Romano vs Parmesan in Cacio e Pepe? I've tried making Cacio e Pepe a few times, using a recipe from America's Test Kitchen. In Cacio e Pepe, you boil pasta in a limited amount of water, then mix some of the hot starchy water with grated pecorino Romano cheese. The cheese melts/dissolves in the water to form a cheesy liquid which is poured over the pasta.

I've had good luck doing this with Romano, even using domestic cow's milk Romano. But one time I was short on Romano, and tried using about 1/4th Romano and 3/4ths imported Parmesan. When I added the starchy water, some of the cheese dissolved--the Romano, I assume--but most of it coagulated into a gooey, stretchy mass.

What is the difference between Romano and Parmesan, that would make them behave so differently when mixed with hot, starchy water? Are there other similar cheeses--asiago for example--that would work well in this recipe?
The difference between Pecorino Romano and Parmiggiano Reggiano (Parmesan) is that the first is made from sheep milk, the last from cow milk.I think this is the reason that they behave so differently, because they are made from milk of very different animals.The closest type of cheese to the pecorino romano might be the pecorino sardo.