The reason why Kuay Teow turns yellow after being cooked can be explained from two aspects: the ingredient list and the production steps.

1. In terms of ingredient list: the rice or rice noodles used as raw materials for Kuay Teow may have been slightly contaminated by microorganisms during the production process. This may cause the color of the kway teow to change after cooking.

2. In terms of production steps: If the rice noodles are not fully cleaned and disinfected during the production process, or are contaminated during the processing, the color may change after cooking.