2. When ceramic tiles are used in into the pit, the soil covered should be slightly wet, not sandy soil (heat conduction is too fast).

3. Cover with soil and build a bonfire. When the stick turns red, cover it with green branches (or take local materials) and leave it for 25-30 minutes.

This test is to control the fire. The function of sweet potato is as follows: 1. Sweet potato is rich in protein, starch, pectin, cellulose, amino acids, vitamins and various minerals, and it is one of the longevity food, with sugar content of15%-20%. Sweet potato not only has comprehensive nutrition, but also has little-known effects of preventing sub-health, such as losing weight, bodybuilding and anticancer. 2, sweet potato contains a lot of starch, which makes people feel full after eating, thus reducing food intake. Therefore, patients who lose weight can appropriately replace the staple food with sweet potatoes, which can achieve the effect of losing weight and slimming; 3. Sweet potato contains a lot of dietary fiber, carotene, vitamins, such as vitamin A, vitamin B, vitamin C, and trace elements such as potassium, iron and copper. Its nutritional value is relatively high, and it is called balanced food by nutritionists. 4. After the sweet potato is cooked, some starch will change. Compared with raw food, it can increase dietary fiber by about 40%, which is beneficial to intestinal peristalsis, so some constipation patients can suggest eating more.