Finger-length pods dangle among vines that have wound their way to the top of the trellis. Your hand pauses. Pick them now and blanch them for dinner, or leave them until the beans fill out? People who find pole beans through a search engine land at this same spot with the same question. "It's a bean, so why does everyone say it has almost no protein?" The answer depends on the day you pick.
Two Foods From One Plant
Pole beans are the climbing varieties of the common bean (Phaseolus vulgaris). Eat the young pods whole, before the seeds mature, and they are called green beans or snap beans. Let the pods dry on the vine and shell out only the seeds inside, and they are called kidney beans. The same plant sells under two names depending on nothing but the day it was picked. China, Indonesia, India, Türkiye, and France are the biggest growers, and in every one of those countries the pods go to the produce stand while the seeds go to the grain merchant. The pole bean entry in the Homiclub crop guide lists both uses side by side.
100 Grams of Pods, 100 Grams of Seeds
Set the two side by side using figures from the U.S. Department of Agriculture's FoodData Central and the answer comes into view. Both values are per 100 g, boiled and drained.
- Young pods: 35 calories, 1.9 g protein, 3.2 g dietary fiber, around 10 mg vitamin C
- Mature seeds: 127 calories, 8.7 g protein, 6.4 g dietary fiber, almost no vitamin C
That is more than four times the protein and more than three times the calories. Nutritionally, a pole bean eaten as a pod sits closer to leafy greens than to grains. Let the seeds mature, though, and you get the same protein as the boiled kidney beans you would spoon into a soup or salad. "It's a bean with no protein" is true only while you are eating the pods, and stops being true the moment you harvest the seeds. The figures here describe nutrient composition. They are not a claim that the bean prevents or treats any disease.
What the Pod Offers: Fiber and Vitamin K
The crisp snap you get when you bite into a pod comes from insoluble fiber. It does not dissolve in water, so it travels to the gut intact and adds bulk to stool. Pods also carry vitamin K, which is fat-soluble. Because it dissolves in fat, sautéing the beans in oil with garlic, or blanching them and tossing them in toasted sesame oil, helps the body absorb it. One caution. People taking anticoagulants such as warfarin are often told to keep their vitamin K intake steady from day to day. Suddenly starting on a plateful every evening just because the harvest is in is best avoided. Once the seeds swell and the pod bulges, a tough string forms along the seam, and no amount of blanching will soften it. That is why pods meant for the table have to be picked before that point.
How to Choose the Day
So which day is it? In the Northern Hemisphere, pole beans sown in April or May set pods from July through September. For pods you plan to eat as a vegetable, pick them at 10 to 15 cm (4 to 6 inches) long, before the seeds inside show through the skin. Harvest every two or three days and the vine keeps flowering, giving you several weeks of picking from a single plant. For seeds, leave a few pods on the vine and do not touch them. Harvest when the pods have dried yellow and rattle when shaken, then shell the beans and let them dry another week or so somewhere with good airflow. A plant carrying mature pods sets fewer new flowers, so if you designate some plants for pods and others for seeds from the start, you get both.
Seeds come with stricter cooking rules than pods. Beans in the kidney bean family carry a lectin called phytohaemagglutinin, and the seeds hold far more of it than the pods do. The 2012 edition of the Bad Bug Book, the U.S. Food and Drug Administration's guide to foodborne illness, notes that as few as four or five raw beans can bring on stomach pain and vomiting. Follow that guide's method. Soak the beans in water for at least five hours, discard the soaking water, boil them hard in fresh water for at least 10 minutes, then turn the heat down and simmer until fully tender. Avoid long, low cooking at around 80 °C (176 °F), which leaves the lectin intact.
A pod picked this week becomes a vegetable that gives you fiber and vitamin K. The same pod left six more weeks becomes a bean that gives you protein. For anyone who arrived here after typing "pole bean protein" into a search bar, the answer is less a number than a date. Which nutrition ends up on your table is settled the day you reach out your hand at the trellis.
