The Milling Gear @museum.de

F: Have you been brave enough to climb the steep ladder? The effort was worth it, because you've arrived on the stone floor, where the beating heart of the mill is located. This is where the milling gear stands, with its two great millstones sitting one on top of the other, well protected by the tun, that's the round wooden casing.

M: The milling gear consists of the stationary bedstone at the bottom and the runner – that's the one on top that turns and mills the grain as it rotates. The principle is quite simple: when the sacks of grain arrive up here, they're emptied into the hopper. It directs the grain straight into the eye – the opening in the middle of the runner. As the grain is milled, the centrifugal force channels it out towards the rim of the bedstone. It makes its way between the stones, emerges at the edge, falls through a box-shaped funnel and ends up one level down, in the chute that fills the sacks. And there's your flour or meal.

F: So far, so good. But although a millstone weighs more than a tonne and a half and is basically indestructible, it doesn't carry on producing top quality results forever. If the flour starts getting too warm, it means the stone needs to be sharpened, a process known as dressing. The specific method of dressing depends on the type of grain to be milled, the mill's capacity and the degree of fineness required – in other words, coarse or fine milling. Each mill sharpened its stones to its own standard.

M: When the time for dressing came around, the wooden housing – or tun – had to be dismantled and the runner lifted off. That's what the millstone crane was used for, with its big, curved pincers. The runner has two holes in its side, where the pins at the ends of the pincers can find purchase and raise the stone. The gallows allowed the stone to be moved, flipped by 180 degrees and set down on its back, as it were.

F: That's when you realise that millstones don't lie flat on top of one another. Instead, they have furrows cut into their surface. Those furrows are subject to wear and have to be re-cut with special hammers. It takes two millstone dressers about a day to re-cut the furrows to the required depth and sharpness. Once the dressing is done, the runner can be lifted again, flipped over, manoeuvred over the bedstone and lowered back down.

M: Dressing is strenuous, detailed work, but absolutely essential! First, the raised areas known as lands are beaten flat with a bush hammer. Then the furrows are re-cut using a mill pick or bill. It's the furrows that ensure an adequate air supply as well as moving the flour or meal out towards the rim. They stop the millstones heating up as they rotate, which not only ruins the grain, but also risks setting the entire mill ablaze.