Water and steam distillation

The still is divided into two levels by a grid or rack. Water is poured into the bottom up to a level below the grid, and the raw material is packed on top.

When heated, the water boils and steam rises through the mass of material. The steam here is saturated — carrying more moisture than steam from a separate boiler, because it has only just left the water surface.

The rest is the same as every distillation: through the condenser, cooling, separation in the receiver.

An important practical detail is watching the water level. If the water runs so low that the material touches the hot bottom, the batch will smell burnt — and at that point the method has quietly turned into something worse than water distillation.

It sits between the other two methods in the degree of change. The material is not soaked, so there is less hydrolysis than in water distillation, but saturated steam and long run times still cause more change than direct steam.

For most leaf and stem materials — lemongrass, cajuput, mint, holy basil — the difference from direct steam is small. With ester-rich materials the difference starts to show.

Steam pressure and dryness cannot be adjusted independently, because the steam is generated inside the still.

The water at the bottom is limited, so long runs need topping up, and each top-up makes the temperature fluctuate.

With heavy, easily compacted materials, the mass can still block the steam path, just as in direct steam distillation.

It is very hard to tell apart from direct steam distillation on an analysis alone, because the two methods give similar results. The only reliable way is to ask the supplier about the equipment.

That is also why this page exists: if you do not know how the three distillation methods differ, you will not think to ask.

This is a common medium-scale configuration in Vietnam — larger than the household copper still but without investment in a separate boiler. Many lemongrass and cajuput distilleries in the central region and the Central Highlands use it.

It is also the natural first upgrade when a household distiller wants better quality but cannot yet afford a separate steam system: just add a grid and raise the material above the water.