Keeping Green Vegetables Green

My tips on preserving vibrant green colors in cooked food, plus two delicious green spring soup recipes.

Mar 18, 2024

I first published this article in March of 2022. This version is updated to make a couple of changes in the recipe, and to clean up some prior editing mistakes...plus, I have a much broader audience now, which means many subscribers probably never saw the original publication.

Freshly-made silken tofu with a plate of greens ¦ Photo by Jack McNulty

I want bright green soups in spring. And yes, I also want little green pearls of peas on my plate—and dark green asparagus. And I don’t want to forget about brilliant green dandelion leaves and young spinach.

I can’t think of a better way to wipe clean the dull stains of last winter than filling my plate or bowl with vibrant green food; it regenerates my spirit like a new branch emerging from a dormant tree.

But here’s the problem: That lovely green vibe is not easy to preserve. Far too often, bright green soups turn into unappetizing shades of grayish green, leaving one wondering how that happened.

The answer is all about acids — either naturally present in the vegetable or added during or after cooking.

Most people know that green vegetables are a result of the plant’s natural chlorophyll. Exposing the plant to acidic conditions creates a chain reaction in the cell structure, and magnesium atoms are replaced with hydrogen atoms—a simple transformation that significantly changes the plant’s color.

But it’s not as simple as avoiding that squeeze of lemon juice or a few drops of vinegar until the last moment. Sure, that helps, but it’s not the whole story.

When heat is applied to plants, the cell structure weakens. Cook a plant long enough, and the structure collapses and turns mushy (feel free to insert your overcooked broccoli memory here). Blending foods does precisely the same thing. Two crucial interactions occur once the plant’s cell structure is destroyed through the blending process – the molecules oxidize and become exposed to the leeching acids that naturally occur in the plant. This is why blended green soups often turn grayish green as the soup cools (or cooks for extended periods).

A simple potato salad offers another example of the fragile nature of green colors in food. Potatoes are cooked and seasoned with oil, then lemon juice or vinegar is added to the warm potatoes. Chopped chives and parsley are added to the salad to make everything tastier and more attractive. And then…yep, those lovely green herbs change color and turn into a drab and unattractive salad after only an hour or so.

A plate of quickly blanched snap peas ¦ Photo by Jack McNulty

So, what’s the best strategy to preserve those attractive green colors in vegetables? Luckily, you can do several simple things in the kitchen to keep spring food vibrant and green. Here are five of my favorite techniques:

Keep Cooking Times to a Minimum: Robust vegetables like broccoli and asparagus require 5–7 minutes to fully cook (sometimes less if the vegetables are prepared in smaller pieces). Fragile leaves, like spinach, only need a few seconds to wilt. Longer cooking times expose vegetable leaves to air for longer periods, causing chlorophyll loss and increased exposure to natural acids.
Avoid Adding Acids Until the Last Moment: This simple step helps keep colors nice and bright. A splash of lemon or vinegar is often perfect to balance flavors. Just keep the timing in mind and add the acids at the end of the cooking process, or add the greens at the end. The bottom line is this…keep those conflicting elements — greens and acids — apart for as long as possible.
Add Greens to Soups Last: Leaves and fresh herbs don’t take long to cook, so be sure to add them at the last moment — even if you use a blender. Other vegetables, like asparagus, peas, or broccoli, are trickier. Many recipes instruct you to add these vegetables early in the preparation and cook everything together. This is a mistake. I think it is better to prepare your ingredients separately. In other words, I make the base of my asparagus soup in a large pot and blanch the asparagus separately. I combine the two elements in the blender at the last moment and either eat the soup immediately or cool it as fast as possible.
Blanch Vegetables Instead of Steaming: Just to be clear – I’m not anti-steaming. But when it comes to green vegetables, I have a problem. Steaming requires a cover to trap the steam in the pot. Covers also trap molecules as the vegetable cooks…and one of those elements is naturally occurring acids. These acids gather on the lid, cool slightly, and fall back to the surface of the food. The cooking environment changes to acidic, and green colors begin to transform. Blanching relies on an open pot filled with boiling salted water. Here, the food cooks quickly. Natural acids that leech to the surface of the food are diluted by the large portion of water and helped by the presence of slightly alkaline salt, causing food to remain green longer — unless you overcook it. You can easily test this yourself. Blanch a few broccoli florets in salted water and compare the color to steamed broccoli.
Add Baking Soda to Pureed Foods: Changing the cooking environment to alkaline is an old cooking trick. This technique keeps green vegetables green, but you need to be cautious. Only a tiny amount of baking soda is required — something like a knife tip for a couple of liters of water. Adding too much baking soda changes the flavor of your food — it becomes unpleasantly soapy (yuck). Baking soda also causes plant cells to break down, meaning the plant will cook quicker and turn to mush — albeit a beautiful green mush. I recommend using small amounts of baking soda when the final process is blending the food, as described in the two soup recipes I share.

The bottom line is to cook your greens rapidly, avoid adding acids until the last moment, and eat your food immediately. If you are planning for leftovers and longer storage times, consider cooling the food rapidly after it is cooked and keeping elements of your recipe separate —remember, acids continue to do their thing on cooked food, even in a cold environment.

Now…go eat your greens — you’ve earned it!

This Week’s Recipes…

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Spring Pea and Wild Garlic Chowder

I like to prepare extra-vibrant and explosively tasty soups to celebrate increasingly warmer days using whatever the season offers. During the early days of Spring, plenty of wild garlic, fresh peas, and new potatoes are available, and…well, you get the idea.

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Asparagus and Pea Bisque

Asparagus soup is difficult to get right. The delicate asparagus flavor is often lost among the other ingredients – especially if the soup has a lot of fat.

I boost this soup's asparagus flavor by using green and white varieties to create balance and intensity. I think cooked white asparagus is more flavorsome than green. Using both in combination turbocharges the soup's flavor.

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Previously in this series about Alternative Grains

Be sure to join me for the next part of this series as I expand on millet and begin looking at the tiny grain teff and how it helps define Ethiopian cuisine.

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