This situation is caused by adding flour during the production process, leaving it for too long, improper storage, etc.

1. Flour is added during the production process to make it white in color.

2. If left for too long, it will oxidize after contact with air, causing the color to turn white.

3. Improper storage will cause the sweet potato vermicelli to become damp and moldy, producing white mold. If the sweet potato vermicelli turns white, smell it first. If there is a peculiar smell, it may be moldy and do not eat it anymore.