Kidney beans, also known as red beans, are a variety of the common bean (Phaseolus vulgaris). They are named for their visual resemblance in shape and color to a human kidney. Kidney beans are commonly used in chili con carne and are an integral part of several cuisines around the world. However, raw or undercooked kidney beans contain a toxin called phytohaemagglutinin that can cause severe gastrointestinal distress. Proper preparation is necessary to destroy the toxin and make kidney beans safe to eat. This article will provide an overview of kidney beans, explain why they must be cooked properly, and detail methods for making them safe to consume.
Background on Kidney Beans
Kidney beans have been cultivated for thousands of years in Central and South America. Today, they are grown in many countries around the world, with major production in India, Brazil, Myanmar, and the United States. There are many varieties of kidney beans, including light and dark red, pink, white, black, spotted, and mottled. They are used interchangeably in recipes.
Nutritionally, kidney beans are an excellent source of protein, fiber, iron, and several vitamins and minerals. One cup of cooked kidney beans contains approximately:
- 225 calories
- 15 grams protein
- 13 grams fiber
- 80% RDA for folate
- 25% RDA for iron
- 15% RDA for potassium
In addition to their nutritional value, kidney beans have a meaty texture and absorb flavors well, making them a versatile ingredient in many dishes. Their major uses include:
- Chili con carne
- Red beans and rice
- Three bean salad
- Vegetarian tacos, burritos, and burgers
- Soups and stews
However, raw or improperly cooked kidney beans contain a natural toxin that must be destroyed by thorough cooking.
Understanding Phytohaemagglutinin
Kidney beans contain relatively high amounts of a lectin called phytohaemagglutinin. Lectins are carbohydrate-binding proteins that are widespread in the plant kingdom. However, the lectin found in raw kidney beans, called phytohaemagglutinin or PHA, is toxic to humans. PHA binds to receptors on red blood cell membranes, causing the cells to clump together or agglutinate. This disrupts circulation and deprives tissues of oxygen, resulting in sickness and potential death in high enough doses.
PHA is not denatured by stomach acid and is resistant to breakdown in the digestive tract. The lectin remains biologically active, passing into the bloodstream and causing symptoms of food poisoning, which can appear rapidly within 1-3 hours after consumption. PHA toxicity primarily affects the gastrointestinal tract, causing nausea, vomiting, diarrhea and abdominal pain. Severe cases can lead to disruption of blood circulation, weakness, kidney failure, or death.
The good news is that proper cooking easily destroys the lectin, making kidney beans perfectly safe to eat. Still, consuming even a small handful of raw or undercooked beans can bring on symptoms, so correct preparation is essential.
Methods for Cooking Kidney Beans Safely
Kidney beans must reach a minimum internal temperature of 175°F (80°C) under moist heat conditions to destroy the toxic lectin PHA. This can be achieved through several cooking methods:
Boiling
Boiling kidney beans in water is a safe and effective method to prepare them from their raw or dried state:
- Rinse and sort through raw beans, removing any pebbles or damaged beans.
- Place in a pot, cover with at least 3 inches of cold water and bring to a boil.
- Boil vigorously for at least 10 minutes with the lid on.
- Check beans for doneness. They should be tender but still hold their shape.
- Drain and use beans as desired.
Boiling for 30 minutes is recommended to ensure kidney beans are fully cooked through. The beans will triple in size as they rehydrate. Discard any beans that appear discolored or shriveled after cooking.
Slow Cooker
Using a slow cooker is another hands-off approach to prepare kidney beans:
- Rinse raw beans and add to slow cooker insert.
- Fill with water 2-3 inches above beans.
- Cook on HIGH heat for 3-4 hours until beans are tender.
- Drain and use as desired.
Make sure beans reach a sustained boil in the slow cooker to eliminate PHA. Do not cook on lower heat settings.
Pressure Cooking
Pressure cooking is a fast, convenient method to prepare beans:
- Rinse raw beans and add to pressure cooker.
- Cover with 2 cups water or broth.
- Lock lid and bring to high pressure.
- Cook for 25-30 minutes at high pressure.
- Use natural release method before opening lid.
- Drain and use beans as desired.
The intense heat and pressure of pressure cookers allow kidney beans to become fully tender and safe in much less time.
Canned Beans
Canned kidney beans have already been cooked, making them safe to eat straight from the can:
- Look for BPA-free cans when possible.
- Drain and rinse before using to reduce sodium.
- Use within shelf life; discard bulging, dented or leaking cans.
Avoid recipes that call for adding raw kidney beans to dishes cooked below 175°F, like casseroles or slow cooker meals. The beans must be boiled first on the stovetop before integrating into such recipes.
Are Kidney Beans Ever Safe to Eat Raw?
It is unsafe to consume raw or undercooked kidney beans or use in recipes uncooked. Sprouting or fermenting beans does not eliminate the toxic lectin. Even canned beans should always be cooked thoroughly again before eating.
However, some exceptions when kidney beans may be eaten raw include:
- Commercially prepared bean salads or tabouli that contain vinegar. The acidity helps break down PHA over time.
- Canned beans that will be immediately pureed into spreads like hummus. Mechanical processing helps destroy lectins.
In these cases, only small serving sizes should be consumed, and individuals with sensitivity should take extra precautions.
Tips for Cooking and Storing Kidney Beans
Follow these additional recommendations for safely working with and preparing kidney beans:
- Sort through raw beans and discard any stones, debris or shriveled beans before cooking.
- Rinse thoroughly to remove dirt and excess lectins on the surface.
- Use separate cooking utensils and cuttings boards to handle raw beans.
- Soak beans overnight in water to reduce cooking times.
- Add salt, acids or baking soda only after beans are cooked through.
- Refrigerate cooked beans in a covered container for up to 5 days.
- Freeze beans for longer storage; thaw before using.
- Bring stored beans back to a boil before eating.
Properly cooked kidney beans are a nutritious addition to salads, rice dishes, soups and stews. Take the necessary precautions when preparing them to avoid lectin toxicity. With the proper techniques, kidney beans can be a tasty and healthy plant-based protein source.
Conclusion
Kidney beans are a popular legume rich in protein, fiber and nutrients. However, raw or undercooked kidney beans contain a toxic lectin called phytohaemagglutinin that can cause severe gastrointestinal distress. To safely consume kidney beans, they must be boiled for at least 10 minutes to destroy the lectin. Other safe cooking methods include pressure cooking, slow cooking and preparing canned beans. While some exceptions exist, kidney beans should always be thoroughly cooked before eating to avoid toxic effects. Following proper handling and cooking techniques allows the nutritional and culinary benefits of kidney beans to be safely enjoyed.