There's a parallel with grains: staples like rice and wheat are more legible to states than other alternatives like legumes, tubers, and starch plants, even though the latter were comparable in terms of calories generated by unit labor. E.g. many roots are buried and hidden from tax collectors. States which enforced cultivation of the legible grains had a greater tax base and outcompeted those that didn't.
> E.g. many roots are buried and hidden from tax collectors.
Those roots tend to be attached to green stuff that's above ground and very visible. Why should that be any less legible to tax collectors than wheat or rice?
It's a combination of factors. Cereals like wheat and rice tend to ripen seasonally and simultaneously. They do so visibly, and must be harvested soon after. So a state sends its tax collectors around when the grains are ready to be harvested, and the amount that was generated is immediately visible. They also keep well: tubers go bad relatively quickly (and can be kept underground until actually needed for consumption), while rice and wheat can be transported over long distances and times with an order of magnitude less loss.
Consider the case of the Incas. As a civilization, they relied on two crops for calories and nutrition: maize and potatoes. Despite that, efforts at taxation primarily focused on maize, because it was so much better suited for taxes and commerce (though they did eventually invent a way to freeze dry potatoes).
I think you're wrong to assume that of two things that co-evolved, one thing had to cause the other.
Interestingly, per https://acoup.blog/2022/07/29/collections-logistics-how-did-... several Mediterranean cultures equipped their soldiers with handmills, with the Romans also including sickles so they could process grain from the fields they were marching near, allowing an earlier campaign season then were they forced to wait for it to be harvested.
https://en.wikipedia.org/wiki/Quern-stone#Laws_against_use
Laws against a thing often indicate that it was enough of a thing to be a problem, although there are exceptions.
For those without access to windmills, the daily grind would produce flour/ meal for that day.
I think you’re mixing cause (larger windmills are more efficient, making it a win to centralize them) with effect (that makes it easier to tax flour production).
If that were the main reason, we would have stories about people clandestinely milling at home. I’m not aware of any.
(I also think, but am not sure, milling already was centralized before the introduction of wind power)