A system for monitoring phase separation is disclosed. The system includes a temperature control housing having an inlet and an outlet connection for a circulator; a bottle holder positioned inside the housing, the bottle holder having a body with a plurality of recesses for receiving test bottles, each recess having a back surface, a front opening, and a first light scanning component mounted on the back surface of the recess; a sleeve having a plurality of second light scanning components mounted thereon, the sleeve being disposed between the housing and the bottle holder, and each second light scanning component being aligned with one of the first light scanning components; and a lid latched onto the housing to hold the test bottles in place during testing.