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The change of the osmotic value of different substances was observed during yeast growth by determination of the lowering of freezing-points. In shaken cultures with fermentable sugars the osmotic value at first increased and then decreased (effect of diauxy). Different attenuation degrees of raffinose (1/3, 3/3) as such reflected the osmotic value of the fermented medium. The diminuation of the osmotic value in liquid auxanograms showed distinctly whether the yeast had grown by utilizing the sugar or by using the carbon of amino acids or of reserve substances in the cell itself. By the aid of a calibration curve the ethanol content of a fermented medium may be determined exactly.