Steam distillation is a technique employed to distill alcohol or extract essential oils from organics by passing steam generated in a pot still through the plant material. Temperature sensitive compounds which would normally decompose through simple distillation vaporise at lower temperatures when subjected to steam in the vapour chamber or column of the still. This allows for the separation of essential oils, which tend to be less soluble in boiling water, from chemically complex materials. When the steam passes through the organic material tiny pockets that hold the essential oils open to release the essential oil molecules without damaging or burning these delicate components. The distillate will contain a mix of water vapour and essential oils which return to their liquid form in the condensing recipient and are separated using a Florentine separator (item 66500).
Both the essential oils and the water called floral water or hydrolats is retained. The distillation procedure is the same as for the simple distillation method with the exception that distillation takes place by means of steam.
As for essential oils, using steam for alcohol distillation permits the distillate to retain the more delicate flavours and aromas which would otherwise breakdown if subjected to high temperatures. This process is typically used to extract essential oils from aromatic plants to flavour liqueurs. Alternatively alcohol may be distilled from fermented matter placed in the column of an alembic such as pressed grape skins left over from wine making.
There are obvious advantages to steam distillation with commercial applications in the food, medical and chemical industry, for example aromatic oils, hydrolats, perfumes, essences and flavoured liqueurs.