Lupini beans, or lupins, are the seeds of lupinus plants. With origins in the Mediterranean, these high-protein beans are traditionally eaten with beer throughout Southern Europe and Latin America. Due to the bitter taste and high alkaloid content of the beans, special "debittering" methods for lupini beans are common. Although so-called "sweet," low-alkaloid strains are available around the world, some debittering may still be required to remove potentially toxic alkaloids from raw lupini beans.
According to the Australia New Zealand Food Authority, traditional "bitter" lupini beans have much higher concentrations of potentially harmful alkaloids than the "sweet" varieties developed in the 20th century. Because high lupini alkaloid intake is associated with nausea, weakness and visual disturbances, the distinction between the two is important. While bitter varieties have alkaloid concentrations of approximately 500 mg per kg after soaking and cooking, sweet varieties have concentrations of 150 mg per kg or less in their natural state. Although concentrations under 0.35 mg per kg of body weight are not known to cause negative reactions, the recommended maximum daily lupini alkaloid intake for humans is 0.035 mg per kg of body weight.
Failure to properly remove alkaloids from lupini beans can lead to lupini toxicity, Nevada Pingault and colleagues warn in research published in the "Medical Journal of Australia." In a 2009 review of known cases of lupini-related illness, the researchers note that all cases were related to bitter lupin beans that were not properly "debittered." This process, which removes most of the alkaloids from the beans, involves soaking dry beans for a week and changing the water every day. By properly following this soaking process, the Food Safety Network website, run by Canada's University of Guelph, suggests that the beans become edible due to the alkaloids being dissolved and discarded in the water.
Debittering Sweet and Bitter Beans
While the Food Safety Network suggests that bitter beans can be rendered nontoxic through the soaking process, it does not state that cooking is required. Rather than being a required part of the debittering process, cooking the pre-soaked lupini beans is suggested as a means of providing a softer texture. In line with such suggestions for bitter beans, a team headed by Donatella Resta from Italy's University of Milan reported in the journal "Molecular Nutrition & Food Research" that neither cooking nor soaking is required for sweet lupini beans. In their 2008 study of a variety of beans and foods made with lupini, the researchers determined that commercially available, sweet lupini beans are safe to eat without any debittering due to their low alkaloid content.
Is Cooking Required?
Whether sweet or bitter, lupini beans do not have to be cooked for them to be edible. While you might prefer to cook the raw beans to give them a softer texture, raw lupini beans are safe to eat as long as they are properly soaked and debittered. Due to the lack of strict, universal regulation of lupini bean alkaloid content, however, Giovanna Boschin and her colleagues at the University of Milan suggest, in a study published in 2008 in the "Journal of Agricultural and Food Chemistry," that this debittering process be followed for both sweet and bitter varieties to avoid any possibility of lupini toxicity.