Complete Guide to Drying Methods and Pest and Disease Control for Edible Mushrooms

Edible mushrooms have a high water content, tender fruiting bodies, strong after-ripening, and are prone to rot. During batch production or large-scale cultivation, the quality of the drying and processing directly affects the economic returns of the producer.

There are two categories of drying methods for edible mushrooms: natural drying and artificial drying. In the drying process, the speed of drying has a decisive influence on the quality of the dried product. The faster the drying speed, the better the product quality.

Natural drying uses sunlight as the heat source for drying and is suitable for varieties such as bamboo fungus, silver ear fungus, enoki mushroom, lion's mane, and shiitake. It is one of the oldest drying and processing methods for edible mushrooms in China. During processing, the fruiting bodies are spread flat on bamboo drying screens tilted toward the south, without overlapping each other. In winter, the tilt angle of the drying screens needs to be increased to boost sunlight exposure. When fresh mushrooms are spread out to dry, they should be turned gently to prevent damage, and generally it takes 2 to 3 days to dry them. This method is suitable for production and processing at small-scale farms. To save costs, some mushroom growers dry the mushrooms until half-dry and then carry out artificial baking. This must be properly managed according to weather conditions, light intensity, and the moisture content of the edible mushrooms; otherwise, the mushroom bodies may become twisted, deformed, and discolored.

Artificial drying uses drying ovens, drying baskets, drying rooms, or heat sources such as charcoal hot air, electric heat, and infrared radiation to bake the mushrooms so that the fruiting bodies are dehydrated and dried. This method dries quickly and gives good quality and is suitable for large-scale product processing. At present, artificial drying equipment can be divided by heat action mode into: (1) hot air convection drying, (2) thermal radiation drying, (3) electromagnetic induction drying. In China, equipment now widely used includes straight-line temperature-rising drying rooms, tempering temperature-rising drying rooms, hot air dehydration dryers, steam dehydration dryers, and infrared dehydration dryers.

The dehydration and drying processes for edible mushrooms are varied. Taking shiitake as an example, in order to make the mushroom shape round and neat, the cap edge thick and curled, the gills bright yellow, the aroma rich, and the moisture content reach the 12% export standard, the following steps must be well controlled:

1. Strictly control harvesting. Harvest when the mushrooms are at the eight-tenths mature stage and the caps have not yet opened. At this time, the shiitake spores have not been released, and after drying the aroma is strong and the quality is good. Do not spray water at the time of harvest. The freshly harvested mushrooms should be placed in bamboo baskets and must not be transported in cloth bags or nylon bags, so as to prevent compression, damage, and deterioration.

2. Spread them out to air promptly. The freshly harvested mushrooms should promptly be spread on bamboo screens in a ventilated, dry place to speed up evaporation of moisture from the surface of the fruiting bodies. Never place fresh mushrooms on damp ground, as this can cause browning and affect the color of the dried mushrooms. After airing, the fresh mushrooms are generally handled in three ways according to market requirements: stems not trimmed, stems half trimmed, and stems fully trimmed, while debris such as wood chips and broken mushrooms are picked out.

3. Sort and load for baking. It is required to harvest on the same day and bake on the same day. Sort the fresh mushrooms by size, thickness, and shape into grades, and arrange them evenly on the upper drying screens with the stems facing up, while placing lower-quality ones on the lower layers. To prevent intensified metabolism of shiitake cells during baking, which can cause the caps to stretch open, the color to turn white, and quality to decline, the empty machine can be heated to 38°C to 40°C before the fresh mushrooms are put in, and then the mushrooms are mixed and loaded onto the racks.

4. Control the heat and dry at low temperature. Shiitake has a moisture content as high as 90%, so it must never be dried rapidly at high temperature. Operation after starting the machine must be standardized: while igniting and raising the temperature, start the exhaust fan so that the heat source is evenly introduced into the drying room. When the temperature rises to 35°C to 38°C, place the drying screens with the arranged fresh mushrooms into the drying room layer by layer, prompting the fruiting bodies to shrink, increasing the degree of curled edges and the thickness of the mushroom flesh, and improving the quality of the dried mushrooms. Drying room temperature control: maintain 38°C to 40°C for 1 to 4 hours, 40°C to 45°C for 4 to 8 hours, 45°C to 50°C for 8 to 12 hours, 50°C to 53°C for 12 to 16 hours, 55°C at 17 hours, and 60°C from 18 hours until drying is complete.

5. Pay attention to moisture removal and ventilation. As moisture inside the fruiting bodies evaporates, poor ventilation in the drying room can cause the color to become grayish brown and reduce quality. Operational requirements: fully open the moisture exhaust windows from 1 to 8 hours, maintain ventilation at about 50% from 8 to 12 hours, maintain ventilation at 30% from 10 to 15 hours, and after 16 hours, when the fruiting bodies are basically dry, the moisture exhaust windows can be kept closed for a long time. When pressing the cap with a fingernail feels hard and leaves only a slight nail mark, and turning them over produces a rustling sound, this indicates that the shiitake is dry enough and can be taken out of the room to cool and be packaged.