Introduction to Infrared Drying of Traditional Chinese Medicine Slices

Today, I will share some experimental data on infrared drying of traditional Chinese medicine slices, specifically using an intermittent infrared oven. To facilitate comparison, the size of the oven is the same as the hot air circulation oven used in earlier experiments.

Chen Pi is a widely used traditional Chinese medicine slice made from dried tangerine peel. It is primarily harvested from Xinhui district in Guangdong, known as “Guang Chen Pi.” It is dried or sun-cured and stored for over a year before being sold. Its primary properties include a bitter and pungent taste, and it is used to regulate qi, strengthen the spleen, dry dampness, and transform phlegm. It is often used in conjunction with hawthorn and Shenqu for treating food stagnation and qi obstruction.

Huang Bai is the dried bark of a tree, appearing in plate or shallow groove forms. It is yellow-brown, with a mild scent and bitter taste, and is associated with the kidney and bladder meridians. It is mainly used for treating damp-heat diarrhea, night sweats, nocturnal emissions, eczema, and sores.

Firstly, it is essential to understand the ambient infrared absorption spectra of the medicinal slices. Taking “Chen Pi” (dried tangerine peel) and “Huang Bai” (Phellodendron bark) as examples, these plant-based materials share a common characteristic: they are sensitive to high temperatures. High temperatures can alter their organic molecular structure and diminish their medicinal properties, potentially leading to surface carbonization. The infrared absorption peaks for Chen Pi and Huang Bai are found within the 3950-2850 and 1750-1200 bands. The required wavelength range for the infrared radiation source is determined through calculations, and carbon fiber heating tubes with different bandwidths are selected for the drying process. These tubes have powers of 500W, 1000W, and 1500W.

Due to the material characteristics of Chen Pi and Huang Bai, the drying temperature must not exceed 70 degrees Celsius. Care must be taken when setting the oven temperature as excessive heat can compromise the final product quality. The drying process for Chen Pi and Huang Bai can be divided into three stages: high-temperature heating, constant temperature drying, and cooling and airing.

In the first stage, after placing the products in a single layer on the shelf and closing the oven door, the oven temperature is set to 65 degrees Celsius. This temperature has been verified to minimize the loss of active ingredients. During this process, no humidity control is needed; attempting to do so would increase product shrinkage and worsen the appearance. After about one hour of drying, the products begin to soften and release a significant amount of internal moisture, leading to the second stage.

In the second stage, the temperature is gradually reduced to 45 degrees Celsius with a drying time of six hours. During this process, to ensure uniform shape, the material is flipped periodically, and adjustments to the stainless steel mesh tray are made. After six hours, the constant temperature drying is halted based on the actual drying results.

The final stage involves setting the oven temperature to 30 degrees Celsius and initiating humidity control. After airing for one hour and assessing the drying results, the products are removed. If the weather permits, products in this stage can be aired under direct sunlight outdoors, reducing electricity costs and shortening the drying time.

These stages are based on experimental data. In mass production, the drying time and insulation time must be adjusted according to the actual drying volume and industrial oven space.

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