To evaporate is for a liquid to turn into vapour — molecules escaping from the surface into the air as heat or airflow drives them off. Molecules at the liquid’s surface gain enough energy to escape into the air; heat accelerates the process, airflow carries the vapour away, and low humidity keeps the gradient steep. Cooks evaporate deliberately — reducing a stock to concentrate its flavour, simmering milk down toward condensed milk — and food manufacturers do it at industrial scale, evaporating milk, juice, and sugar liquors in vacuum evaporators that boil at low temperatures to protect flavour. The reverse journey, condensation, returns vapour to liquid. Evaporation is one of the oldest concentration technologies: removing water to intensify flavour, reduce weight, and preserve — the physics behind everything from a demi-glace to a milk powder.