Stock is the main liquid most often used to simmer and cook the rice. It could be vegetable, chicken, beef, seafood or another type, depending on what type of risotto you’re making. Always warm stock before adding it to the risotto as that will help maintain a consistent cooking temperature. Add the stock slowly to the risotto, about half to one cup at a time, simmering it until almost fully absorbed by the rice before you make the next addition.