Saving the Green in Green Vegetables
Bright green soups in Spring…or perhaps jade green pearls of peas, dark green asparagus, vibrant green dandelion leaves and young green spinach. What could be better to celebrate the season? Green simply defines Spring.
Green on the plate also makes Spring-time eating more appealing. But that lovely green vibe is not easy to preserve in cooking. Far too often, vivid green soups transform into unappetizing shades of grayish-green…and you might be left 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 result from chlorophyll. This complex molecule becomes unstable within 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 that results in a significant color change.
But it’s not as simple as avoiding that squeeze of lemon juice or few drops of vinegar until the last moment. Sure, that will help but it’s not the whole story.
Cooking – applying heat to food – weakens plant cell structures. Cook something long enough and that structure completely collapses (think really mushy broccoli). Blending a food also destroys the plant’s cell structure and exposes the molecules to air (oxidation) and any leeching acids that naturally occur in a plant. This is why a blended green soup will turn grayish-green as it cools (or cooks for a long period). There is no escape from the influence of acids even if nothing was added to the soup. Another example is something like a potato salad. Potatoes are cooked, seasoned and oil and lemon juice or vinegar is added to the sliced potatoes. To make everything tastier and more attractive, chopped chives and parsley are added. And then… Yep, those lovely green herbs change color and become drab and unattractive after only an hour or so.
So what’s the best strategy for a cook to save the green in green vegetables?
Fortunately, there are several things a cook can do to help preserve those wonderful green colors and keep Spring food vibrant:
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 chlorophyll loss and increased exposure to natural acids.
Avoid Adding Acids Until the Last Moment
This definitely helps in keeping the colors nice and vibrant. 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 here is to keep those conflicting elements apart for as long as possible.
Add Greens to Soups Last
Leaves and fresh herbs don’t take long at all to cook, so be sure to add them at the last moment – or even to the blender. Other vegetables, like asparagus, peas or broccoli are trickier. Many recipes will have you adding these vegetables early on as you cook everything together. This is a mistake. I think it is better to prepare ingredients separately. In other words, I will make the base of my asparagus soup in a large pot and blanch my asparagus separately. I combine the two elements in the blender 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. But this will also trap all the other molecules as the vegetable cooks…and one of those elements is naturally occurring acids. These will rise to the surface of the food and change the cooking environment to acidic and green colors will begin to transform. Blanching involves an open pot filled with salted boiling 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.
Add Baking Soda to Pureed Foods
Changing the cooking environment to a more alkaline situation is an old cooking trick. This will definitely keep 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 will change the flavor of your food – it will be soapy (yuck). Baking soda also promotes the breaking down of cells, meaning the plant will cook much quicker and turn to mush – granted a beautiful green mush. I only recommend adding baking soda if you know 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 still do there thing on cooked food even in a cold environment.
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