Cooking Tips

For the Best Broccoli Soup, Overcook the Broccoli

Forget what you’ve been taught about overcooking vegetables.

Published Sept. 24, 2021.

How often does broccoli-cheese soup actually taste like broccoli? Not often. For her Broccoli-Cheese Soup recipe that appeared on the America’s Test Kitchen TV show, Cook’s Illustrated test cook Andrea Geary was determined to bring back the broccoli.

Upping the amount to an impressive 2 pounds was a start. But to truly make it the star of the show, Andrea used a technique introduced by culinary icon (and vegetable-cookery legend) Alice Waters. That technique: cooking the living daylights out of it.

In her book The Art of Simple Food (2007), Waters instructs home cooks to sauté broccoli florets and stems in butter, add some water, and then simmer them covered on the stovetop for a full hour. A full hour. Doesn’t that overcook the broccoli? It does. Overcooking it is actually how you coax out the best flavor.

Here’s the science behind it: When moist heat breaks down the broccoli's cell walls, it triggers the formation of sulfur-containing compounds called isothiocyanates. The longer the broccoli is cooked, the more these compounds are produced and the more pungent the broccoli's taste—but only up to a point. With really prolonged heating, the isothiocyanates break down into less pungent compounds, the most volatile of which eventually evaporate.

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Sure enough, this overcooked broccoli made the best-tasting soup: sweet, caramelized, and nutty. But Andrea also decided that spending an hour minding a pot of broccoli for a simple soup wasn’t the most efficient use of time. To speed it up, she added a small amount of baking soda. This accelerated the breakdown of the broccoli’s cell walls and more quickly transformed the sulfurous compounds into more pleasant ones so that the simmering step took only about 20 minutes.

So the next time you cook Broccoli-Cheddar Soup, forget what you’ve been taught about overcooking vegetables. Your soup will taste better because of it.

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