A fat separator is the kitchen utensil used for draining away fat that has risen to the top of sauces, stocks, and gravies — the jug with the spout at the bottom. Hot cooking liquid is poured in and left to settle; the fat floats to the top while the lean juices sink, and pouring from the low spout delivers the defatted liquid while the fat stays behind. It mechanises the classic techniques — skimming with a spoon, chilling to lift the set fat — into a single vessel, and it works because fat and water separate by density every time. The result is cleaner stocks, lighter gravies, and sauces with the flavour but not the grease. A simple application of physics to the eternal kitchen problem: the fat always rises, and the separator is waiting underneath.