Sweetpotatoes for Food and Feed

P. R. Dawson.

In the United States, sweetpotatoes are used primarily for human food. Some culls and other unmarketable subgrade potatoes are fed to livestock, but such use is essentially a salvage measure.

Well over 90 percent of the sweet-potatoes used for food are prepared as needed from the fresh raw product and are stored, shipped, distributed, and purchased by the ultimate consumer in this form. Because of the bulk and perishability of sweetpotatoes, many efforts have been made to process them into food products that could be stored and distributed without loss and prepared for the table without waste and with little time and effort. However, canning is the only process in general use today for the preservation of sweet-potatoes.

SWEETPOTATOES have been canned commercially for more than 50 years. Around 100,000 cases were packed in 1899 for the United States as a whole. Production rose to a peak of some 769,000 cases in 1925, and then dropped, reaching a low of 159,000 cases in 1933. The financial depression contributed to this recession, but another factor was the stiffened competition with fresh sweetpotatoes, which were becoming available in better quality and distribution over a longer season. The solid or mash packs, the only styles in use up to that time, were not satisfactory substitutes for the fresh vegetable.

After 1933 the production of canned sweetpotatoes again took an upward trend, until in 1940 a pack of some 800,000 cases for the first time exceeded the previous high of 1925. Vacuum packing of whole small sweet-potatoes of the Jersey type, which could be so processed without objectionable softening, had been introduced in the Middle Atlantic States. The vacuum-packed product was more attractive to consumers who favored the drier, or more mealy-fleshed, sweetpotatoes. In the late 1930's the sirup pack was introduced. Varieties which have a greater tendency to soften in processing than do the Jersey types retain their shape and firmness when canned in sirup. The development made possible a very attractive pack of the Porto Rico variety of sweetpotato widely grown in the Deep South. It found ready consumer favor and gave impetus to expansion of sweetpotato canning in the South Central and the Southeastern States.

With the added impetus of defense and lend-lease demands, the output of canned sweetpotatoes more than doubled in 1941. Production dropped back abruptly in 1942, and, while progressively increasing in 1943 and 1944, was kept below its 1941 level by wartime restrictions on sugar and tin plate. In 1945, however, 2,260,000 cases set a new high, which was topped by the 1946 production of more than 3 million cases.

Greater activity of canners in the Deep South, particularly in Louisiana, was responsible for the recent increases in the production of canned sweetpotatoes. At one time Maryland and Virginia were the leading sweetpotato canners. Mississippi put up about 21 percent of the national pack in 1919,but in the succeeding 12 years dropped to 7 to 10 percent and in 1935 and 1037 to 2 to 3 percent. In the record season of 1946, Louisiana alone accounted for nearly 40 percent of the total production reported by the National Canners' Association.

The solid or mash packs have been largely displaced by the whole pack in sirup and the vacuum pack.

The 1946 pack was greater than the demand and resulted in a surplus that was difficult to move. The inferior quality of some of it gave the industry a setback the following season. However, with disposition of the surplus and more widespread adoption of improved practices in selection of raw material and in preparation and processing, canned sweetpotatoes are finding a steadily expanding outlet. Some of the newer varieties and selections of sweetpotatoes offer promise for further improvement of the canned product. Solution of some processing problems which still hamper output of a uniformly high-quality product should expand the market still further.

DEHYDRATED sweetpotatoes made an important contribution to the supply of dehydrated foods for our Armed Forces in the Second World War. From 1942 through 1945 more than 4 million bushels were processed to produce close to 40 million pounds of dry product.

For many years there had been recurrent efforts to prepare a stable dehydrated sweetpotato product. Preservation of sweetpotatoes for home use by simple drying procedures is common in rural sections in China, Japan, and other countries where the crop is commonly grown. Small-scale drying was rather common in our Southern States before modern storage methods made it possible to keep the fresh roots in good condition for longer periods after harvest. However, the products from simple drying of sweetpotatoes without cooking or blanching leave much to be desired with respect to retention of color and flavor and reabsorption of Moisture when prepared for the table.

A number of patents were granted on processes for dehydrating sweet-potatoes before 1900. In 1899 the South Carolina Agricultural Experiment Station undertook investigations to improve the dehydration process. Attempts to commercialize dehydrated sweetpotato products, however, met with little success until the Second World War. Then modern dehydration of sweetpotatoes for food use became a substantial enterprise.

