How does cooking affect the nutrients in green beans?


Green beans are a perennial favorite vegetable. They are a great addition to salads and can stand alone well as a delightful side dish to many different entrees. Yet, just like with other vegetables, the way you cook green beans can have a dramatic effect not just on their color, taste and texture but upon their nutrient content as well. Not only does the length of cooking time determine whether your beans will be bright green and crisp as compared to pale green and limp, but it also determines how nutrient rich they will be. Like with many other vegetables, shorter cooking time is key when it comes to cooking green beans.

Background on green beans

Green beans, typically referred to as string beans, are in the same family as the shell beans such as pinto, black and kidney. Known scientifically as Phaseolus vulgaris, they are referred to as “common beans,” probably owing to the fact that they all derived from a common bean ancestor that originated in Peru. Yet, when describing the nutritional profile of green beans the word “common” would not be a word you would use since they are a storehouse of many different vitamins, minerals and nutrients. That’s why the cooking them properly is so important!

The shape of green beans and the impact of cooking

Although green beans might seem like a fairly strong, hearty, and durable vegetable, this popular food is actually quite sensitive to cooking times and temperatures. The reason is simple. Compared to many other vegetables, green beans have a large surface area and a small amount of space inside. This large surface area exposes a lot more nutrients to air, light, and heat than does a smaller surface area on a vegetable that is more round in shape and has a larger space inside.

Green beans require minimal cooking

Don’t let the strong outside shell of a green bean fool you. Very little cooking is required to make a green bean completely tender and ready for eating. When placed in a steamer basket and steamed, no more than 3-7 minutes are usually required to obtain the perfect result!

Short term cooking can best retain green beans’ nutrients – focus on vitamin C and vitamin B6

When green beans are cooked for significantly longer periods of time, the loss of nutrients is dramatic. Even one extra minute’s worth of steaming can leech additional vitamins from the green beans! Up to one half of the vitamin C and 40% of the vitamin B6 can be lost when green beans are overcooked.

Effect of cooking on fiber

Much of the stringiness evident in the texture of green beans comes from their high fiber content, notably from their cellulose and hemicellulose content. Luckily, although this fiber content decreases slightly with any amount of steaming, the decrease is not significant. Therefore, by steaming your green beans for a few minutes you can still enjoy the benefit of this important nutrient.

Cover the pot to maximize nutrients

Since some of the nutrients found in green beans are particularly sensitive to light, covering the pot when you are steaming them is another way to reduce nutrient losses while cooking. One of these nutrients is riboflavin (vitamin B2) and studies have shown that prolonged exposure to light is a critical factor in the loss of riboflavin during cooking. Therefore, cover the pot while quickly steaming your green beans so as to help to insure that these vegetables remain a very good source of this very important nutrient.

Cooking and color change

As with most vegetables, color changes that occur in green beans during cooking provide clues about nutrient loss. After 3-4 minutes of steaming, the green beans should start to take on a more vibrant green hue. After 9-10 minutes, you’ll start to notice a drop in the intensity of color. After 15 minutes, you should arrive at a more gray-green shade that is the green bean’s way of confirming major nutrient loss. Our advice: stop when the beans take on their most vibrant shade of green, provided they are still tender enough to enjoy.

Practical tips

To maximize the content of the nutrients of which green beans are concentrated, quickly steam them until they have reached their most vibrant shade of green (3-7 minutes will usually do the trick). Cover the pot or pan whenever possible. Cooking them this way will help you to enjoy green beans that are not only exquisite in color, taste and texture but ones that have also retained much of their nutrient content.


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This page was updated on: 2004-11-22 14:12:00
© 2002 The George Mateljan Foundation