Stress analysis and crack prediction of microwave vacuum drying of wheat

Wheat is prone to stress cracks during microwave vacuum drying, which affects its quality. Therefore, this study used a texture analyzer compression test, combined with the generalized Maxwell model, to establish a stress model for wheat, analyze its stress relaxation behavior and changes in load-bearing capacity after drying, and explore the interactions between moisture, temperature, and stress.

When the drying temperature is between 50 and 70 °C, wheat shows a significant increase in cracking, its load-bearing capacity decreases rapidly, and it is prone to breaking during storage. Although raising the temperature accelerates the internal moisture diffusion, it also damages the wheat structure, causing cracks to form. The ease of moisture migration is reflected by the activation energy, and its relationship with the effective moisture diffusion coefficient reflects the balance between energy and efficiency in moisture diffusion. Temperature and moisture content on a wet basis jointly affect the stress in wheat: when the moisture content is below 14%, stress first increases and then decreases with temperature; when above 14%, it first decreases and then increases. Stress exceeding the strength limit can trigger cracks and further reduce wheat strength.

To reduce cracking and lower breakage rates, the drying process is optimized as follows: wheat is heated from room temperature to 40 °C at a rate of 2.86 °C/min, held at this temperature for 7 min, and then heated to 61.4 °C at a rate of 1.63 °C/min until completion. This process can effectively control wheat breakage and cracking, providing both theoretical basis and practical reference for microwave vacuum drying. © 2026 Society of Chemical Industry.