I. Causes of occurrence
 
1. Incomplete sterilization
 
① When sterilizing at atmospheric pressure, the discharge of bacteria bottles (bags) in the sterilization pot is too dense, and the temperature rises too fast, and the cold air is not drained, resulting in false pressure. Mismatch between the boiler gas supply and the capacity of the sterilization pot and sterilized material; the temperature in the bags does not reach 100℃ within 4h after the boiler ignition. During the sterilization process, the temperature was not continuously maintained above 100°C by using steam sterilization on the boiler.
 
② When autoclaving, the sterilization pot is discharged too densely, the sterilization boiler pipeline is too long, and the pipeline insulation is insufficient; the cold air in the pipeline is not removed first, and the steam entering the pot is not saturated steam; the cold air is not removed cleanly.
 
③ Raw materials such as corn cob and large granular wood chips that do not easily eat through moisture are not pre-wetted in advance, and the mixing time should be extended, otherwise it is easy to have incomplete sterilization due to the inability to eat through moisture inside large granules.
 
④ The wheat grain soaking too wet, filler too loose can cause sterilization incomplete and cause endogenous contamination.
 
2. Inoculation contamination
 
Inoculation is done under the FFU laminar flow hood in the purification room of the assembly line, and the number of colonies of settling bacteria in the purification room is not frequently detected, the area does not reach the thousand grade standard, the aseptic operation is not strict, and the inoculation environment is not clean.
 
3. Inoculation quantity is not enough
 
Some bacteria mycelium growth is slow, the inoculum is not enough, the mycelium did not occupy the absolute advantage as soon as possible.
 
4. Infection in the germinating period
 
① Use liquid strain inoculation, when the inoculation gun is spraying liquid strain, splashing of bacterium liquid causes contamination from time to time; after inoculation, it is not cultured under purified air, which is easy to produce contamination.
 
② After inoculation placed in the culture library, the library purification is too low, resulting in contamination of mold with the exchange of internal and external gases.
 
③ use of poor quality bags, or in the bagging, handling process caused by bag breakage, culture 5 ~ 15d, there will be scattered spots on the surface of the material or around the bag.
 
Second, the prevention and control methods
 
1. The culture material should be fresh, dry, with reasonable formula, moderate water content, tight packing and tight sealing; raw materials such as corn cob, large particles of wood shavings that cannot easily eat through the water should be pre-wetted in advance, or extend the mixing time to prevent incomplete sterilization due to the internal impermeability of large particles; real-time monitoring of the sterilization process to ensure complete sterilization.
 
2. Strictly check the quality of strain and increase the amount of strain appropriately.
 
3. The whole process of inoculation should be aseptic, and the inoculated bags should be taken in and out gently to prevent the bags from being broken.
 
4. Do the environmental hygiene inside and outside the culture room and the mushroom place, and dispose the waste in time. The disinfectant used in the culture room should be rotated frequently to prevent the germs from becoming resistant to drugs.
 
5. Handle the miscellaneous bacteria in time when found in the culture process, check every 5~7d during the culture process to eliminate the miscellaneous bacteria at the stage of spot piece occurrence; the strains with particularly serious contamination should usually be destroyed immediately.
 
6. For old mushroom sheds infected with streptomycetes in the last season, you can also fumigate the cultivars with special chemicals before entering the sheds to prevent the re-occurrence of streptomycetes.