Why Does Tomato Sauce Spatter as It Boils?

published May 15, 2015
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(Image credit: Leela Cyd)

There’s nothing better than a homemade tomato sauce, but nothing worse than having to clean splashes of tomato off the backsplash or the wall behind the stove. So, what makes tomato sauce so explosive?

What’s in Tomato Sauce?

Tomato sauce is a thick fruit mixture made up of water and also chunks of crushed tomato fruit and/or purée with all the natural sugars, acids, fiber, pectin, etc. from the fruit.

What’s most interesting about tomato purée is that, if it is held at room temperature for long enough, pectin enzymes in the fruit will begin to break down the cell walls in the fruit, breaking open the cells and thickening the purée. This is also why ripe tomatoes are softer and more fragile; those same enzymes have essentially begun to digest the tomato cell walls, softening the structure of the tomato fruit.

Tomato Sauce Spattering: It’s a Matter of Viscosity

When water boils, water is fluid and free-moving enough that when gas bubbles form as water evaporates, those bubbles can move freely through the water and easily rise to the surface with little resistance.

On the other hand, tomato sauce is more than just water; there’s a lot going on in a pot of simple tomato sauce with all that pulp, fiber, and sugar that leads to a liquid that is thick and not so free-flowing as water, and therefore more viscous.

When tomato sauce boils, again, gas bubbles form and want to escape to the surface, but those gas bubbles meet a lot of resistance. The pressure builds up below the surface until finally those gas bubbles can break through to the surface, erupting upward and pulling globs of sauce with them. The result is splashes of tomato sauce flying out of the pot.

How to Avoid Spattering

The easiest option is to keep the sauce cooking on a lower heat setting. This won’t eliminate the splashes, but at least it will reduce their number and frequency. Another option is to stir, which will help push those gas bubbles to the surface faster and minimize the pressure buildup.

Do you have any tips or tricks to help minimize the spatter when you cook tomato sauce?