What an incredible load of made up waffle. It's very obviously some first year student's thesis...
Why would any sane person, go to such trouble to make such an item, from stone, and to such a fine level of accuracy, simply to mash beer? It defies any belief. If such a shape of object were needed, then they had copper-smith technology, the ability to make such items from copper, and copper would work brilliantly. The only reason he could think of for not using copper, was that copper would be a similar colour to the mash, and not so easy to distinguish.
Come on, you can do better 0/10.