It is a traditional custom to eat tofu after coming out of the cell, which means clean and white.

There are also several sayings that in the past, prison food was poor, prisoners were malnourished, and they needed to be supplemented with nutrition after they were released from prison. Tofu is a high-protein food, and its price is relatively cheap. Therefore, eating tofu can quickly supplement nutrition and prevent indigestion caused by overeating other foods. Once soybean is made into tofu, it's hard to turn it back into soybean, which means you won't go back and start over. Tofu is pure white, so eating tofu means being a good person in the future.