1.Preparatory drying period for mushrooms
The fresh mushrooms shall be put into a heat pump dryer for preparatory drying at a temperature of 35°C, which should be continued for 1-4 hours to reduce its water content by 15-20%.
2.Constant-speed drying period of mushrooms
During this drying period, the moisture diffusion rate and the surface evaporation rate of fresh mushroom are basically the same. Generally speaking, after drying for 4-5 hours, the temperature should be gradually rose to about 50°C, equally to rising 2°C per hour. The air inlet and air exhaust holes should be closed by 1/3. In this stage, the mushroom shall generally be dried for 3 -4 hours. At this stage, the temperature should be controlled between 40℃-50℃. During this period, the fresh mushrooms are softened. Gradually, after the water has been evaporated, the edge of the mushroom begins to harder, the mushroom cover is shaped, and the thick part of the center become harder as well. As the water still exists in the core of the mushroom during this period, and the highest temperature is only reach to 50 ℃, the mushroom will not show a light yellow color.
3.Late drying stage of mushrooms
In this period, the water in the mushroom begins to decrease, the free water is basically exhausted, and part of the bound water is gradually drained out. In this period, the water movement speed in the fresh mushrooms obviously cannot keep up with the surface evaporation speed of the mushroom, thus the ventilation quantity do not need to be too large in order to save energy. Meanwhile, the drying temperature should be maintained at 50℃-55℃, and then the inside temperature and outside temperature of the mushroom tends to be the same. The air inlet and air exhaust holes should be closed by 1/2, and the temperature recovery hole should be opened by 1/2. The drying time shall be maintained for 2-3 hours. During this period, the mushroom becomes light yellow and began to produce fragrance.
4.The complete drying period of mushrooms
The main purpose of this period is to remove the residual water and the bound water in the core of the mushroom. The temperature is 58℃-60℃, and the drying time is 1-2 hours. All the inlet and outlet holes are closed, and the temperature recovery holes are all opened to allow the hot air to circulate internally. No fresh air is introduced. The circulating air volume can be reduced to medium or small, which is easy to produce aroma resulted by the interaction of acid and enzymes in the mushroom .
At the end of this period, the moisture content of the dried mushrooms is 11-13%, which meets the storage standard or export standard. You can use the following way to check the dry condition of the mushrooms: Pressing the junction of the cap and the stalk of mushroom with your fingers; lightly pinching the mushroom stalk. The mushroom can be easily broken with a clear and melodious sound. It could see that the mushroom gills are upright and intact, and the mushrooms maintain the original shape, the cap is round and flat, the surface is smooth in golden, and it emits the unique fragrance of the mushrooms. Shuntec heat pump drying equipment units are operated in phased manner, it allows you experience the fully automatic and temperature-controlled technology for drying, and customers can complete the drying process without manual duty. As the complete dried mushrooms have good color and full of aroma, the mushroom price is much higher than those dried mushrooms which are made by traditional coal burning, thus the customers who use Shuntec drying machine units are very satisfied.