The stone circular mill and horse gin

The trough — the chase in some accounts — is a circular channel, typically cut from a hard local stone in several curved segments and bedded on a level base. Its width takes the runner with a little clearance either side, and its floor is worn concave by generations of use. The runner itself is a thick disc of stone with a square hole through the centre, and the axle passes through it into a fixed upright post at the mill’s centre. Because the runner is rigidly mounted but travels a circular path, it does not roll cleanly: the inner edge is always trying to travel slower than the outer edge, so the stone scuffs and grinds as well as presses.

That scuffing is not a defect. It is what makes the mill work on apples, which are far too elastic to be reduced by a rolling load alone. A wheel that rolled perfectly would push apples along in front of it; a wheel that also drags tears the flesh apart and breaks the pips.

A person, usually a boy, stood by with a wooden paddle or a long-handled rake to push fruit back under the runner as it squirted out sideways, and to turn the charge over. The horse walked outside the trough on a beaten circular track, harnessed to the end of the axle by a wooden sweep arm — the gin in the older sense of an engine or contrivance, nothing to do with the spirit. Larger mills were driven by water, and a few late ones by belt from an oil engine.

An hour under a stone is an hour of maceration, and maceration is the variable that changes cider more than almost anything else at the front of the process. While the pulp sits, enzymes and mechanical damage release phenolic compounds from the skins and the flesh into the liquid phase, and pectin-degrading activity begins. Juice pressed from long-macerated pomace carries more tannin, more colour and more body than juice from fruit milled and pressed within minutes.

It also carries far more oxidation. The pulp is open to air for the whole crush, and polyphenol oxidase in the apple converts the phenolic substrates it meets into quinones, which brown and polymerise. This is why pomace under a stone mill goes from cream to russet to near-black, and why traditional West Country cider is a deep colour and comparatively soft in its tannin: much of the harsh, bitter fraction has already been oxidised and, later, dropped out with the lees.

Modern makers reproducing this effect deliberately talk about pomace conditioning or maceration and control it by the clock. The stone mill did it by default, because there was no other speed available.

A stone mill is enormously laborious for the volume it produces. It needs a horse, a person to lead or watch the horse, a person at the trough, and a building or a yard with a circular track in it. Throughput is a few hundredweight an hour at best. What it does not need is any machinery that can break, any money after the initial cutting of the stone, or any power beyond an animal that the farm already owned.

The scratter ended it. A toothed roller mill driven by a handle, a horse gear or later a belt could reduce the same fruit in a fraction of the time, in a machine two people could carry. Museum collections in Hereford and Somerset record the changeover through the nineteenth century, and the stone mills that survive in farmyards are mostly ones that were already ornamental by 1900.

A handful of producers have brought stone mills back into use for particular batches, on the grounds that the character is not reproducible by simply leaving hammer-milled pulp to stand. Whether that is true is genuinely contested: the crushing action and the oxidation profile are not identical, but no controlled comparison of the two on the same fruit is in general circulation.