What is the dephlegmator?

The term dephlegmator is derived from phlegm, the condensate of a heavy boiling liquid that precipitates and returns to the system. This means that a separating effect of the alcohol-water mixture does not take place by evaporation of the lower boiling liquid – as realized on the amplifier bottoms – but that the condensation of the heavier boiling liquids leads to an enrichment of the lower boiling components. The reinforcing effect of the dephlegmator (or reflux condenser) depends on
– from its heat exchange surface
– the cooling water flow
– the temperature difference between cooling water and alcohol-rich steam.

The size of the heat exchange surface depends on the design of the dephlegmator. There are two basic types:

In the water box dephlegmator, only a cylindrical, closed metal vessel with a cooling water inlet and outlet is embedded in the upper part of the amplifier. Since the heat exchange surface is relatively small, the reinforcing effect is also relatively weak.

Greater enrichment is possible with the tube dephlegmator, in which numerous tubes pass through a cylindrical vessel through which cooling water flows. If the dephlegmator is too warm, especially at the beginning of the distillation, this weakens its reinforcing effect. Flow and overflow can no longer be separated cleanly from the middle run. Therefore, when carrying out several successive distillations, make sure that the dephlegmator is cooled down before the next distillation.