Sterilization of Shiitake Mushroom Logs

After bagging, sterilize them in an autoclave as soon as possible. There are two sterilization methods: atmospheric pressure steam sterilization and high pressure steam sterilization. When using high pressure steam sterilization, sterilize at 0.15MPa pressure for 2 hours. When using atmospheric pressure steam sterilization, raise the temperature to 100℃ within 3-5 hours. If sterilizing 3000-5000 bags at a time, maintain the temperature for 20-24 hours. After achieving sterilization, anneal the bags, open the plastic film, and handle the bags while they are still hot. Wear cotton gloves to carefully inspect the bags. If any cracks or tears are found, tape should be applied while they are still hot. Handle with care to prevent the bags from being torn or getting wet from rain. Stack them properly in the cooling room. The following points should be noted during sterilization:

(1) Timely Sterilization

The culture medium contains a large number of microorganisms. If it is not sterilized in time after watering, it is prone to spoilage. After filling, it should be sterilized immediately.

(2) Properly Stack Bags: Bags should be stacked vertically, forming a straight line to ensure smooth airflow from bottom to top. If possible, use a transfer basket, placing one bag at a time (loading from the periphery towards the center to prevent the basket from scraping the bags). The bags can also be placed in baskets for sterilization, avoiding compression and deformation while ensuring thorough sterilization. Handle the bags gently when loading them into the sterilizer. If you encounter a "water bag" or an overly soft bag, remove it and return it to the previous cycle.

(3) Exhaust Cold Air: Whether using high-pressure or atmospheric-pressure sterilization, all cold air must be exhausted; otherwise, false pressure will be created, leading to incomplete sterilization. During high-pressure sterilization, exhaust cold air when the steam pressure reaches 0.05 MPa, and close the exhaust vent after exhausting all cold air. During atmospheric-pressure sterilization, open the exhaust vent of the sterilizer, and wait until the discharged steam reaches 98°C, then close the exhaust vent after 10 minutes.

(4) Temperature Indicators

① High-Pressure Sterilization: Maintain a steam pressure of 0.15 MPa and a temperature of 126℃ in the sterilizer for 2 hours.

② Atmospheric Pressure Sterilization: After the bags enter the sterilizing chamber, immediately apply high heat to raise the temperature to 100℃ in 3-5 hours. The sterilization time depends on the number of bags: approximately 3000 bags require 20 hours, 5000 bags require 24 hours, and over 8000 bags require over 36 hours. After the sterilization time is reached, stop the heat and let it sit for 6 hours to ensure proper sterilization before, during, and after, preventing a "large start, small finish, and loose middle." Note that slow heating can easily cause acidification of the culture medium; if the water in the sterilizer is insufficient, add hot water above 80℃.

(5) Bag Unloading and Handling: Before unloading the bags, loosen the screws on the door of the sterilizing chamber and pull the door slightly outward to create a gap, allowing steam to escape slowly. If the door is opened suddenly, hot air will rush out of the chamber, and cold air will rush in, easily causing the bags to rupture. When the temperature drops below 70℃, cotton gloves can be worn to remove the bags while they are still hot. The bags should not be removed from the chamber too cold; they must be removed while still hot, otherwise it will hinder the formation of the substrate bags. Handle the bags gently when loading and unloading them. If the bag ends are found to be loose or cracks appear on the surface, immediately tie the bag ends securely with thread and seal any cracks with adhesive tape. The unloaded bags should be transported to the cooling chamber on a cart lined with burlap sacks to prevent puncturing.