Vegetable matter such as lucerne is dried; the latter is heated and then pressed. The liquid is treated in an evaporator employing, as heating fluid, low-pressure steam supplied by an ejector-compressor fed with high-pressure steam supplied, for example, by a nuclear power plant. Low-pressure steam taken from the outlet of the compressor-ejector is also employed to heat the lucerne at. The effluent leaving the evaporator is introduced with the remainder of the high-pressure steam into a drying unit in which air from the environment is preheated. The hot air is employed for drying the moist pressed matter.