What are the key points for fresh-keeping processing of shiitake mushrooms for export?
I. Raw material selection
The raw materials must be fresh and of normal color. The mushroom caps must be intact in shape, the stems must be complete and unblemished, and the mushrooms must retain their elegant form as when growing naturally. The flesh must be thick, the cap edges must be evenly inrolled, the partial veil must be unbroken or slightly open, and the caps must not have opened. The cap diameter must be no less than 38 mm. Free of pests and diseases, off-odors, and soil impurities.
II. Raw material handling and cold storage
1. Precooling and moisture removal of raw materials To maintain good freshness and color of the raw materials, fresh mushrooms must be promptly placed in a cold store for precooling and temperature reduction after harvest. According to equipment performance and the moisture content of the fresh mushrooms, maintain an appropriate precooling temperature and moderate dehydration rate, and through precooling and moisture removal, meet export requirements. If the forced-air cooling method is used, control the cold store temperature between 1°C and 3°C, keep the core temperature of the fresh mushrooms at 2°C to 4°C, and reduce the moisture content of the fresh mushrooms to 75%-80%.
Carry out screening or manual visual sorting. Grading usually adopts a three-grade system: large-grade mushrooms (L) with a cap diameter of 55 mm or more; medium-grade mushrooms (M) with a cap diameter between 45 mm and 55 mm; small-grade mushrooms (S) with a cap diameter between 38 mm and 45 mm. While grading the raw materials, inferior mushrooms should be removed, and after selection they should be promptly stored in cold storage. Where conditions permit, grading and sorting can be carried out in the cold store to ensure good quality of the fresh mushrooms.
3. Cold storage and fresh-keeping During cold storage, the temperature of the cold store directly affects the quality of the finished fresh mushrooms. If the cold store temperature is higher than 5°C, the fresh mushrooms can still continue metabolism, causing a decrease in freshness; if the cold storage temperature is lower than 0°C, the fresh mushrooms are prone to cold damage, resulting in water-soaked rot and deterioration. Therefore, during cold storage, the cold storage temperature must be strictly controlled between 1°C and 3°C.
III. Packaging and transport
The packaging containers for fresh-keeping shiitake mushrooms generally use rectangular plastic boxes with lids die-cast from foam plastic, with raised ridges around the lid edges to maintain a tight fit with the box opening. To ensure the quality of the fresh mushrooms, packaging materials and containers must not only be hygienic and non-toxic, but also heat-insulating and airtight, unaffected by the external environment, with strong cold-retention performance for a certain period of time, and able to keep the fresh mushrooms in a good low-temperature state.
Fresh mushroom packaging must be carried out in a clean and hygienic low-temperature room with no off-odors and a temperature no higher than 3°C
Packaging utensils and staff uniforms must be kept clean and hygienic and disinfected regularly. Packaging must be carried out before the confirmed export date. First, cut the fresh mushroom stems short, leaving about 25 cm, and package while cutting the stems; if the stems are cut too early, the cut surfaces of the stems will oxidize and brown, affecting appearance. The fresh mushrooms are placed in plastic film bags, mushrooms of the same grade are put into the bag, vacuum-sealed, and then packed into foam plastic boxes; the box openings are sealed and covered with double-wall corrugated cardboard boxes, and the cardboard box openings are sealed with tape. Packaged fresh-keeping shiitake mushrooms must be shipped promptly; export fresh mushrooms transported from the production area to the port must be transported in refrigerated trucks with strict control of the cold storage temperature.