What should be paid attention to during the processing of shiitake mushrooms?

Shiitake mushrooms have long been known as a mountain delicacy, rich in nutrients and delicious in taste. Their dried products (commonly known as dried mushrooms) are classified into flower shiitake, winter shiitake, thick shiitake and thin shiitake. However, because current drying techniques and other methods lag behind, dried shiitake products suffer from problems such as poor color, weak aroma and unattractive mushroom shape, seriously affecting their commercial value. If shiitake mushrooms are processed well, their value can be increased by nearly 1 times. The following discusses the key techniques of processing methods for dried shiitake products:

1. Sun-drying method

Stop spraying water on the mushroom bodies 2 days before harvesting shiitake mushrooms, and choose clear weather. Harvest when flower shiitake and thick shiitake are 5-7 mature (the partial veil is partially broken), or when winter shiitake and thin shiitake are 7-8 mature (the partial veil has broken, the cap edge has not fully expanded and is slightly curled inward, the gills have fully extended and turned from white to yellowish brown or dark brown). Hold the base of the mushroom stem with your hand and gently twist to lift the mushroom body. Grade the harvested fresh mushrooms by size and thickness, and spread them on drying screens with the stems facing down (a shade net can be laid on the screen to absorb more heat). Tilt the drying screen at a 30° angle to the ground, with the inclined surface facing the sun to receive direct sunlight, and adjust the orientation of the drying screen as the sun moves. Fresh mushrooms can be sun-dried in 3-5 sunny days. The shorter the sun-drying time, the better the quality of the dried mushrooms. At this point, the moisture content of the shiitake mushrooms is about 20%, still higher than the standard moisture content of below 13% for dried mushrooms, and the aroma of shiitake mushrooms is only produced after baking at a temperature above 50°C. Therefore, first sun-drying the fresh mushrooms until semi-dry and then forced dehydration with hot air is a relatively economical and effective method in dried shiitake production.

2. Oven-drying method

The performance of the drying equipment must meet the requirements of the shiitake mushroom drying and dehydration process, and the temperature and flow rate of the drying air must be adjustable according to process needs. At present, drying cabinets are mainly used as drying equipment for shiitake mushrooms. The harvested fresh mushrooms should be sorted promptly and moved into the drying cabinet within 3-4 hours. Classify them onto screens according to mushroom body size and thickness and whether the cap is open or closed, arrange the gills uniformly facing upward or downward in neat rows, place large, moist and thick shiitake mushrooms in the middle of the screen, place small mushrooms and thin mushrooms on the upper layer, and place poor-quality mushrooms and mushroom stems on the bottom layer.

The entire drying process is divided into 4 stages:

(1) Preliminary drying stage. This is the rough dehydration stage just after the shiitake mushrooms enter the cabinet. The temperature should be controlled at 30-50°C, and the moisture should be reduced to 75%. For shiitake mushrooms harvested on sunny days, the starting temperature can be 40°C, and the rough dehydration time can be 3-4 hours; for shiitake mushrooms harvested on rainy days, the starting temperature should be 30°C, and the rough dehydration time should be 4-5 hours. During this period, because the shiitake mushrooms have high humidity and the cells have not yet been killed, the temperature must not remain below 35°C for a long time, and the air inlet and exhaust outlet should be opened wide so that moisture can be discharged as quickly as possible, the temperature rises evenly, increasing by 1-2°C per hour.

(2) Drying stage. The fruiting body continues to evaporate moisture and gradually enters a hardened state, the shape tends to become fixed, and the degree of drying reaches about 80%. The temperature slowly and evenly rises from 50°C to 55°C, requiring 8-10 hours. At this stage, the air inlet and air outlet should be reduced.

(3) Post-drying stage, also called the shaping stage. The moisture evaporation rate of shiitake mushrooms slows down, the mushroom body begins to harden, and this plays a decisive role in the shape of the dried mushrooms. The temperature is maintained at 55°C, requiring 3-4 hours.

(4) Completion stage. The temperature in the drying cabinet rises from 55°C to 60°C, and maintaining it for about 1 hour can kill insect eggs, until the internal moisture of the shiitake mushrooms is consistent with the surface moisture, the moisture content is 11-13%, the color is glossy, and drying is complete.

3. Precautions:

(1) Fresh mushrooms must not be stacked, so as not to affect the drying speed of shiitake mushrooms and the uniformity of dehydration among the mushroom bodies.

(2) The drying operation should be carried out on sunny days. On sunny days, the relative air humidity is low, which helps reduce drying time.

(3) The drying program should be set according to the different conditions of the fresh mushrooms. For example, the gills of thin mushrooms and rain-soaked mushrooms often lie flat, so such mushrooms can first be pre-dried in the sun (until the cap is glossy and the gills stand up), and then transferred to conventional drying treatment.

(4) Strictly control the drying temperature at each stage. If the temperature is low, the gills of the dried mushrooms turn whitish; if the temperature is too high, the gills become too yellow or scorched yellow. During drying, the temperature must not fluctuate abruptly, otherwise the surface of the dried mushrooms will have no gloss.

(5) Bag the dried mushrooms after they have properly reabsorbed moisture. Bagging immediately after drying will break the dried mushrooms and affect their appearance. The dried mushrooms should be graded and bagged after proper moisture reabsorption, and during storage and stacking, care should also be taken to prevent the dried mushrooms from being crushed and broken by pressure.