Soybean is an annual herb of dicotyledonous plant class, Leguminosae and soybean genus, with a height of 30-90cm. Stem stout, erect, densely brownish hirsute.

Leaves usually have 3 leaflets, stipules with veins, yellow pubescence, petioles about 220 cm long, leaflets are wide ovate, papery, racemes short with few flowers, long with many flowers. The total pedicel usually has 5-8 sessile and crowded flowers, the bracts are lanceolate, strigose, bracteoles are lanceolate, the setae are pressed, the calyx is lanceolate, the flowers are purple, lavender or white, the base is valved, and the wing is castor shaped. The fruit is plump, slightly curved, drooping, yellow green, densely covered with brown yellow long hair. There are 2-5 seeds, elliptic, nearly spherical, smooth testa, light green, yellow, brown, black and other colors. The flowering period of soybean is from June to July, and the fruiting period is from July to September.

Soybean handling process

1、Raw material processing

The raw soybeans harvested from all over the country, which qualified through grade inspection will become raw soybeans. After that, soybeans will be selected carefully to remove inclusions and neat grains. Then beans will be put into 30kg paperbags for storage. Soybeans should be stored at low temperature warehouse that with 15℃ temperature and 60% humidity , otherwise the soybeans are easily to deteriorate thus cause big losses.

2、soybean washing and soaking

The selected soybeans are cleaned with a bean washing machine to remove the sand, dust and organic substances attached to the surface. The purpose of immersion is to make the water be absorbed into the seed of raw soybeans, soften the tissue and be easy to steam and cook, so that the natto bacteria can easily use the soybean ingredients. The moderate soaking needs to be calculated by the weight ratio. When the weight reaches 2.3-2.4 times of the original beans, cutting off the soybean can see that two seeds expand to almost no space. The soaking time varies according to the soybean variety and size, but the most influential is the water temperature, which needs to be soaked for 23-24 hours at 10℃, 17-18 hours at 15℃, and 13-14 hours at 20℃, Immersion is required for 7-8 hours at 25℃ water temperature, and special attention shall be paid, in case of over immersion in summer. Although the following cooking process can kill the mixed bacteria, its residual metabolites will affect the growth of natto bacteria, which can completely inhibit the propagation of natto bacteria when it is severe. Therefore, it is necessary to take low temperature to inhibit the growth of mixed bacteria as much as possible. The ideal situation is to select the water temperature below 10℃ for soaking. When a small amount of production, the temperature can be controlled at 5℃ in the refrigerator for soaking, and the cooking can be carried out after about 24 hours. The length of soaking time can be judged according to the size, tissue status and water absorption of the beans. To determine the soaking time, 100 gram of soybean raw materials can be put into a small bag for soaking, taken out in a certain period of time, and weighed them after the moisture removed as much as possible.

3、steam and cook

The function of cooking is to kill the soil microorganism on the surface of soybeans, soften most of the tissues, and make the soluble components of seed and fruit soak into the surface of soybean skin. Therefore, after inoculation, natto bacteria is easy to absorb nutrients, while the enzyme in vitro of natto bacteria is easy to soak in and decompose soybean components. First, increase the pressure of the pressure cooker to about 5kg, then put the two bags of soaked soybeans into the cooking pot, lock the upper cover with the open bolt, open the drain valve and the exhaust valve, and then guide the boiler water vapor into the cooking pot through the steam piping. Once the drain pipe of the cooking pot is opened, the incoming water vapor first discharges the condensed water and the cooking juice produced by the soybean cooking to the outside, At this time, the water vapor is discharged. At this time, close the drain valve, close the exhaust valve, and the steam pressure will rise to 1.0-2.0 kgin 10-20 minutes after the exhaust valve is closed. Keep it for 30-40 minutes, and then close the steam valve. Wait for 10-15 minutes, the cooking is completed. After the cooking is completed, open the water distribution pipe and the exhaust pipe softly to see the steam, and then open the cover.

4、Inoculating natto

During the operation, the temperature is between 70℃-90 ℃, and the natto fungus is evenly attached to the surface of cooked soybean. This operation is called inoculation. 5cubic centimeters of soybean fungus liquid can be inoculated with a soybean sandbag. The soybean fungus liquid is the suspension of natto bean. There are about 100 million to 200 million spores in 1cubic centimeter. In terms of 100 million, there are about 4000 spores attached to 1 gram of cooked soybean, and about 1300 spores are on the surface of one soybean, To evenly distribute 5cubic centimeter bacteria on a sand bag, it is necessary to increase the sterilization water increments in advance, to cool the boiled drinking water to about 50℃, spray the two sandbags to spray wine, dilute to 2 kg, and use the kettle to spread the sterile water which is dissolved in 2.5 kg.

Phnix - soybean dryer Technology

The 6p drying and dehumidification integrated host is selected to be equipped with a drying room( 5.5 meters long*3 meters wide*2 meters high), which is equipped with 6 material trucks, each with a size of 1.2 meters long, 1 meter wide and 1.7 meter high. It is divided into 12 layers of grid pallets. Each truck is loaded with 150kgs, and one batch is loaded with 600kgs. The temperature range is set about 50℃to 60℃,time setting is 20 hours, and the final water content reaches 12%. The drying process is over.