Why Tomato Sauce Is Prone To Splattering

Whether you're preparing some homemade all-purpose tomato sauce or popping open a jar of store-bought marinara, you're no stranger to what happens when this easy pasta pairing bubbles up — it splatters. Maybe it's to the point where you only heat it on the stove with the lid on or place a covering over it in the microwave when you heat it up. But why is it that other liquids, such as water, don't have this problem, yet every time you leave tomato sauce uncovered, there's a small volcanic eruption? It has to do with viscosity — put simply, tomato sauce literally erupts due to the force underneath the bubbles.

Viscosity is measured by how much friction there is between molecules. The more viscosity a liquid has, the more internal friction it has. Tomato sauce, which is a dense liquid, has molecules with more friction. So, when heat tries to escape, those molecules aren't so quick to get out of its way. The result of higher viscosity in tomato sauce is increased force on the molecules until, finally, that heat breaks through the surface. And boom, you have a mini explosion as your tomato sauce ends up splattering all over your stove. By comparison, water has very low viscosity. When it heats, its molecules move without issue, so the heat bubbles up to the surface with ease, escaping without incident. This explains why boiling water never splatters. The molecules within tomato sauce just have greater internal friction than water, but luckily, there are still ways to reduce tomato splatter.

You can't argue with science, but you're also not doomed to a kitchen full of splatter every time you make tomato sauce. Of course, the easy way to avoid this problem is to cover your sauce with a lid as it heats. But if you're trying to thicken the tomato sauce without changing the flavor and want some of that water to evaporate, then this isn't an option. Instead, try letting your sauce come to a small simmer on the lowest heat. This will prevent too much heat from forcing its way through the surface, and ultimately limit the splattering. 

It also doesn't hurt to use a deeper pot, where the splatters won't make it outside the pot's walls. You can also cover the pot as much as possible but still create a small vent for steam to escape, which will help control the splatters.