In the 1870s and 1880s, several small flour mills in southeastern Minnesota introduced important changes that laid the groundwork for a technological revolution making Minnesota's milling industry the largest in the world. Seeking to improve flour made from hard spring wheat, which was known for producing speckled flour, Minnesota millers drew on European technology to refine it by passing it through a purifier that removed specks, or middlings, and by grinding it several times. Known as the New Process, this method produced a whiter, purer flour that quickly gained consumer demand. Northfield miller Jesse Ames was among the first to experiment with the technique, using a purifier as early as 1865, and within a few years purifiers appeared at the Archibald mill in Dundas, the Mowbray mill in Stockton, the Gardner mill in Hastings, and the Faribault mill. As these changes spread through the milling industry in the 1870s, millers decided that traditional millstones, which required frequent redressing, were no longer efficient and turned instead to rollers already used in parts of Europe. One of the earliest American attempts at roller milling took place in 1872-73 at the Mowbray mill, where four-foot marble rollers were installed, and soon most Minnesota millers had replaced old millstones with more efficient porcelain-covered or iron rollers.