What is the Pot Still distillation?

Malt Whisky is distilled twice - although a few distilleries may undertake a third distillation - in Pot Stills which resemble huge copper kettles. The spirit is driven off from the fermented liquid as a vapour and is then condensed back to a liquid.

In the first distillation the fermented liquid, or wash, is put into the Wash Still. which is heated either directly by fire or by steam-heated coils. At this stage the wash contains yeast, crude alcohol, some unfermentable matter and the by-products of fermentation. During the process of boiling the wash, changes take place in its constituents which are vital to the flavour and character of the whisky.

As the wash boils, vapours pass up the neck of the still and then pass through a water-cooled condenser or a worm, a coiled copper pipe of decreasing diameter enclosed in a water jacket through which cold water circulates. This condenses the vapours and the resulting distillate, known as low wines, is collected for re- distilling. The liquor remaining in the Wash Still is known as pot ale or burnt ale and is usually treated and converted into distillers' solubles for animal feed.

The low wines are distilled again in the Spirit Still, similar in appearance and construction to the Wash Still but smaller because the bulk of liquid to be dealt with is less. Three fractions are obtained from the distillation in the Spirit Still. The first is termed foreshots, the second constitutes the potable spirit, and the third is called feints. The foreshots and feints are returned to the process and redistilled in the Spirit Still with the succeeding charge of low wines. The residue in the still. called spent lees, is run to waste.

In the case of the Spirit Still, the design of the still, the height of the head (or top) of the still and the angle of the wide-diameter pipe or Lyne arm, connecting the head to the condensing unit, are all very important and have an effect on the distillate.

The Pot Still has changed little in general design over the centuries.

© SWA 1995