Detailed Explanation of the Technical Method for Brewing Baijiu from Sweet Potato

Brewing is the process of using starch as a raw material and, through the action of fermenting microorganisms, converting starch and sugar into alcohol. In China, in addition to grains (rice, sorghum), sweet potato is mainly used as a brewing raw material. When sweet potato is used as the raw material for brewing, its starch utilization rate and liquor yield are higher than those of other grains, while the cost of the liquor is low.

1. Process flow: making jiuyao (starter culture) -- raw material treatment -- fermentation -- distillation -- adjustment of alcohol content -- storage

2. Key points of process operation:

① Making jiuyao: jiuyao can be divided into two types, black and white. White jiuyao is prepared from the smartweed herb and rice bran or rice flour as raw materials. In addition to the above raw materials, the preparation of black jiuyao also requires the addition of other medicinal materials such as dried tangerine peel, Sichuan pepper, licorice, cinnamon, and Atractylodes lancea. The medicinal materials used to prepare jiuyao vary from place to place, ranging from more than a dozen kinds to as many as a hundred. Because these medicinal materials contain phosphorus, potassium, magnesium, nitrogen, and growth stimulants, they are beneficial to the reproduction of the microbial strains. Jiuyao contains saccharifying bacteria and yeast, which can first saccharify starchy raw materials and then ferment them into alcohol.

Taking white jiuyao as an example, the preparation method is as follows: its raw materials are prepared at a ratio of 19 kg rice flour, 7 kg water, 500 g aged jiuyao, and 150 g spicy smartweed. During production, first mix the rice flour, smartweed powder, and water evenly, place the mixture in a wooden box 100 cm long, 60 cm wide, and 6-7 cm high, spread it flat, press it tight, then cover it with a reed mat and press it firmly. Use a knife to cut it into small pieces 2-3 cm square, place them on a roller and roll them so that the square corners are rounded off. Then move them into a shallow wooden tray, add finely ground aged jiuyao and shake so that it adheres to the surface of the dough pieces. Then place the prepared dough pieces in a qu tray, move them into a culture room, and keep them warm for cultivation for 1-2 days, after which white mycelium and conidia grow. During this period, turn them over once from top to bottom to facilitate the reproduction of the microbial strains. At this time, if the temperature is not high, there is no need to open the windows for ventilation. After 3-4 days of cultivation, cover the qu trays with cloth and expose them to the sun; after about 6 days they can be fully dried, then stored in a dry place for use at any time.

② Raw material treatment: after washing fresh sweet potatoes, cut them into pieces, mix them into 4%-9% crushed rice husk, and heat and steam them to promote the gelatinization and expansion of starch so as to facilitate saccharification. When steaming, first add 1/3 of the water to the pot. After boiling, place the material in batches onto the bamboo rack of the steaming vessel, and when steam rises, add the second layer. If the steam is uneven, add some moistened crushed husk at the places where the steam is weak. After all the material has been added, cover with the pot lid and steam for 30-40 minutes, until cooked but not mushy. Then take it out and spread it on a cooling mat, turn the material over and break up the clumps. During spreading and cooling, it must be done quickly; after cooling to about 38 degrees Celsius, pile it into a small heap and carry out the first mixing with jiuyao. When the product temperature drops to about 35 degrees Celsius, carry out the second mixing with jiuyao (1 kg of jiuyao can be used per 100 kg of fresh sweet potato), and mix the jiuyao thoroughly and evenly. When the temperature drops to 27-28 degrees Celsius, it can be gathered into a heap, with a heap height of about 15 cm; the heap height varies with temperature changes (slightly thinner when the temperature is high, slightly thicker when the temperature is low). Then sprinkle a small amount of jiuyao on the surface. At this time the heap temperature is about 24 degrees Celsius, and the surroundings of the heap must be kept warm. Keep it warm for about 10 hours; when the temperature rises to 30 degrees Celsius, remove part of the insulating material to prevent the temperature from continuing to rise. If it exceeds 35 degrees Celsius, turn and mix once. After another 10 hours or so, when the sweet potato material is completely saccharified and has a fresh fragrance, it can proceed to further fermentation.

③ Fermentation: spread out the saccharified raw material to cool, add an equal amount of spent mash and mix evenly, and when it has cooled to 24 degrees Celsius, put it into the pit, spread it flat, and press it firm. A layer of spent mash or rice husk can be sprinkled on top, and then it can be sealed well with yellow mud. If a wooden lid or thick cardboard is used to cover it tightly, it is more convenient for collecting waste gas. Leave a 3 cm square exhaust hole in the center of the pit so as to collect carbon dioxide for comprehensive utilization. The pit entry temperature is about 22 degrees Celsius. After that, check 1-2 times every day. After 3-4 days the temperature rises, alcohol fermentation becomes vigorous, and when the temperature begins to decline, it can be taken out for distillation. Under normal conditions, complete fermentation can be achieved in about 1 week. Whether fermentation is complete can be determined according to temperature and exhaust conditions. After the raw material is put into the pit for fermentation for 8 hours, the temperature rises slowly. When it rises to 35-37 degrees Celsius, it is maintained at a constant temperature for a period of time, and then begins to decline. When the product temperature drops to about 25 degrees Celsius, fermentation is complete. If checked by exhaust conditions, after the raw material has been in the pit for 24 hours, place your hand over the exhaust hole and you can feel hot air discharging from it. After that, the hot air gradually increases. When fermentation is at its most vigorous, hot air can be felt discharging at a distance of 30-60 cm from the exhaust hole. When the exhaust volume decreases to the point that no exhaust can be felt, it indicates that fermentation is completely finished.

④ Distillation: during distillation of the liquor, whether to add rice husk depends on the looseness of the fermented mash. Sweet potato mash generally has high viscosity, so an appropriate amount of rice husk should be added to avoid uneven steam distribution during distillation. The procedure for loading the mash for distillation is basically the same as that for loading materials for steaming. After covering the lid, open the cold water. Because the distilled liquor varies in quality, the head and tail fractions should be stored separately, otherwise the quality will be affected. The head and tail liquors can be further distilled to produce liquor. In order to improve the flavor and aroma, newly distilled baijiu must be aged. In order to remove a small amount of impurities and off-odors from the liquor, sometimes 0.01%-0.02% potassium permanganate and 0.5% activated carbon are added, left to stand for 48 hours, and then filtered. However, it must be noted that the amount of potassium permanganate must not be too much, otherwise it is harmful to human health.

⑤ Adjustment of alcohol content: in order to make the alcohol content of the liquor conform to the market @#@136@#@ standard, manual adjustment of alcohol content should be carried out. If the concentration is insufficient, an appropriate amount of alcohol can be added; conversely, if the concentration is too high, it needs to be diluted with water. After the alcohol content is adjusted, it can be put into containers for storage.