What issues should be noted in the export processing of fresh-keeping shiitake mushrooms?

I. Raw material selection

In the processing of fresh-keeping shiitake mushrooms, the first thing to note is the freshness of the raw materials, which is an important factor determining the quality of the finished fresh-keeping shiitake mushrooms. The raw materials must be fresh, and the color must be normal; secondly, the mushroom caps must be complete and round in shape, the stems must be intact, and the mushroom bodies must retain the graceful form of natural growth; the mushroom flesh must be thick, the edges of the caps must be neatly incurred, the partial veil unbroken or slightly open, and not fully opened; the cap diameter must be no less than 38 mm; and there must be no pests or diseases, off-odors, or soil impurities.

II. Raw material handling and cold storage

First, pre-cooling and moisture removal of the raw materials must be carried out. To maintain good freshness and color of the raw materials, fresh mushrooms should be promptly placed into cold storage for pre-cooling and temperature reduction after harvesting. According to equipment performance and the moisture content of the fresh mushrooms, the appropriate pre-cooling temperature and moderate dehydration rate should be controlled, and through pre-cooling and moisture removal, the export requirements should be met. If the forced-air cooling method is used, the cold storage temperature should be controlled between 1°C-3°C, the core temperature of the fresh mushrooms should be 2°C-4°C, and the moisture content of the fresh mushrooms should be reduced to 75%-80%. At room temperature, the methods of moisture removal by ventilation in a cool shaded place or by spreading the mushrooms out under sunlight should not be used.

Second, grading and selection of the raw materials. According to the requirements of foreign trade customers, grading is usually carried out by screening with grading sieves made of galvanized iron according to cap diameter, or by manual visual sorting. Grading usually adopts a three-tier system: large-grade mushrooms (L) with a cap diameter above 55 mm, medium-grade mushrooms (M) with a cap diameter between 45-55 mm, and small-grade mushrooms (S) with a cap diameter between 38-45 mm. While grading the raw materials, damaged, stem-detached, discolored, spotted, deformed, and substandard inferior mushrooms should be removed, and after selection they should be promptly put into cold storage. In areas with the necessary conditions, grading and selection can be carried out in cold storage to ensure the good quality of the fresh mushrooms.

Third, cold storage preservation should be carried out. During the cold storage period, the temperature of the cold storage warehouse directly affects the quality of the finished fresh mushrooms; therefore, the temperature of the cold storage warehouse during cold storage is extremely important. If the cold storage warehouse temperature is higher than 5°C, the fresh mushrooms can still continue metabolism, causing reduced freshness, aging of tissues, and eventually opening of the caps; if the cold storage temperature is lower than 0°C, the fresh mushrooms are prone to freeze damage, the mushroom bodies soften, and eventually water-soaked rot and deterioration occur, making them unfit even for consumption. Therefore, the cold storage temperature during the cold storage period must be strictly controlled between 1°C-3°C.

III. Packaging and transportation

The packaging of fresh-keeping shiitake mushrooms differs from the packaging of other products. To ensure the quality of the fresh mushrooms, the 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.

The packaging containers for fresh-keeping shiitake mushrooms generally use rectangular plastic boxes with lids die-cast from foamed plastic, with raised ridges around the edges of the lids to maintain a tight fit with the box opening. After the mushrooms are packed, the edges around the box opening are then sealed with transparent adhesive tape.

The packaging of fresh mushrooms must be carried out in a clean and hygienic low-temperature room with no off-odors and a temperature no higher than 3°C. The packaging utensils and the uniforms of the workers must be kept clean and hygienic and disinfected regularly. Non-staff personnel must not enter or leave the packaging area at will, in order to prevent the warehouse temperature from rising and the introduction of pathogens and debris that could contaminate the product.

Packaging must be carried out before the confirmed export date. First, the stems of the fresh mushrooms are cut short, leaving a length of about 25 cm, and packaging is carried out 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, with mushrooms of the same grade placed in the bag, vacuumed, and then packed into foamed plastic boxes; the box openings are bonded and sealed and then placed in double-corrugated cardboard boxes, with adhesive tape added to the box openings.

There are also cases where small packaging is used to hold the shiitake mushrooms. Small packaging usually uses small trays made of foamed plastic bags, with the fresh mushrooms in each tray arranged neatly, some with the gills facing outward, wrapped on the outside with a layer of cling film sealed airtight or vacuumed, and then placed into cardboard boxes, with adhesive tape added to the box openings. After packaging is completed, markings are made, and they are ready for shipment.

After packaging, fresh-keeping shiitake mushrooms must be shipped out 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 to prevent the temperature from rising, thereby ensuring the quality of the fresh mushrooms.

IV. Several issues to note in production

Most fresh-keeping shiitake mushrooms belong to artificially cultivated sawdust shiitake mushrooms rather than shiitake mushrooms cultivated on logs. In production, in order to inhibit the occurrence and harm of contaminating microorganisms, carbendazim or other fungicides are usually mixed into the nutrient material for cultivating shiitake mushrooms for mold prevention and sterilization, and the amount used should be strictly limited to the minimum range safe for the human body. During the shiitake mushroom cultivation and production process, a large amount of water must be sprayed every day. The water quality must be clean and clear, and must not carry microorganisms or metal substances harmful to the human body, so as to ensure that the fresh mushrooms are clean and hygienic. Like other mushrooms, shiitake mushrooms contain a large amount of water in the mushroom bodies, generally all above 90%. To maintain the quality of the finished product and shorten the moisture removal time, spraying water must be strictly prohibited one day before harvesting the fresh mushrooms.