Key Points and Methods for Dehydrating and Drying Shiitake Mushrooms Explained

First, if the quantity of shiitake mushrooms harvested or purchased is very large and there is not enough time to dry them the same day, they must be spread out in a cool, ventilated place and piled as thinly as possible to prevent internal heating that would affect the quality of the dried product.

Second, in the early stage of drying, the temperature inside the drying oven or drying room should rise slowly and gradually, generally not exceeding 5°C per hour. If the temperature rises too quickly, the surface of the mushroom body shrinks rapidly, causing the capillaries to become blocked, which instead makes it difficult for moisture inside the mushroom body to escape. In mild cases, this causes the mushroom body to shrink and wrinkle, forming a wavy surface; in severe cases, a hard shell forms on the surface of the mushroom body, causing the gills to turn black and making drying difficult, and the quality of the shiitake mushrooms declines severely. In the early stage of drying, the temperature should be kept between 30 and 35°C.

Third, after 6 to 8 hours of drying (the middle stage), most of the moisture in the fresh mushrooms has already been lost. At this point, the positions of the drying trays should be adjusted: those at the air inlet should be swapped with those at the air outlet, and those on the upper layer should be swapped with those on the lower layer. For shiitake mushrooms in the same drying tray, if there is a large difference in their degree of drying, they should also be picked out and adjusted appropriately so that the degree of drying is basically similar.

Fourth, after 8 to 9 hours of drying (the middle-to-late stage), the moisture in the mushroom stems has basically disappeared and they have softened. When they can be twisted by hand without breaking, it is best to bend the mushroom stems and tuck them inside the mushroom caps to increase the commercial value of the dried shiitake mushrooms.

Fifth, after the initial drying stage, the middle drying stage, and the middle-to-late drying stage, shiitake mushrooms then enter the late drying stage, which takes about 10 hours in total. At this point, except for the mushroom stems, the fruiting bodies have generally all dried. The drying temperature can be raised to 60°C to use more heat energy to further evaporate the colloidal water in the mushroom bodies, but it should not exceed 60°C, because shiitake mushrooms are rich in protein. When the temperature is too high, it will destroy the nutritional components of the shiitake mushrooms, and at the same time affect the formation of the aromatic substances in the shiitake mushrooms, and may even produce combustible gas, causing the product itself to burn.

Sixth, when the moisture content of the shiitake mushrooms drops to about 13% (the fixing stage), heating can be stopped. Close the air inlet and air outlet so that the dried shiitake mushrooms are left to steep in the drying oven, allowing the temperature to drop naturally. When the temperature approaches room temperature, the oven can be opened to take out the mushrooms for grading and packaging.