Saving the Green in Green Vegetables
Bright green soups in spring…yes please. Maybe some jade green pearls of peas on your plate or dark green asparagus. And let’s not forget about brilliant green dandelion leaves and young spinach. Is there a better way to express the season on a plate or in a bowl? Green just defines spring.
Green food makes spring-time eating more appealing.
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 leave you 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. This complex molecule becomes unstable in the plant’s cell structure when it is exposed to acidic conditions. The acids attack magnesium atoms and replace them with hydrogen — a simple transformation resulting in significant color change.
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.
Cooking — applying heat to food — weakens plant cells. Cook something long enough and the structure collapses (think really mushy broccoli). Blending foods accomplishes the same basic result. The plant’s cell structure is destroyed and molecules are exposed to air (oxidation) and leeching acids that naturally occur in the plant. This is why blended green soups turn grayish-green as it cools (or cooks for a long period). There is no escape from this acidic influence to green colors, even if nothing was added to the preparation.
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 green vegetables?
Fortunately, there are several things you can do to keep spring food vibrant…and green:
Keep Cooking Times to a Minimum: Robust vegetables like broccoli and asparagus require only 5–7 minutes to fully cook (sometimes less time if the vegetable is prepared in smaller pieces). Fragile leaves, like spinach, only need a few seconds to wilt. Longer cooking times expose the vegetable to air for longer periods of time, causing chlorophyll loss and increased exposure to natural acids.
Avoid Adding Acids Until the Last Moment: This helps to 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 to 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 are using a blender. Other vegetables, like asparagus, peas or broccoli are trickier. Many recipes will 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.
Blanch Vegetables Instead of Steaming: I’m not anti-steaming…just to be clear. But when it comes to green vegetables, there is 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 involves 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 salt that is slightly alkaline, causing food to remain green longer — unless you overcook it. You can test this yourself rather easily. Blanch a few florets of broccoli and compare the color to steamed broccoli.
Add Baking Soda to Pureed Foods: Changing the cooking environment to an alkaline environment is an old cooking trick. This cooking trick keeps green vegetables green, but you need to be cautious with this method. Only a very small amount of baking soda is required — something like a knife tip for a couple liters of water. Adding too much baking soda changes the flavor of your food — it will become 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 adding baking soda only when the final process is blending the food.
The bottom-line here is to cook your greens rapidly, avoid adding any additional 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!
