Lou fo tong (Chinese: 老火湯) is a distinctive variety of soup in Cantonese cuisine popular among Chinese people in Guangdong, Hong Kong, Macau, and overseas. These soups are usually made by simmering various vegetables, fruits, meat or Chinese herbs in a pressure cooker, vacuum cooker, claypot, wok or clay jar for a few hours, and are believed to have skincare, heart-protective, vision-enhancing, bile-reducing, and bone-strengthening benefits. Owing to the hot and humid climate in the Lingnan region, the locals have developed a penchant for drinking lou fo tong for its nourishing and health-boosting effects.[1][2]
According to experiments conducted by a research team led by Prof. Jiang Zhuoqin from School of Medicine and School of Public Health, Sun Yat-sen University, the calcium salts in animal bones are barely soluble in water. In the first experiment, the average calcium concentration in soup stewed with distilled water was only 1.0–1.2 mg/100 ml. In the second experiment, using an expensive vinegar-soaked ceramic pot, the calcium concentration reached 178 mg/100 ml.[3]
