Question

what is tannin used for

Answer 1

biochemical used for deficeancy of proties in body

Answer 2

Tannin solutions are acid and have an astringent taste. Tannin is responsible for the astringency, colour, and some of the flavour in tea. 
 tannins are used in photography, as mordants in dyeing, clarifying wine and beer by precipitating proteins out of them, and as astringents in medicine.
Different colors, textures, and durability of leathers were achieved by using different formulations of plant tannins referred to as “tanning liqueurs”.