The worm in a distillery is a coiled copper tube of decreasing diameter attached by the Lyne Arm to the head of the Pot Still and kept continuously cold by running water. The alcoholic vapours from the still condense as they pass through the worm. Both distillation and non-distillation uses of 'worm' in an inanimate sense refer to objects that spiral or coil. In the relevant distilling context, it is first attested in 1641, 'Put it into a Copper Still with a worme', though a captioned illustration of a worm and worm-tub appears in Lonicer's Naturalis Historiae OpusNovum, published in Frankfurt in 1551.
The worm was first developed in the sixteenth century. Condensing of spirit had previously been achieved simply by air cooling, consequently production of liquor was limited. Writing of sixteenth-century advances in distillation techniques. The most important innovation involved passing the delivery tube through a tub of water. At first the tube was carried straight across the tub, later diagonally. From about 1540- 50 the tube was coiled into a 'worm' which increased the cooling surface available.
In illicit as well as legal distilling operations the worm has always played a crucial role, being a comparatively difficult and therefore expensive piece of equipment for the coppersmith to fabricate, a cask often serving as a makeshift worm-tub, as shown on the picture.
Building you own condensor: