Model aqueous systems were used for the study of the cooking quality of beans (Phaseolus vulgaris). These systems were created using graded contents of calcium and magnesium ions, in a ratio of 4 : 1, to prepare aqueous media with cation content corresponding to 0Γ400 mg litre~1 of calcium carbonate. The model systems were used to measure the quality of boiled beans in water of low and high divalent cation content. A boiling time of 60 min was used and the hardness of the boiling beans was measured by an Instron Universal Testing Machine. Cooking of beans in water of low divalent cation content equivalent to 0Γ50 mg litre~1 resulted in well-boiled beans for both types (easy-to-CaCO 3 cook and hard-to-cook) of beans. Boiling in water of high divalent cation content led to the formation of very hard beans for both types of bean, while boiling in water of moderate divalent cation content (normal drinking water : 150Γ250 mg litre~1 di β erentiated between the two categories of beans. These results CaCO 3 ) were further tested by adsorption experiments with divalent cations, on beans boiled (a) in di β erent proportions of boiling water, and (b) in model aqueous systems. The divalent cation content of boiling water and the phytic acid content of the beans proved to be the crucial factors in the hard-to-cook phenomenon of beans.