The term 'milk curdler' refers to a device or substance used to separate the solid and liquid components of milk. The two crossword solutions for this term are Rennin (6 letters) and Rennet (6 letters). Rennin is an enzyme found in the stomachs of young mammals, including calves, that helps them digest their mother's milk. Rennet is a mixture of enzymes derived from rennin that is used to coagulate milk, separating it into curds and whey.