Abstract: A plant fiber product for use in food products is prepared from straw by cutting and cooking in sodium hydroxide containing liquor, followed by a treatment with ClO.sub.2 in an acid medium, treatment with H.sub.2 O.sub.2 in a basic medium, and again treatment with ClO.sub.2 in an acid medium, said processing steps being carried out for such a period and with such an intensity that substantially all lignin is removed, that the final product is obtained with great whiteness and purity, thereby making the product suitable for the intended purpose.