A superacidic ester group is useful in the production of ionomers for polymer electrolyte fuel cells. A spring is supported on the counterholder and is intended for prestressing a closing part against a valve seat. The coarse oat flour is first dry classified to separate or form a coarser fraction oat bran containing more concentrated \u03b2-glucan and a finer oat flour or starch containing or endosperm containing fraction.