Saving the Green in Green Vegetables

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 revitalizes my spirit.

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 that leaves one wondering how that happened.

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

Most people know 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 causes significant changes to 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 (think overcooked broccoli). Blending foods does exactly 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 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 fragility of green colors in food. Potatoes are cooked, seasoned with oil, then lemon juice or vinegar is added to the 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.

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

1. 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 of time, causing chlorophyll loss and increased exposure to natural acids.
2. 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.
3. 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 are using a blender. Other vegetables, like asparagus, peas or broccoli are trickier. Many recipes instruct you to add these vegetables early on in a preparation to 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 right away or cool it as fast as possible.
4. 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 florets of broccoli in salted water and compare the color to steamed broccoli.
5. Add Baking Soda to Pureed Foods: Changing the cooking environment to an alkaline environment is an old cooking trick. This technique keeps green vegetables green, but you need to be cautious. Only a small amount of baking soda is needed — something like a knife tip for a couple 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, like I instruct in the two soup recipes below.

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

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