Children point at it before they can name it. Something about a round brick building wearing a tilted white hat suggests that the building is up to something, and for once the suggestion is correct. The hat is not decoration. It is the last working part of a machine.
An oast house — a hop kiln, if you were being plain about it — existed to dry hops. Freshly picked hops are green, damp and perishable, roughly four-fifths water, and a brewer wants them dry, stable and still aromatic. Get that wrong and a year of a farm's work turns to mould in a fortnight. So the crop went straight from the garden to the kiln, usually within hours.
The layout is beautifully simple. At the bottom sits the fire, historically charcoal or anthracite, chosen because it burns cleanly enough not to taint the crop. Above it, a slatted drying floor is spread with a deep, even layer of hops, and above that rises the tapering roof. Heat travels upward through the hops, carrying the moisture with it, and the whole cone acts as a chimney with a job to do. The drying man's skill lay in the layer's depth, the fire's steadiness and knowing when to stop; too fierce and the hops scorch, too slow and they spoil.
Then the cowl. A cone can only draw properly if the air leaving the top is not being shoved back down it by the wind, so the cowl is fitted with a vane and turns on the wind's own instruction, keeping its opening on the sheltered side. It is a weather vane that works for a living. When it swings round on a gusty afternoon it is not being picturesque; it is adjusting the draught.
That the South East is full of them is a matter of hops rather than taste. Kent and the Sussex Weald grew the country's hops in quantity through the nineteenth century, and where hops were grown they had to be dried on the spot. Whole villages filled with Londoners at picking time. The kilns went up in twos and threes, and their silhouettes settled into the skyline so thoroughly that the shape now reads as regional identity rather than industrial plant.
Most stopped drying long ago. Hop acreage fell, drying consolidated, and the kilns became stores, then problems, then — where somebody was stubborn enough — houses with unreasonably round rooms and no straight walls to hang a picture on. The conversions vary from tactful to unfortunate. The cowls survive at very different levels of honesty: some turn, some are bolted still, and a good number are fibreglass.
Ours turns. The Oast at Martins Farm is a single-kiln building at the top of the yard, and its cowl still moves with the wind, which guests notice from the lane before they have parked. We make no claim about what was dried here or by whom; the census sheets and the 1875 survey tell us the building was an oast and that the estate did the ordinary work of the Weald. That is enough. The mechanism is intact, the shape is unaltered, and on a blustery evening you can stand in the yard and watch a piece of Victorian engineering quietly do the only thing it ever wanted to do.
It is a weather vane that works for a living. When it swings round on a gusty afternoon it is adjusting the draught.