Why does Balsack bulge?

Fully fermented. Basak is a Kazak snack, just like the Han fried dough sticks, Basak and milk tea are often a pair of conjoined. Just like steamed bread and porridge in China. It is mainly made of flour and milk. When the flour is fully fermented, it will swell. Kazakh herders are hospitable, and this kind of fried pasta, Balsack and milk tea is generally used to entertain guests.