A Detailed Guide to Practical Techniques for Shiitake Mushroom Processing and Fresh-Keeping

When harvesting shiitake mushrooms, place them gently in plastic baskets without squeezing or deforming them, then remove impurities from the fruiting bodies, pick out damaged mushrooms, trim the base of the stems, and sort them according to cap size, thickness and moisture content, arranging them on bamboo blinds or reed mats in a ventilated place. They should be processed promptly; piling them together for a long time will reduce quality.

1. Drying shiitake mushrooms

(1) Sun-drying: For mushrooms to be sun-dried, stop spraying water directly on the fruiting bodies 2-3 days before harvest to avoid excessive moisture content in the fresh mushrooms. Harvest promptly when the fruiting bodies are 70-80% mature, the partial veil has just broken, and the cap edges curl inward in the shape of a copper gong. It is best to harvest on a sunny day; after harvest, use stainless steel scissors to trim the stem base, sort according to cap size, thickness and moisture content, spread them gill-side up on reed mats or bamboo blinds, and place them in sunlight to dry. Generally, about 3 days of drying is needed to reach full dryness. The sun-drying method for shiitake mushrooms is simple and low-cost, but in the early stage of sun-drying, enzymes and other active substances in the fruiting bodies cannot immediately lose their activity, and there is a certain "after-ripening" effect that affects commercial quality. On overcast and rainy days, it is difficult to sun-dry qualified commercial mushrooms. In addition, sun-dried shiitake mushrooms do not have as rich an aroma as oven-dried ones, which somewhat affects their commercial value.

(2) Oven-drying: Clean and trim freshly harvested shiitake mushrooms immediately, cut off the stem base, sort according to cap size and thickness, and spread them gill-side down on bamboo trays with mesh openings no smaller than 1 cm. First preheat the dryer to about 45°C to reduce the humidity inside the machine, then place the bamboo trays with the spread fresh mushrooms on the drying racks by category. Place small thick mushrooms and mushrooms with low moisture content on the upper layer of the rack, thin mushrooms and medium-sized caps on the middle layer, and large thick mushrooms or mushrooms with high moisture content on the lower layer. The temperature inside the machine gradually drops; the starting temperature for drying is 35°C for drier shiitake mushrooms and 30°C for wetter ones. At this time the fruiting bodies have high moisture content, and after heating, surface moisture evaporates rapidly. To accelerate moisture evaporation, fully open the air inlet and exhaust vent of the dryer to increase ventilation, discharge water vapor, help the upright gills become fixed, and prevent them from collapsing. At this stage the drying temperature should not be high, otherwise the fruiting bodies are prone to darkening or being steamed cooked. Water vapor should be discharged promptly to prevent free water from appearing on the mushroom surface, so as to avoid affecting the color and aroma of the shiitake mushrooms and to prevent difficulty in drying. During drying, raise the temperature by 5°C every 3 hours; when the drying temperature rises to 45°C, moisture evaporation from the fruiting bodies decreases, and at this point 1/3 of the air inlet and exhaust vent can be closed. When drying enters the fruiting body dehydration stage, after maintaining for 3 hours, open the chamber door and swap the upper and lower positions of the drying trays so that the fruiting bodies on each layer dry evenly. Thereafter, raise the temperature by 5°C every 1 hour; when the temperature rises to 50°C, close 1/2 of the air inlet and exhaust vent. When the temperature rises to 55°C, the gills and cap edges are completely dried, but the stems are not yet fully dry; at this point stop heating and let the drying temperature drop to about 35°C. Because the internal temperature of the mushrooms is now higher than the surface temperature, the diffusion of moisture from inside the mushrooms to the surface is accelerated. After 4 hours, reheat and dry again; when the temperature rises to 50-55°C, open 1/2 of the air inlet and exhaust vent, maintain for 3-4 hours, then close the air inlet and exhaust vent, control the drying temperature at 60°C, and maintain for 2 hours to reach full dryness.

(3) Combined sun-drying and oven-drying: After freshly harvested shiitake mushrooms are trimmed, spread them on bamboo trays and sun-dry them for 6-8 hours to initially dehydrate the fruiting bodies before oven-drying. This can reduce drying costs and also ensure the quality of the dried mushrooms.

(4) Storage of dried shiitake mushrooms: After drying, shiitake mushrooms have a moisture content below 13%; the stem breaks easily when gently gripped by hand and gives off a crisp sound. However, they should not be too dry, otherwise they break easily. Dried shiitake mushrooms readily absorb moisture and rehydrate, so they should be packed according to grade in double-layer large plastic bags with the bag openings sealed tightly. They can also be packed according to customer requirements by grade and weight in plastic bags with the bag openings sealed tightly, then placed in rigid cardboard boxes and stored in a cool, dry, dark place at a room temperature of about 15°C and a relative air humidity below 50%. Prevent rodents and insects, and frequently check the storage condition.

2. Fresh-keeping of shiitake mushrooms There are many fresh-keeping methods for shiitake mushrooms, including quick-freezing, refrigeration, chemical, controlled-atmosphere and microwave methods. (1) Dehydration and cold-storage fresh-keeping: Stop spraying water 10 hours before harvest, harvest at 70-80% maturity, carefully select and remove impurities, cut off the stem base, grade according to customer requirements, then place the shiitake mushrooms gill-side down on mats or bamboo blinds and air-dry them in sunlight. In autumn and spring, air-dry for about 3-4 hours; in summer, with strong sunlight, air-dry for 1-1.5 hours. After sun-drying, the dehydration rate of the shiitake mushrooms is 25%-30%, that is, 100 kg of fresh shiitake mushrooms becomes 70 kg-75 kg after drying. At this point, the stem feels moist when pinched by hand, and the gills have slightly shrunk. Pack by grade and fixed quantity into paper boxes, put a fresh-keeping bag over each box, then place them in cardboard boxes and store at 0°C. (2) Sealed-package cold-storage fresh-keeping: After fresh shiitake mushrooms are carefully selected and trimmed, place them gill-side up in plastic bags and store at about 0°C. Generally they can be kept fresh for about 15 days, suitable for self-service supermarkets@#@136@#@.