Green Bean Seed Identification: And Why Raw Kidney Beans Are Dangerous

The kidney bean warning

Red kidney beans contain the highest levels of phytohaemagglutinin of any common bean. It is destroyed by boiling, but only by boiling. Slow cooking at a low temperature, which is how most people  cook a casserole, does not destroy it and can actually concentrate it as the water evaporates.

The safe method is this: soak the beans overnight, drain them, cover with fresh water and boil hard for at least ten minutes. After that you can simmer them as long as you like. A slow cooker on its own is genuinely dangerous for kidney beans unless they have been boiled first.

White kidney beans, cannellini, contain the toxin at lower levels but the same rule applies. This is why canned beans are safe: they have already been boiled.

Snap beans, shelling beans and drying beans

Identifying beans from the seed

• Red kidney. Large, dark red, distinctly kidney-shaped with a white hilum scar. The one to be careful with.
• Cannellini and white kidney. Large, white, kidney-shaped. Same shape as red kidney, different colour.
• Borlotti and cranberry. Cream with red or maroon speckles and streaks. Very distinctive.
• Black bean. Small, black, oval and glossy. Almost no markings.
• Navy and haricot. Small, white, oval. The classic baked bean.
• Pinto. Medium, beige with brown streaks, looking mottled or painted.
• Flageolet. Small, pale green, kidney-shaped. Immature when sold.
• Green bean and French bean seed. Small, kidney-shaped, usually pale brown or white when dried, and grown for the pod rather than the seed.
• Broad bean. Very large, flat, pale green or brown, with a thick leathery seed coat.
• Peas. Round, smooth, yellow or green, with no kidney shape at all. The roundness is the giveaway.

Identifying beans from the pod

If you have the pod, the identification gets much easier. Green beans, French beans and wax beans have thin, fleshy, stringless pods eaten whole. Runner beans have longer, flatter, rougher pods that are usually stringed before cooking.

Borlotti and cranberry beans have striking pods, cream with bright red or magenta streaks, and they are grown as much for their looks as for the beans.

Broad beans have thick, fat, slightly fuzzy pods with a pronounced velvety lining, and the beans inside are huge.

If the pod has dried on the plant and gone papery and brown, you have a drying bean, and you are looking at the seed harvest rather than a fresh vegetable.

Growing them

• Climbing beans need a support two metres tall and  produce over a longer season than bush types.
• Bush beans need no support and crop all at once, which suits a single harvest or a freezer batch.
• Pick snap beans young and often. The more you pick, the more the plant produces, and beans left to mature stop flowering.
• For drying beans, leave the pods on the plant until they rattle, then shell and dry them fully before storing.
• Save seed from open-pollinated varieties, not hybrids, if you want it to come true next year.
• Beans fix nitrogen, so they are a good crop to follow with something hungry like leafy greens.

This is the page where I have to start with a warning rather than a story. Raw and undercooked red kidney beans contain phytohaemagglutinin, and a handful of them is enough to make a healthy adult seriously ill within a few hours.

The reason it matters here is that dried beans are sold loose, unlabelled, from bins and from friends who grew too many. If you cannot identify the bean, you cannot know how carefully it needs cooking.

So this page does two jobs: identify the bean, and tell you how it has to be cooked.