The Oil-Pressing Windmill: Crushing Seeds Instead of Grinding Grain
Not every windmill on a riverbank or polder dike was built to make flour. Across the Netherlands, and above all in the Zaanstreek north of Amsterdam, hundreds of windmills were purpose-built for a different industrial task: crushing oilseeds and pressing out their oil. Linseed, rapeseed, hemp seed and walnuts arrived by barge and seagoing ship, and these mills turned them into oil for lamps, paint, soap and cooking, powering one of preindustrial Europe's most valuable trades using nothing but wind.
Two Different Jobs for a Windmill
A flour mill has one job: grind dry grain between a fixed bedstone and a rotating runner stone until it becomes fine, even powder. The grain is brittle and largely free of oil, so grinding alone does the whole job. An oil mill had to do something considerably more complicated. Oilseeds are small, dense with oil, and often quite hard-shelled, and simply grinding them into flour would not release much of the oil locked inside their cells. Millers who worked with oilseeds instead built machinery that combined crushing, gentle heating and heavy mechanical pressing into one continuous sequence, all driven by the same rotating sails and windshaft that powered an ordinary grain mill. The result was a building that could look almost identical to a flour mill from the outside, a tower or smock mill with sails turning in the wind, while containing a completely different set of machines inside: crushing rollers, heating kettles, pressing bags and huge wooden stamps.
Edge-Runner Stones: Crushing Rather Than Grinding
The first stage of oil milling used edge-runner stones, sometimes called a kollergang, rather than the flat horizontal stones of a flour mill. These were heavy stone or iron wheels standing upright on their edge, rolling around and around a circular trough as the windshaft turned them through a train of gears below the cap. Instead of pulverizing the seeds into a fine powder, the rolling weight of the stones cracked open the seed hulls and crushed the kernels into a coarse, oily pulp, sometimes called groats or meal. This crushing action mattered enormously: it ruptured the tiny oil-bearing cells inside each seed without fully atomizing the material, leaving a pulp from which oil could later be squeezed out mechanically. This crushed material still needed further treatment before any oil could be separated from it, which is exactly where the oil mill diverged furthest from a conventional grinding mill, and where the miller's real skill and experience came into play, judging by touch and smell when the meal was ready for the next stage.
Heating, Bagging and Stamping the Oil Free
Once the seeds had been crushed, the pulp was usually warmed over a fire or in a heated kettle, which made the oil inside it flow more freely and made pressing far more effective than working with cold meal. The warmed meal was then packed into strong bags, traditionally made of horsehair or coarse hemp cloth, chosen because they could withstand enormous pressure without bursting or tearing. The packed bags were placed under heavy wooden stamps or beaters, essentially massive timber blocks lifted and then dropped in rapid, repeated sequence by cams mounted on a shaft connected to the windshaft's gearing. As the stamps pounded down again and again, oil was squeezed out of the bags and ran down into collecting troughs and vats below, while a firm, flattened cake of crushed seed residue remained trapped inside the bag. Later mills, and mills built for finer or more delicate oils, sometimes used large wooden or iron screw presses instead, turning the same rotary motion into a slower, steadier squeezing force rather than repeated hammer blows. Either way, the underlying principle stayed the same across the whole industry: crush first, then press, converting the mill's rotary wind power into a hard, repetitive pounding or squeezing motion that no simple grindstone could ever produce.
The Zaanstreek as an Industrial Landscape
Nowhere concentrated this industry as densely as the Zaanstreek, the flat cluster of villages strung along the Zaan river just north of Amsterdam. From the seventeenth century onward this windy, low-lying region became a genuine industrial landscape built almost entirely around wind power, with mills constructed not only for oil but also for sawing timber, grinding dyes and pigments, hulling rice and barley, and processing paper pulp. Oilseeds such as rapeseed and linseed were shipped in from the Baltic region and other grain-growing areas, unloaded straight onto the mill's own dock, then crushed and pressed inside the Zaan mills before the finished oil was shipped onward and exported across Europe. A number of these historic mills survive today, carefully restored and in several cases still fully operational, including preserved oil mills at the open-air museum of Zaanse Schans, where visitors can watch the edge-runner stones turn and the stamping mechanisms pound away much as they did centuries ago, filling the mill with the same rhythmic thudding that once defined the whole region.
Linseed, Rapeseed and Walnut: What the Mills Produced
The seeds fed into these mills were chosen specifically for the oils they yielded, and each had its own uses downstream. Linseed, the seed of the flax plant, produced linseed oil, a slow-drying oil that became essential to traditional oil paint, varnish and putty, prized by painters and craftsmen for centuries and still valued for exactly the same qualities today. Rapeseed, also known as colza, gave an oil that was widely burned in household and street lamps before the arrival of cheaper mineral oils, and was later refined further for cooking once processing methods improved. Walnuts, hemp seed and various other oil-bearing seeds and nuts were pressed as well, each yielding an oil suited to a particular purpose, from fine art materials and lamp fuel to soap-making and cooking. The specific seed being processed determined how the mill was tuned, how long the meal needed heating, and how firmly the stamps or press needed to bear down, so an experienced miller effectively ran several different recipes through the same machinery depending on what had just arrived by boat.
Nothing Wasted: The Press Cake
Oil milling produced a valuable byproduct alongside the oil itself, and very little of the original seed was ever discarded. After pressing, the flattened, oil-depleted disc of crushed seed left behind, known as press cake or oil cake, was far from a waste product to be thrown away. It was sold on as a nutritious livestock feed, still rich in protein even after most of the oil had been squeezed out, or spread on fields as fertilizer to enrich farmland. This meant a single oil mill's output supported two entirely separate parts of the rural and industrial economy at once, feeding both the trades that needed oil for paint, light and cooking, and the farms that needed feed and fertilizer, all extracted in stages from the very same sack of crushed seeds.
Explore on the map
Windmill Worldmap plots historic windmills of every kind, from ordinary grain mills to the specialized oil-pressing mills of the Zaanstreek and beyond. Zoom into the Dutch coast to find surviving oil mills standing alongside sawmills, corn mills and drainage mills, and see for yourself how wind power once ran an entire industrial economy from a single river valley. Head to the map to start exploring.