VIII The Diverse Uses of Processed Sweetpotatoes
Compared with other root and tuber crops, sweetpotatoes are employed in a much wider range of uses. These include starch, followed by processed foods, brewing and feed. Both for processed foods and brewing, new highly functional varieties of sweetpotatoes, along with associated products, offer great promise.
Most starch made from sweetpotatoes is used for producing isomerized saccharides as a sweetener for soft drinks, as well as for harusame noodles, dried sweetpotato starch noodle. Recently, development work has been conducted on reimen (cold Korean noodles), with the aim of utilizing sweetpotatoes. Noodles characterized by transparency and unique elasticity are now ready for the market.
Starch dregs generated from starch production are difficult to process. One current study is being conducted to determine whether dregs can be used to produce biodegradable plastic materials or no-calorie sweeteners.
(1) About 9% of the sweetpotatoes produced in Japan are used for processed foods, about half the corresponding percentage for potatoes, but the processed foods involved are extremely diverse. The two most common are hoshiimo (dried slices of steamed sweetpotatoes), followed by confectionery. In southern Kyushu, sweetpotatoes are being increasingly used for frozen foods such as diced sweetpotatoes and semi-processed foods such as flakes. One new processing-oriented market for sweetpotatoes is beverages and powder. As with flake production, powder production enables the nutrients and colorful pigments of sweetpotatoes to be effectively utilized; also, the powder can undergo secondary processing with ease. With these features, sweetpotato-based powders are expected to be used extensively for breads, cookies and noodles. In addition, roast sweetpotatoes and daigakuimo (fried sweetpotato coated with sugar syrup and sesame) have long been favored by the Japanese. Recently, however, frozen processed foods imported from China have gained significant market share.
(2) Use of sweetpotatoes for pigments is also attracting considerable attention. "Ayamurasaki," released in fiscal 1995, is the world's first sweetpotato variety developed especially for pigment production. It was developed through joint research between the Kyushu National Agricultural Experiment Station and Saneigen FFI, a top pigment maker. Although the earlier "Yamakawamurasaki" variety produced a deep purple pigment, it was defective in terms of yield. "Ayamurasaki" contains several times more pigment than "Yamakawamurasaki," and can also be cultivated easily.
Many studies have already been conducted on the extraction of pigments, development of new paste and flake products, utilization of extract dregs for shochu production, use of starch, and high-yield cultivation of "Ayamurasaki." One finding thus far is that brandy-flavored Shochu can be produced from the "Ayamurasaki." There are considerable hopes for the commercial prospects of this new variety.
○ Changes in use for processed foods
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Note: |
Data from the Upland Farming Promotion Section, MAFF. |
○ Sweetpotato paste
A paste suitable for confectioneries and snack foods is produced by steaming potatoes, then straining and freezing them. The most suitable variety for paste is "Kokei No. 14," which undergoes minimal blackening or discoloration after cooking. By using pigmented varieties, colorful pastes of orange and purple can be produced. Paste is shipped after being processed as follows: potato selection, washing and peeling (manual operation), cutting (to the size of daigakuimo), steaming (20 minutes), straining (removal of fiber), sugar adjustment (malt syrup), and freezing. Confectioners then use the shipped paste to form yokan bars and manju buns. To produce a high-quality paste, it is necessary to use high-quality sweetpotatoes.
3. Shochu and other alcoholic beverages
(1) Imojochu is a popular drink with a history of at least 500 years. It is characterized by its attractive aroma and flavor. Captain Jorje Alvares, a Portuguese sailor who stayed in the Yamakawa port in Satsuma in 1545, recorded in his book "Japan Report" that Oraka (distilled spirits, shochu) was imbibed by many people of all social standings. Saisho Shimazu, the 28th feudal lord of Satsuma, was famous for his imojochu production in the last days of the Tokugawa government. Indeed, he developed Shochu production into one of the major industries in Satsuma.
(2) Imojochu is made from several different varieties of sweetpotato, including "Koganesengan," "Shirosatsuma," and "Shiroyutaka." Use of the highest-quality materials is essential. The actual production process for imojochu involves four steps: koji (malted rice) production, first fermentation, second fermentation, and distillation. The first step, koji production, requires about 40 hours, during which polished rice must be steamed and cooled, and koji-kin (Aspergillus oryzae) added. During the first fermentation, water and yeast are added to the koji and the resulting mix is allowed to ferment for about 1 week. During the second fermentation, the mix - now known as moromi (unrefined "sake") - is combined with sweetpotatoes (already steamed, cooled and mashed) and water. This product is fermented for 9-10 days, then distilled, stored, and matured.
(3) Unlike "a class A spirit," imojochu is produced by distilling moromi through the traditional simple distillation method. Recently, however, new attempts have been made to use sweetpotatoes for beer and wine. Studies are being conducted on utilizing the dregs formed during fermentation as a source of energy.
4. Other Uses for Processed Foods
Although sweetpotato leaves are hardly used for food, an attempt is now underway to produce a commercial tea from them. To do so, it is necessary to obtain varieties that have leaves suitable for tea production. As we noted earlier, the history of sweetpotatoes is closely linked to processing practices, specifically to developments in plant breeding. In the years to come, as new and unique sweetpotato varieties are developed, we can look forward to the introduction of an ongoing array of revolutionary processed foods.