The science-backed trick to the silkiest, greenest broccoli soup ever

Most broccoli soup recipes don't exactly scream “vibrant” or “green.” In fact, I bet most people know it better cream of broccoli soup, or its cheesier cousin, Broccoli Cheddar Soup. This soup subverts those expectations: a luscious, bright green broth that's just as rich and velvety (but without the dairy), a perfect bite of charred broccoli, melted leeks, and crunchy, tender peas. It's particularly well-suited to the 'shoulder' seasons – the time after summer or before spring when the temperature is neither too hot nor too cold, but perfect for greens like spring onions, peas and of course broccoli.

But making a perfectly smooth broccoli soup without dairy can be tricky. Fibrous broccoli is a challenging ingredient in pureed soups with its many textures. In order to achieve a silky, creamy texture, it is important to cook the broccoli thoroughly, until it is soft and broken; Unfortunately, broccoli cooked at this temperature often loses its bright green color as the chlorophyll breaks down over time and heat, making it pale and unappetizing. So how do we get a creamy texture while keeping that attractive green color? We use the power of pH.

Seeing Green: How to improve baking soda in soup

In my article, I wrote at length about how pH can affect cooking vegetables. When dissolved in water, baking soda acts as a weak base, raising the pH value of the water. If the pH of the blanching water is higher (about 8.5), the breakdown of chlorophyll is slowed and more green hues remain in vegetables such as broccoli. In addition, sodium bicarbonate specifically reacts with chlorophyll to form chlorophyllin, a bright green salt derivative of chlorophyll. (Chlorophyllin is made by removing a magnesium ion from the chlorophyll molecule and replacing it with sodium. This small substitution makes chlorophyllin more stable than chlorophyll. More stable means more green.)

But adding baking soda to the blanching water can be a double-edged sword: Yes, it can help preserve the green color in chlorophyll-rich vegetables. But it is also prone to mushy textures. Why? In a high pH cooking environment (say, greater than 8.0), pectin (a polysaccharide found in the cell walls of all land plants) breaks down and dissolves faster, resulting in softer, more tender textures as the cell walls break down more easily. .

Generally speaking, this clutter can be a bad thing. But for pureeing the soup, the pulpiness is perfect! The resulting puree is velvety, smooth, without a hint of stringiness. And because the addition of baking soda to the cooking water increases the rapid breakdown of pectin, it also dramatically reduces cooking time—shaving a few minutes off the ten minutes it would take in otherwise pH-neutral water without baking soda.

Once the green puree has been properly mixed and mixed back into the final soup, it is important to heat the soup until it is heated through and then remove it from the heat. This will preserve the bright green color of the soup.

Even greener: build up the flavor with even more green vegetables

While broccoli is abundant in chlorophyll, its sulfurous flavor can be a bit overwhelming and one-dimensional. To tone down the flavor, I add more chlorophyll to the mix by blanching the tops of the green leeks and parsley in the same pot before tossing it all in with the broccoli. In addition to the bright color, this intense green puree gives the soup much of its body and texture.

Finishing touches

At this point, there is a lot of vegetable flavor in the puree. But for richness and depth, I make a broth base with leek protein, garlic, fish sauce and a spoonful of broth noodles. These sources of umami add meatiness to the soup without adding much (if any) meat. For textural contrast, I slice extra broccoli florets into the soup and fold in the hot peas at the very end for a nice crunchy delicious crunch. The finished soup is juicy, velvety, smooth and, above all, spectacular. It probably has enough green vegetables for an entire week – which is always a plus.

Cooking method
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