Early in 1942 a Louisiana enterprise which had pioneered in the dehydration of sweetpotatoes for stock feed submitted to the Army Quartermaster Corps sample lots of sweetpotatoes dehydrated for food use by the latest procedures. A substantial order followed. The plant was converted to food dehydration and was in full production in the 1942-43 season. By 1944, 20 or more plants were dehydrating sweet-potatoes under Army contracts. Close to 40 million pounds were turned out from 1942 to 1945 and more than 4 million bushels of sweetpotatoes were processed.

There was some hope that dehydrated sweetpotatoes might find an outlet in civilian consumption after the war ended. Some producers placed limited quantities on the market; but not much consumer demand developed. Production dropped off abruptly in 1946 and since then it has become negligible. Most of the wartime plants have been dismantled or have been converted to canning. Apparently, they have found it difficult to compete with good canned sweetpotatoes where a stable packaged product, easily prepared for the table, is desired.

There is opportunity for further improvement in the quality of dehydrated sweetpotatoes by use of new varieties of superior quality for drying and by further improvement in processing methods. However, in 1951 there was relatively little activity in this field.

FLOURS OR MEALS prepared by grinding and screening the dehydrated sweetpotatoes have recurrent interest as supplements to wheat flour in bakery products. From time to time attempts have been made to manufacture and exploit them commercially, but, as a rule, the production was only experimental and lasted but a short time when carried to the commercial scale.

From 1900 to 1906 Henry S. Morris, of Philadelphia, manufactured a flour by grinding and bolting sliced and dried sweetpotatoes. During the First World War sweetpotato flour was used to some extent, but the products were not such as to encourage production after the emergency had passed.

In 1919 the Bureau of Chemistry prepared flour from sweetpotatoes by tree flake process which had been used for white potatoes. The steamed potatoes were dried in a steam-heated double-drum drier and the resulting flakes were ground into flour. The results were unsatisfactory. Some years later, light-colored flours of high starch content were prepared experimentally from sliced air-dried sweetpotatoes, and in further experiments stable flours were obtained by grinding sweetpotatoes that had been dehydrated after a treatment with a cell-plasmolyzing agent and pressing out the excess water and solubles. It was thought that such products might be useful in brewing or in baking and in the manufacture of adhesives, but no commercial development followed.

For several years just before and during the Second World War a flour or meal prepared from dried sweet-potatoes was marketed in small quantities by a Texas concern. Its manufacture was discontinued when no demand developed.

Most of the sweetpotato flours produced up to this time have been prepared from potatoes that were dried without precooking or blanching. Such products deteriorate rather rapidly in flavor on keeping.

Toward the end of the Second World War some interest developed in the production of a flour by grinding and screening dehydrated sweetpotatoes prepared by the improved blanching and drying procedures used in supplying the Armed Services. One processor in Louisiana made and distributed such a flour for a short time. It was superior in flavor and keeping quality and found some use as an ice-cream stabilizer when stabilizers previously used were in short supply. It appeared to offer promise as an ingredient of pie fillings, puddings, and cakes. However, the producer suspended operations in 1947 and the flour disappeared from the market.

A NOVEL LINE of processed food products from sweetpotatoes has been developed experimentally by L. M. Ware and associates at the Alabama Agricultural Experiment Station. The sweetpotatoes are baked slowly until fully cooked, with maximum conversion of starch to maltose and dextrins, then peeled and pulped to a puree. The puree, with admixture of other ingredients where desired, is extruded onto trays and dried, with a final toasting in a bake oven. The product has a moisture content of only 2 to 3 percent. The size of the extruded strips, the character of added ingredients, such as coconut, sugar, and orange, and the degree of toasting are varied to produce confections of the taffy type, snacks, breakfast foods, and the like. The products are very attractive in appearance and flavor. Limited quantities, produced on a pilot-plant scale, have received favorable response when marketed on a trial basis.

Another product, a precooked flour, is prepared by grinding the dried extruded puree in a buhrstone mill. It makes a highly satisfactory ingredient of cakes, cookies, puddings, and icings. Milk shakes containing it were well received at a soda fountain in Auburn.

The Alabama Experiment Station products have not yet been exploited commercially. However, they seem promising if the process can be adapted to economical operation on a commercial scale.

Encouraging consumer reactions to several of the products were obtained in Nation-wide acceptance tests conducted in 1949-50 with the cooperation of the Bureau of Agricultural Economics.

Sweetpotato confections prepared by processes similar to those used in the preparation of candied or crystallized fruits are said to be popular in some South American countries, but have not been exploited to any extent in the United States.