Processing Method for Low-Sugar Sweet Potato Preserves

1. Raw material selection: Sweet potato varieties are classified into many types, such as those with good sweetness and those with high starch content, and the colors of the skin and flesh vary widely, such as red, white, yellow, purple, gray, etc. For processing sweet potato preserves, varieties with high starch content and low moisture should be selected, especially fresh, smooth, plump sweet potato tubers free of insect damage and rotten skin, with yellow-fleshed or red-fleshed varieties being preferred.

2. Washing and peeling: Rinse the selected tubers clean with water, peel off the skin with a stainless steel knife, and cut into 5 cm thick slices. To prevent the tubers from discoloring, during peeling and slicing, the peeled raw material must be placed in a 1%-1.5% salt solution or a 0.1%-0.5% citric acid solution for color-protection treatment. After slicing, to improve the boiling resistance of the raw material, quickly place the slices in an equal weight of 0.2%-0.3% calcium chloride solution, add 0.15% potassium sorbate, soak for about 10 hours, then remove, rinse clean with tap water, and drain off the surface water for later use.

3. Sugar processing and vacuum treatment: First prepare a 45%-50% sugar solution (the weight of the sugar solution being 55%-60% of the sweet potato slices), bring to a boil, then add the sweet potato slices, spices, citric acid, etc., bring to a boil again, and maintain for 5-8 minutes to cook the slices thoroughly. When the temperature drops to about 50°C, pour into a vacuum filter, carry out vacuum treatment for 30-40 minutes at a vacuum degree of 60-66.7 kpa, then pour the sweet potato slices together with the sugar solution into a vat or non-iron container and sugar-soak for 24 hours.

4. Baking: First remove the sweet potato slices, rinse the surface sugar solution with warm water, and drain dry. Evenly arrange the drained, sugar solution-removed sweet potato slices on baking trays, send into the drying room, bake at 50°C-60°C for about 5 hours, then raise the temperature to 65°C and bake for 8-10 hours, swap the baking trays so the product dries evenly, then raise the temperature to 75°C and bake until the preserves are no longer sticky to the touch, soft and chewy, with a moisture content of 18%-20%. During baking, to facilitate drying of the product, ventilate and remove moisture in a timely manner, generally 2-3 times during the drying process, each time about 15 minutes.

5. Softening, trimming, packaging: Place the preserves in a room at about 24°C to soften for 72 hours, remove substandard products such as those that are overcooked, shriveled, or severely browned, trim the preserves, then weigh and package them separately according to size and color, and they are finished products.