Why does Black Gram Batter turn fluffy only when stone ground?

Idly and Vada two major recipes of South India. For those dishes Black Gram Batter is the key ingredient. This soaked balck gram when ground in a mixer or food processor makes idly and vada hard and the batter is not fluffy. While if the black gram batter is ground in wet grinder it becomes fluffy and the idly, vada made out of it is more soft and tasty. Why?

Best Answer

A blender will cut or shatter what you put into it while leaving the structure of the pieces relatively intact. A grinder or mortar will apply pressure, causing cell walls to rupture, so molecules in the food that were previously kept separate can react, and fermentation relevant microbes (which, if I remember correctly, are important for idly?) have good access to all of the lentil and not just ruptured cells at the edges...