Many beans contain a toxic lectin (phytohaemagglutinin), which consists of two-related proteins and which causes sudden food poisoning. Poisoning occurs if the beans are eaten raw, simply soaked, or insufficiently heated. Adequate soaking, followed by heating, completely destroys the lectin.
The highest concentrations of lectin are found in red kidney beans (Phaseolus vulgaris), which is why lectin-induced poisoning is called “red kidney bean” poisoning. The symptoms are most commonly caused as a result of soaked, uncooked beans eaten as they are or in salads. Even a few beans can cause symptoms. The severity of the symptoms is directly proportional to the number of beans eaten. Typical symptoms of food poisoning are nausea, often severe vomiting and diarrhoea. Symptoms begin within 1-3 hours of eating the beans and generally last up to 3-4 hours. No special treatment is usually required, but an adequate fluid balance should be maintained and activated charcoal administered.
Epidemics have been associated with slow-cooked foods as well as with casseroles, where the internal temperature of the food has not risen high enough. Heating food to only +80ºC can even increase toxicity, which even makes it more hazardous to eat such beans than raw beans.
In addition, several beans contain compounds that inhibit the breakdown of proteins in the digestive tract. The effects of these compounds also disappear during cooking.
Broad beans (Vicia faba) are not, despite their name, beans (Phaseolus) but vetches (Vicia). As the properties of broad beans have not been well established, the Finnish Food Authority recommends the same instructions for use as for beans in general.
The effects of the different beans offered for sale vary. However, it is difficult for the consumer to know the individual characteristics of each bean species. This is why it is always a good idea to cook fresh beans before use, for example by boiling. When using dried beans, the following general instructions should always be followed:
- soak all beans overnight (for a minimum of 12 hours) and rinse; and
- boil for at least half an hour or longer if necessary. After this, the beans can be safely eaten in salads, soups, casseroles and other foods.
Soaking the beans is an important step, as it reduces the cooking time of the beans, while keeping it reasonable, and giving a steadier and safer result than without soaking.
Under Article 9 of Regulation (EU) No 1169/2011 of the European Parliament and of the Council (the Food Information Regulation), the packaging shall, where appropriate, include instructions for use, such as a warning to inform and protect the consumer.
In view of the above, the Finnish Food Authority considers that the packaging of dried beans and broad beans must bear the following warning and instructions for use:
- “Beans may not be eaten unprocessed. They must be soaked overnight, rinsed and cooked for at least… time (Bean-specific cooking times.)
The name of the bean must also be indicated on the bean package. The generic name “beans” alone is not sufficient.