The present invention relates to a method for treating carbohydrate- containing vegetable material with acid, comprising the steps of: (a) providing a mixture of a carbohydrate-containing vegetable material, an organic acid and, if necessary, water, (b) heating the mixture obtained in step (a) to a temperature of at least 120 °C for some time so as to obtain a mixture comprising an acid-treated insoluble vegetable material, water, a carbohydrate-containing vegetable material that has been rendered soluble and possibly an organic acid, (c) repeating step (b) at least once, with steps (d) and (e) being carried out prior to step (b): (d) separating the acid-treated insoluble vegetable material from the mixture obtained in step (b) so as to obtain a liquid fraction which comprises carbohydrate-containing vegetable material that has been rendered soluble, (e) adding additional carbohydrate-containing vegetable material and possibly additional organic acid to the liquid fraction obtained in step (d), wherein the mixture that is used upon repeating step (b) is the mixture that is obtained in step (e).
