Why is it notrecommended to dry Chinese medicinal herbs at low temperature?

Why is it notrecommended to dry Chinese medicinal herbs at low temperature?

A customer said to me, "For thousands of years, the traditional drying method for Chinese medicinal herbs has been natural air drying, which can maximize the medicinal efficacy as well as maintain the shape and color of the herbs. Therefore, it is better to dry the herbs at low temperature."

I responded, "It is not recommended to dry Chinese medicinal herbs at low temperature!"

Natural air drying refers to the environment with a temperature not exceeding 20°C and a relative humidity not exceeding 60%.

The weather conditions are constantly changing, and it is not possible to have the suitable temperature and humidity for air drying Chinese medicinal herbs throughout the year, which makes it impossible to achieve large-scale drying using the natural air drying method.

In fact, ancient people have been using fire to dry Chinese medicinal herbs. The earliest written records of Chinese medicinal herb processing can be traced back to the Warring States period. By the time of the Han Dynasty, there were numerous processing methods documented, including steaming, frying, roasting, calcining, parching, refining, boiling, scorching, and burning. It is evident that heating to accelerate water evaporation and enhance medicinal properties has been of significant importance since ancient times.

The evaporation of moisture is directly related to temperature. The higher the temperature, the faster the molecular movement and evaporation. With the advancement of technology, people have discovered various heating methods such as electricity, natural gas, biomass pellets, air energy, and steam to increase temperature.

The drying temperature of the Chinese medicinal herbs generally ranges from 60°C to 80°C.

Controlling the drying temperature is one of the key factors to ensure the quality of the herbs. If the drying temperature is too high, it can lead to excessive dryness, affecting the quality of the herbs, and may even cause discoloration, waxing, volatilization, and component degradation, thereby reducing the medicinal efficacy. If the drying temperature is too low, the herbs cannot be fully dried, making it prone to mold and bacterial growth, leading to a decrease in quality and potential spoilage of the herbs.

 

Effective control of the drying temperature relies on professional Chinese medicinal herb drying equipment.

Typically, electronic temperature control is used to adjust temperature, automatically regulate humidity and air velocity, and set drying parameters in different stages to ensure the quality of the herbs.