Materials that need to be prepared in advance include: 500g sweet potatoes, a scraper, a piece of gauze, and a grater.

1. Cut sweet potatoes into cubes.

2. Use tools to rub into silk.

3. Add water and rub thoroughly.

4. Filter with gauze.

5. Let the filtered water stand for a day.

6. Put it in a basin and dry it in the sun for 3 days.

7. Dry the water and take it back, and you are done.