Beans, peas, and legumes that are more than a couple of months old or are of inferior quality always require soaking before cooking. It was once thought that these dried products required a presoaking of at least eight hours, but it is now felt that a three-hour soaking period is sufficient to soften them for cooking; a longer period allows the lime and iron content of the soaking water to harden the outer casing of the product, which would require even longer cooking. Prolonged soaking can also cause fermentation to begin. Most beans, peas, and legumes can be tenderized for cooking by covering them with cold water, bringing them to a quick boil, and then draining. Split peas do not require soaking prior to cooking.