Why the Zhuang Minority like soured food?

Guilin is in Zhuang Minority Area. In 2001, I first came here, I found people here like to eat soured food. like soured fish, soured meet and soured duck. For me, it is another new taste, however I liked it immediately.
Have you ever think why Zhuang people like eating soured food? There are two reasons. One is the Zhuang people's main food is made of sticky rice. The sticky rice is hard to digest while soured food can accelerate digestion. The other is that soured food is easy to keep for a long time. Zhuang people used to live in the mountains and it usually cost them a whole day or even longer to go outside and be back.
Sticky Rice:

Soured Fish: