The first stage is the warming and drying stage. The temperature in the drying chamber rises to 30 ° C - 35 ° C, the circulating wind speed is 2.3 m / sec, and the temperature is 30 ° C - 35 ° C. When the circulating wind speed is 1.3 m/s, the transfer of hot air and the diffusion and evaporation of fresh fruit free water are accelerated, especially when the fruit cortex loses water by 15%, the epidermis shows wrinkles, and the structural water in the pulp also slowly oozes out from the cortical pores. The sub-period speed dehydration, the concentration of sugar in the fruit is increased, the activity of the activated enzyme in the fruit is inhibited, and the main components such as polysaccharides, vitamins and amino acids are protected from being transformed or lost, especially for the red pigment, and the dried fruit color is Red quality is high. This stage lasts about 3 hours.

The second stage is the constant speed drying stage. Fresh fruit at 35-45 °C due to water infiltration in the fruit, the skin layer gathers sufficient non-bound water, because the surface water vapor pressure is basically the same as the temperature and pressure, and the internal moisture of the pressed fruit quickly moves to the surface to meet the vaporization of the epidermis. need. The draining fan starts up by itself and the drying time takes about 4 hours.

When the water loss rate in the third stage reaches nearly 50%, the indoor temperature naturally rises to 45 °C-55 °C, and the circulating wind speed can be lowered. The less water in the fruit, the shorter the dehydration time. This period lasts about 10-12 hours. A large amount of dehydration reduces the shape of the fruit, that is, it is usually in a semi-dry state. In this period, the water is weighed and the water in the fruit is about 30%.
The fourth stage is the slowdown drying stage. When the water content of the fruit drops to a certain value (about 30%), the thermal conductivity in the fruit becomes smaller, and the temperature difference between the inside and the outside increases. When the indoor hot air reaches 55 °C-60 °C, the water in the fruit is less and less, and the moisture is The evaporation rate of the external migration decreases, and the water seepage is slow, so it takes a considerable time to slowly discharge. This period will take about 12-15 hours to reduce the water content of the fruit to less than 13%.

The common phenomenon of drying of fresh fruit is that the surface water diffusion is greater than the internal diffusion rate, and the free water extravasation rate in the fruit is greater than the structural water extravasation rate. This is because the high sugar content in the fresh fruit is difficult to dehydrate and dry. If the temperature in the drying chamber is too high, the surface water dispersion of the fresh fruit is too fast, and the extravasation of the water inside the fruit is not supplied, the epidermis will foam, blocking the drainage pores, and the water inside the fruit will not be discharged. Decolorization and quality degradation. The fresh fruit is firstly subjected to surface oil cold immersion treatment, and the appropriate temperature and wind speed, the temperature of the skin through the pores is increased while the skin is dehydrated, which is beneficial to the moisture discharge inside the fruit, thereby accelerating the drying speed, and Can guarantee the quality of drying.