Liquid is simmering when it reaches a temperature between 185°F - 195°F and tiny bubbles form that gently rise and collapse just below the surface. Simmer is used for reductions, soups and stews. If your sauce is sputtering out of the pan you are not in the simmer mode, you are close to boiling. Turn down the heat, stir the contents of the pot and check frequently so the bottom of the pot and the contents do not burn.