A method for controlling the isomerization of (-)-epicatechin to (-)-catechin in an epicatechin-containing product, preferably an edible product, which method comprises the step of heating the product at a temperature of up to about 190.degree. C. and at a pH of up to about 8. A method for controlling the isomerization of (+)-catechin to (+)-epicatechin in a catechin-containing product, preferably an edible product, which method comprises the step of heating the product, at a temperature of up to about 190.degree. C. and at a pH of up to about 8. Preferably, the temperature is from about 72.degree. C. to about 125.degree. C., the pH is from about 4 to about 7, and the time is at least about 15 seconds. Under either method, the isomerization may be carried out in an open food processor in a reduced oxygen atmosphere or in a closed food processor. The edible product may be pasteurized, boiled or sterilized during the isomerization. The isomerization is minimized by lowering the heating temperature, by lowering the pH, and/or by lowering the heating time. Conversely, the isomerization is maximized by increasing the heating temperature, by increasing the pH, and/or by increasing the heating time. The edible product may contain or be a fruit product, a vegetable product, a cereal product, a bean product, a nut product, or a spice product.