curdle

Short definition from Wiktionary

Verb

1. 1
   To form curds so that it no longer flows smoothly; to cause to form such curds. (usually said of milk)
2. 2
   To clot or coagulate; to cause to congeal, such as through cold. (metaphorically of blood)
3. 3
   To cause a liquid to spoil and form clumps so that it no longer flows smoothly.