food nor our scientific and engineering knowledge of dehydration was sufficiently advanced to meet fully the large wartime demands. Dehydrated potatoes and other vegetables deteriorated rapidly in storage. We did, not know what caused the deterioration or how to prevent it. The Government set to work on those problems. Much valuable information was accumulated, but some of it came too late for use in the war. Although consumption of dehydrated food declined after the war, several companies have remained in the business, and research on the subject has continued. This continuation of production and research now provides a nucleus for effective orientation and expansion of the industry to meet the 1951 national defense needs.

Which potatoes are best suited for dehydration? First, the variety selected must be grown in a district and under conditions to which it is adapted and where it will give the best yields. The type that becomes white and mealy when cooked is preferred. Katandin in the East and Russet Burbank in the West are two of the best varieties for dehydration.

At the beginning of the Second World War, improper blanching (heating with steam) was a common fault in commercial. operations. Over-blanching of the high-density potatoes causes what is known as popcorn effect. The potato puffs up; each ball has a hard shell and a hollow center, so that it is excessively mushy when prepared for the table.

But under-blanching, or incomplete destruction of enzymes, causes potatoes to darken excessively during processing. Such improperly blanched potatoes are difficult to reconstitute, and they deteriorate rapidly in storage.

Why blanch potatoes before dehydration? Obviously, the potatoes are blanched to inactivate enzymes. But that answer disregards the even more important questions: Which enzymes are involved in the blanching process? What treatment can be used to eliminate the enzymes that are deleterious?

The role of each enzyme in producing the changes is not yet completely understood. Research, however, has developed a test for enzyme inactivation which defines proper blanching time a large forward step in the field of dehydration.

Factors that hasten deterioration are being isolated and methods of combating them developed. Storage tests have disclosed the harmful effects of high temperatures on the dried potatoes and other dehydrated vegetables. Treatment with sulfur dioxide, packing in containers with a gas such as carbon dioxide or nitrogen, or putting in the container a sort of auxiliary container holding a substance that will take up moisture ( called in-package desiccation) are being studied in relation to this problem. Already, by a combination of these techniques, deterioration has been reduced.

Treatment of fruits and vegetables with sulfur dioxide to prevent darkening has been known in this country for some time, but the public has viewed it with disfavor. Because technical data on its application were lacking, it was sometimes used without discrimination. The result was a food so unpalatable that the public rejected not only the food but the process as well. Used in proper amounts, sulfur dioxide is a valuable aid to dehydration. Potatoes require less sulfur dioxide than either carrots or cabbage. Application of 400 to 500 parts per million of sulfite markedly improves the color in dehydrated potatoes, as it keeps them from graying during dehydration. Moreover, it increases their ability to retain vitamin C and improves their storage quality. In proper application, sulfur dioxide leaves no unpleasant taste.

In-package desiccation of dehydrated food is a recent development, and a significant one. The method was adopted shortly before the end of the Second World War in new procurement specifications by the Army Quartermaster Corps. It is simple. By means of calcium oxide (lime) stored in the container in such a way that it does not come in contact with the food, the moisture content of the package is lowered from the 6 to 8 percent that is obtained by the usual dehydration methods to between 2.5 and 4 percent. The use of in-package desiccation extends by about sixfold the storage life of dehydrated potatoes at room temperature. The process may become important in any future Army procurement program for dehydrated food.