Key Technical Points of Indoor Secondary Fermentation for Agaricus bisporus Production

The compost that has undergone outdoor pre-fermentation is moved indoors, and through artificial temperature and air control, the compost is sterilized and fermented under specific environmental conditions, further enhancing the specificity and selectivity of the compost, so that the compost is fermented into a substrate more suitable for mushroom growth. This process is called indoor secondary fermentation.

(1) Principle: Secondary fermentation is a biochemical reaction process in which the activities of various types of thermophilic microorganisms promote changes in the physical and chemical properties of the compost. Secondary fermentation can be divided into two stages. Stage one: raise the pile temperature to 57-60degC and hold for 6-8 hours. This stage is called pasteurization. Its effects are: first, at high temperature, the enzymes of most pathogenic fungi are thermally inactivated, especially respiratory enzymes, which are denatured and cause death; second, high temperature causes the proteins of some pests (eggs, larvae, adults) to be heat-denatured and coagulated, causing death; third, within this temperature range, it provides environmental conditions for the survival and activity of beneficial thermophilic microorganisms. Stage two: ventilate to lower the compost temperature in the mushroom house to 48-52degC and hold for 5-7 days. The air temperature in the mushroom house must not be lower than 45degC. Its effects are: first, due to ventilation and cooling, the oxygen supply conditions for microorganisms are improved, promoting the massive proliferation of thermophilic microbial groups (including thermophilic bacteria, actinomycetes, and thermophilic molds); second, the pathogenic bacteria remaining from the previous stage of secondary fermentation are further killed.

(2) Forms: According to the conditions for rural mushroom cultivation in China, there are two relatively effective forms of secondary fermentation. One is to use the mushroom house bed frames for secondary fermentation: loosen the compost that has undergone outdoor pre-fermentation and move it onto the mushroom house bed frames (do not place compost on the bottom and top layers), then seal the mushroom house and heat it. The other is to use vegetable pipe sheds or bamboo sheds shaped like vegetable pipe sheds: build a simple layer of bed frames 15 cm above the ground on both sides inside the shed. The bed frames are 1.5 m wide, and the central walkway is 1.2 m wide (a small flatbed cart can pass through). Place the compost that has undergone outdoor pre-fermentation on the bed frames, pile it to a height of 0.8-1 m and a width of 1.5 m, make some holes in the middle of the pile, then seal and heat it for secondary fermentation. After secondary fermentation is completed, move the compost onto the mushroom house bed frames. Although this form adds one extra procedure, the temperature of the compost during secondary fermentation is easy to control, the secondary fermentation quality is high, and it saves energy.

(3) Operating steps. a. Timing of loading: after the third turning of the outdoor secondary fermentation, after two days, the compost temperature can rise to its highest, generally around 70degC; at this time, loading can begin. b. Piling and bedding: the compost that has undergone outdoor pre-fermentation must be loosened before it can be moved into the secondary fermentation room. After the compost is moved onto the bed frames, pay attention to the pile shape; make it as high as possible, and keep the surrounding pile edges straight and level. Only in this way can the compost better retain heat and ferment evenly. c. Heating: after the compost is loaded into the room, close the doors and windows tightly and seal all ventilation openings of the mushroom house. The best time to start heating is after the compost temperature has already risen automatically following loading; generally, start heating 6-8 hours after loading. After the compost temperature rises to 57-60degC, hold for 6-8 hours, then ventilate appropriately to cool down. After the compost temperature drops to 48-52degC, maintain for 5-7 days. During the period when the compost is held at temperature, the room temperature must not be lower than 45degC, and ventilation should be carried out regularly during this stage to prevent oxygen deficiency in the secondary fermentation room from inhibiting the reproduction and growth of beneficial microorganisms. After secondary fermentation is completed, open the doors and windows promptly; when cooling, open the doors and windows from small to large. d. Adjusting compost moisture: if steam is used for secondary fermentation, the moisture content of the compost after secondary fermentation will be somewhat higher. Therefore, during outdoor fermentation, the compost can be kept appropriately on the dry side, with a moisture content of 60%. If a coal stove is used for direct heating, because the dry heat produced by the coal stove will cause the compost to lose more water through evaporation, after secondary fermentation is completed, spray some clear lime water at pH 8-8.5 on the surface of the compost to adjust the moisture content of the compost.

(4) Standards for the compost after secondary fermentation is completed: the color is dark coffee to dark brown, fully soft, the straw has relatively strong elasticity, when the compost is held in the hand the manure does not stick to the hand, and there is a relatively strong compost aroma, no ammonia odor, a large amount of white actinomycetes and light gray humic molds, a moisture content of about 65%, pH 7.2-7.5, and no pests or miscellaneous bacteria.

(5) Safety must be paid attention to during secondary fermentation: during secondary fermentation of the compost, two people should be on duty at the same time to prevent accidents caused by excessively high temperature in the mushroom house or too much carbon monoxide when adding coal. Coal stoves should be placed properly in the mushroom house to prevent fires.