to
turn bad, to fail or to go
wrong; to spoil or make sour. From the regular
definition of curdle meaning to
change milk into curd or to
turn any liquid into a soft,
solid substance like this; to coagulate,
clot or congeal. Curd is the thick, soft, almost
solid substance that separates from
milk when it becomes sour and which is eaten as food or used when making cheese.