One of the key issues during the herbs drying process is the high moisture content, which is usually above 70%. During the processes and stages of picking, transportation, storage, and sales, if not handled properly, the materials are prone to deterioration and spoilage. Especially in tropical and subtropical regions, it is estimated that the loss rate can reach as high as 35%-45%.

The advantages of Naisda's drying and dehumidification machine drying solution

(1) The fully automatic control system can select the optimal drying temperature and humidity according to the process requirements of different products, completely solving the problems such as long drying time, high temperature and high energy consumption that exist in other drying methods. It has unparalleled superiority.

(2) The use of high-efficiency centrifugal fans ensures strong air force, uniform air flow distribution, and low noise. This enables the material to dry evenly and quickly.

(3) During the drying process, the material does not deform, crack, change color, deteriorate, oxidize, or become spoiled. The drying is thorough, and the rehydration property after drying is good. The loss of nutritional components is minimal. The storage period is long, and it more effectively protects the color, aroma, taste, shape and active ingredients of the dried product.

(4) The overall design of the unit is integrated, and it can be put into use by simply connecting the pipelines and power supply on site. The operation is convenient. Once the parameters are set, automatic control can be achieved, and the reliability is high.

(5) It requires less investment and yields quick results. It can be transformed using old kilns, garages, etc., and can be relocated to save land area. It is simple and convenient.

Constant-speed drying stage

The Naisida high-temperature dryer takes about 5-6 hours to heat up. After being placed in the curing room, the temperature reaches 60℃ within two hours. The purpose is to make the fresh sausages reach a uniform internal and external temperature within 2 hours. The long-temperature process is also a seasoning and fermentation process for the meat, which can control the meat from changing color or flavor. After preheating, the temperature is adjusted to 45-50℃, and the humidity is within the range of 50-55%. During this stage, the surface moisture has evaporated, and the color changes from the initial grayish-white to a light red. This stage is the color-changing period. Then, the sausages are taken out of the curing room, their heads and tails are reversed and hung, and they are sent back into the curing room to enter the second stage of drying process for the sausages.

2. Decelerated drying stage

The process lasts for 15 to 18 hours, divided into two stages: the coloring stage and the contraction setting stage. During the coloring stage, the temperature is controlled at 52-54℃ for 4-6 hours, with the humidity maintained at 45%. The sausage gradually changes from light red to bright red, and the casing begins to contract. To prevent the surface of the casing from forming a hard shell, after the coloring stage, ventilation cooling methods should be adopted for processing. The drying dehumidifier stops heating, the exhaust port is opened to discharge the hot and humid air, and cold air is added for cold air drying. This can cause the surface temperature of the sausage to drop rapidly, facilitating the migration of moisture from the internal part of the anus to the surface. The contraction setting stage is divided into two parts: the contraction setting stage. It lasts for 11-12 hours. During this period, the amount of water in the sausage's interior continues to decrease, and the sausage significantly contracts. The surface appears uneven. The overall shape is basically determined. In the middle stage of the contraction setting, that is, 5-6 hours after the start of the contraction setting, a half-hour cold air cooling method is adopted to alleviate the contradiction between surface water evaporation and internal water migration. By the end of the contraction setting, it is completed.

3. Rapid drying stage

In this stage, the determining factor that restricts the drying speed is temperature. To enhance the drying speed, the temperature is raised to 55-60℃, and the drying time is controlled at 22-24 hours. The relative humidity is maintained at around 35%, and the final drying moisture content of the sausage is controlled below 17%.

The moisture content of ceramic bodies generally ranges from 5% to 25%. The moisture of the body consists of equilibrium moisture and free moisture. Under a certain air condition, the limit of drying is to make the body reach the equilibrium moisture. The equilibrium water is a part of the bound water. Its amount depends on the temperature and relative humidity of the drying medium. When the bound water is removed, the volume of the body does not shrink, which is relatively safe.

Under stable drying conditions, there is a certain relationship between the surface temperature, moisture content, drying rate and time of the raw material. Based on the changing characteristics of this relationship, the drying process can be divided into three stages: heating stage, constant-rate drying stage, and decelerated drying stage.

Heating stage

Since the heat transferred by the drying medium to the surface of the clay body per unit time is greater than the heat consumed by the evaporation of surface moisture, the temperature of the heated surface gradually increases until it equals the wet-bulb temperature of the drying medium. At this point, the heat gained by the surface and the heat consumed by evaporation reach a dynamic equilibrium, and the temperature remains constant. During this stage, the moisture content of the clay body decreases and the drying rate increases.

2. Constant-speed drying stage

During this stage, the non-bound water is still being discharged. Due to the high moisture content in the green body, the amount of water evaporated from the surface determines how much water can be replenished internally. That is to say, the speed of water movement within the body (internal diffusion speed) is equal to the water evaporation speed at the surface and also equal to the external diffusion speed. Therefore, the surface remains in a moist state. When the constant-rate drying stage ends, the moisture content of the material drops to the critical value. At this point, although the internal part of the material still contains non-bound water, bound water begins to appear in the surface layer.

3. Decelerated drying stage

During this stage, the moisture content of the raw material decreases. The internal diffusion rate cannot keep up with the evaporation rate of surface moisture and the external diffusion rate. The surface no longer remains moist, and the drying rate gradually decreases. Due to the reduced heat required for surface moisture evaporation, the material temperature begins to gradually increase. The vapor pressure of water on the material surface is lower than the saturated vapor pressure at the surface temperature. This stage is for removing bound water. The material does not undergo volume contraction and does not produce dry waste. When the water evaporation rate of the material decreases to be equal to the equilibrium moisture content, the drying rate becomes zero and the drying process stops.