During a recent holiday in California, my wife and I came across an historic preserved grist mill. On a broiling afternoon, the comparative coolness of the interior of the old buildings was very welcome, as was the guided tour and demonstration by the volunteer miller. As well as explaining the machinery, he talked about the social history of milling. The miller often had high social status in his local community because he controlled one of its most important services and because he regularly met almost everyone in the neighbourhood. He illustrated the central place of the mill in local life through some of the many proverbs and idioms which he suggested had their roots in the miller’s trade.
For example, to have a millstone around one’s neck is a graphic reference to the heaviest, most intractable object that anyone in a village would ever encounter. To be put, or to go through the mill means to be exposed to hardship or rough treatment, just like corn being ground (the first citation in OED2 is from 1818, but it surely must be older in the spoken language). The proverb all is grist for the mill, meaning “everything can be made useful, or be a source of profit” illustrates the word grist, “a quantity of corn to be ground” (it derives from an Old English word from which we also get “grind”). The miller ground whatever was brought to him, and charged for the grinding, so all corn arriving at the mill represented income for him, regardless of its quality. Again, this is first attested in the sixteenth century, but is probably much older. The term grist mill was once common in the USA as it was in Britain to describe a mill open to all comers, who brought their batches of grain, or “grists”, to be ground. OED2 quotes the West Somerset Word-book of 1886:
The small mills for grinding people’s own corn, all over the country side are always called grist-mills.
Our guide (I never did discover his name) then gave an explanation of the proverb keeping your nose to the grindstone. The most important possessions of the miller were his pairs of grindstones, which were incredibly expensive. They had to be made of just the right kind of stone, which was not usually to be found in the neighbourhood, and the cost of transporting such weighty and unwieldy objects was the largest part of the expense of setting up a mill (the ones in the mill we visited apparently came from France, but this would be an exceptional case). The lower stone was fixed and the upper one turned by the machinery (driven by a waterwheel in this case). The stones had to be set exactly the right distance apart: too big a gap and the corn didn’t grind properly; too small and the grain overheated and began to burn. Gauging the gap was a crucial part of the skill of milling, not least because accidentally allowing the stones to touch would within a very short time wear them out. But setting the gap correctly was complicated by the need to keep the stones completely enclosed, so as to minimise flying dust and to keep the flour free from dirt, which meant their position could not be judged by eye. Our guide was adamant that the best tool the miller had was his nose: he would immediately be able to detect the slightest trace of burning and adjust the gap before any harm was done. But to do this effectively meant the miller had to stay constantly close to the stones — hence, keep his nose to the grindstone.
The trouble with this explanation, plausible though it sounds, is that it doesn’t fit the evidence. All the standard reference works say that the type of grindstone referred to in the proverb is the smith’s one for putting an edge on a metal tool. The original form of the expression was to hold one’s nose to the grindstone and the first example quoted in OED2, from John Frith’s A Mirrour to Know Theyself of 1532 is:
This Text holdeth their noses so hard to the grindstone, that it clean disfigureth their faces.
which quite clearly refers to sharpening tools, not to the miller’s trade. Subsequent citations confirm this.
Another phrase he mentioned that sounds as though it originates in the corn mill is run of the mill, meaning “undistinguished; ordinary, average”, perhaps referring to the ungraded output of the grinding process. But as the miller ground in batches whatever came to him and gave the resulting flour back to his customer, there was normally no question of separating it by quality. In fact, the expression is modern (OED2’s first citation is dated 1909), and it seems to refer to the unsorted output from a textile mill. Another form of about the same date was run of the mine, with a similar sense concerning ore.
What this shows is that one should never jump to conclusions about the origins of expressions, and that anecdotal or plausible-sounding explanations (with due deference to our guide) are always to be distrusted unless backed up by evidence.