Depending on how good you are, it takes somewhere between fifty minutes and an hour to [grind] enough maize for tortillas for one person. That means for a family of five someone is going to be spending four or five hours a day doing nothing but grind. It’s very exhausting, grinding. ...
That kind of labour-intensive grinding was what they did in Ur, and in ancient cities of the Middle East and Egypt. By the time you get to Rome, roughly—by about the birth of Christ—in the Middle East and in Europe, they get a rotary grindstone, and instead of requiring one person per every five to spend all day grinding this two pounds of grain that everybody in the city needs, they get it down to one in thirty. Then they get watermills and it goes down to one in three hundred—and nowadays we don’t even think about it! There are big steel rollers up there in Minneapolis and they’re grinding grain for hundreds of thousands of people, using just a handful of workers.
Now why didn’t Mexico do that? Was it just backward? Why didn’t it move to other forms of grinding? The trouble is if you grind wet, you cannot use these other rotary grindstones. So even if the Mexicans had had them, they couldn’t have used them. When the Spaniards came here they brought rotary grindstones, but you just can’t grind wet maize with rotary grindstones. And if you want tortillas—which we now know have nutritional advantages, but they are also a flexible bread, and hence more appealing than the kind of porridge-y things or tamales that you would have otherwise—you have to grind wet. ...
Therefore, in Mexico, right up until about twenty years ago, large numbers of Mexican women were spending five hours a day grinding.
She goes on to explain how the capital-subsitution finally came about. But it's still not without its costs:
A machine-made tortilla is not anything like a homemade tortilla – it’s not even in the same universe. Mexican women that I have talked to are very explicit about this trade-off. They know it doesn’t taste as good; they don’t care. Because if they want to have time, if they want to work, if they want to send their kids to school, then taste is less important than having that bit of extra money, and moving into the middle class. They have very self-consciously made this decision. In the last ten years, the number of women working in Mexico has gone up from about thirty-three percent to nearly fifty percent. One reason for that—it’s not the only reason, but it is a very important reason—is that we’ve had a revolution in the processing of maize for tortillas.And a different view: there may actually (*shock*) be some good from removing the tortilla subsidies in terms of market development:
One of the negative effects of having had tortillas subsidized for so long in Mexico—which has really aided the poor—is that nobody has wanted to invest huge amounts of money into developing better tortilla machines and flour mills and things. Now, maybe, we’re at a point where we’re developing a boutique market for good tortillas.
And comments on technology exchange - really it's a wonderful discussion:
What happened was that European techniques—wheat mills and bread-baking, for example—came to Mexico, but what Mexicans knew about how to process food did not go to the Old World. The process of adding alkali to maize and grinding it wet didn’t go. The Europeans ground maize like they ground wheat, and they got pellagra, and they went blind, and they died.
The technique of dehydrating chiles and grinding them and rehydrating them to make some of the healthiest sauces in the world has never moved out of Mexico. It hasn’t even got to the United States, for goodness’ sake....