The Fate of Copper and Iron During Fermentation of Grape Musts

¹ Department of Viticulture and Enology, University of California, Davis

(1) Identical fermentations were carried out with various concentrations of copper and iron present in the fermenting medium.

(2) The removal of copper during fermentation ranged from 40.9 to 89.0 per cent, whereas that of iron ranged from 47.5 fo 70.0 per cent.

(3) Of the removed copper, a total of 0.1 to 2.5 mg of copper was found in the yeast washings, whereas 0.97 to 12.2 mg of copper per gm of dried yeast was found in the yeast cells.

(4) The removed iron is dispersed as follows: 0.03 to 1.6 (total) mg of iron is found in yeast-washings and 0.47 to 24.2 mg of iron per gm of dried yeast in or on the yeast cells.

(5) From our experimental data we conclude that metallic ions are incorporated by the yeast, for the most part, during alcoholic fermentation.

(6) pH tends to decrease when high concentrations of metals are present during fermentation.

(7) High copper or iron concentrations in fermenting media cause the yeast cells to appear darker.