The Science-Backed Trick for The Silkiest, Greenest Broccoli Soup Ever

Most broccoli soup recipes don’t exactly scream “vibrant” or “verdant.” In fact, I’d wager that most people are more familiar with cream of broccoli soup, or its cheesier cousin, broccoli cheddar soup. This soup subverts all of those expectations: A luscious, bright green broth that’s just as rich and velvety (but without the dairy), dotted with perfect morsels of charred broccoli, melted leeks, and crisp-tender snap peas. It’s particularly well suited to the “shoulder” seasons—the periods after summer or before spring, when temperatures are neither too hot or too cold, but perfect for green crops like spring onions, peas, and of course broccoli.

But making a perfectly smooth broccoli soup without relying on dairy can be tricky. Fibrous broccoli with its multitude of textures is a challenging ingredient for pureed soups. For a silky, creamy texture, it’s important to cook broccoli thoroughly, until it’s soft and broken down; unfortunately, broccoli cooked to this degree often loses its bright green color as chlorophyll breaks down over time and exposure to heat, turning pale and unappetizing. So how do we get a creamy texture while keeping that attractive green color? We leverage the power of pH.

Seeing Green: How Baking Soda Enhances the Soup

I’ve written at length in my article on how pH can affect vegetable cooking. Baking soda acts as a weak base when dissolved in water, raising the pH of the water. When blanching water has a higher pH value (around 8.5), chlorophyll degradation slows, retaining more of the green hue in vegetables like broccoli. Additionally, sodium bicarbonate in particular reacts with chlorophyll to form chlorophyllin, a bright green salt derivative of chlorophyll. (Chlorophyllin is produced by removing a magnesium ion from the chlorophyll molecule and replacing it with sodium. This small substitution makes chlorophyllin more stable than chlorophyll. And more stable means more green.)

But adding baking soda to blanching water can be a double-edged sword: Yes, it can help retain the green color in chlorophyll-rich vegetables. But it also tends to lead to mushy textures. Why? In a high-pH cooking environment (say, greater than 8.0), pectin (the polysaccharide found in the cell walls of all land plants) breaks down and dissolves more quickly, leading to mushier, softer textures as the cell walls fall apart more readily.

In general, that mushiness can be a bad thing. But for the purposes of pureeing to make a soup, mushiness is perfect! The resulting puree is velvety, smooth, without a hint of fibrousness. And because adding baking soda to the cooking water enhances that rapid breakdown of pectin, this also reduces the cooking time dramatically—shaving off a few minutes from the ten minutes otherwise required in neutral pH water without added baking soda.

Once the green puree is properly blended and mixed back into the final soup, it’s important to heat the soup until just warmed through and to then remove it from heat. This will preserve the soup’s vibrant green color.

Even More Green: Build Flavor with Even More Green Vegetables

While broccoli is plenty rich in chlorophyll, it can be a bit overpowering and one-dimensional in its sulfurous flavor. To temper that flavor, I add even more chlorophyll to the mix by blanching green leek tops and parsley in the same pot before blending it all together with the broccoli. In addition to vibrant color, this intensely green puree also provides most of the soup’s body and texture.

Finishing Touches

At this point, there’s plenty of vegetal flavor in the puree. But to bring richness and depth, I build a brothy base with leek whites, garlic, fish sauce, and a sneaky spoonful of bouillon paste. These sources of umami lend a meatiness to the soup, without adding much meat (if any at all). For textural contrast, I char extra broccoli florets to serve in the soup, and fold in snap peas at the very end for a welcome crisp-tender crunch. The finished soup is savory, velvety, unctuous, and above all, visually striking. It’s also probably got enough servings of green vegetables for an entire week—which is always a plus.