The effect of ultrafine and coarse grinding on the suspending and precipitating properties of black tea powder particles

Traditional manufacture of instant tea by extracting and drying results in limited raw material utilization ratio and complicated processing procedures. Here, ultrafine black tea powders (10-50 mu m) and coarse black tea powders (100-500 mu m) were prepared to investigate their properties after brewing for up to 30 min in boiling water. The size of a stably suspending particle was 12-15 mu m, which was not affected by the grinding method and particle microstructure. Hence, the particle size criterion to produce soluble ground instant tea is proposed to be < 12 mu m. Particles larger than 30 mu m, comprised of carbohydrates, lignin, and protein, precipitated. The raw material utilization ratio of ultrafine powder (50.12%) was higher than that of coarse powder (35.70%), resulting in a higher amount of soluble carbohydrates and suspended particles. Moreover, ultrafine grinding reduced the precipitation ratio by delivering more insoluble health-benefiting components to the suspending liquid. (C) 2017 Elsevier Ltd. All rights reserved.