I consulted several sources, from my culinary school notes to the recently released tome The Fundamentals Techniques of Classic Italian Cuisine. The best explanation I found is that cooking is improved and proceeds more swiftly if all the risotto ingredients are the same temperature. Essentially, adding cold broth to a hot pan of cooking rice will cool everything down, whereas keeping a constant cooking temperature keeps everything moving along at the right pace.
This answer feels a little unsatisfactory to me. Risotto is usually cooked in a wide pot and the broth is being added in incremental cups—the relatively small dip in temperature from this relatively small amount of broth spread over the surface of the pot just can't make that huge of a difference. Maybe it does in the precise and demanding environment of a restaurant kitchen, but when we're just making risotto for ourselves in a home kitchen? In this case, I'm inclined to think that warm broth is of less vital importance.
What do you think? How do you make risotto?
Related: How to Make Great Risotto at Home
(Image: Emma Christensen)