What is Chach (Buttermilk)?

In India, the milk was boiled, cooled down to warm, fermented to make Dahi Yogurt. The Dahi Yogurt was churned in the cool morning hours. The Makhan (White butter) would float that was skimmed off. After the butter was removed, the remainder was called Chach. Chach was low in fat (Makhan was removed), with live culture, and most of the lactose was changed into the lactic acid.

Unfortunately, the British called it Buttermilk. This is totally a different product than the buttermilk sold in United States.

In the olden days, in United States, the raw milk was churned to skim off the butter. The remainder of liquid turn slightly sour was known as Buttermilk.
Now a days, the culture is added to pasteurized milk to make Buttermilk in United States. The end product is thicker, the culture is not alive, and it is full of lactose.