Influence of Must Processing on Iron and Copper Contents of Experimental Wines

¹ United Vintners, Inc., Asti, California.

Grape musts of four varieties were dejuiced and the drained musts pressed to yield a series of juices for each grape lot. Both original and clarified juices were fermented into wines and the latter analyzed for iron and copper. Juices high (10-38%) in suspended solids yielded wines that were generally high (10-20 ppm) in iron and low (0.1-0.2 ppm) in copper. Wines from juices lower in suspended solids and from centrifuged juices were lower (2-5 ppm) in iron and higher (0.2-0.7 ppm) in copper. The load-to-load variability in grapes caused large differences in the wine analyses. If juices were clarified promptly, the method of dejuicing and the severity of pomace-pressing had little influence on the iron and copper contents of the wines. During fermentation, iron passed from the suspended solids into the wine. The suspended solids are believed to constitute a source of sulfur that yeasts reduce to sulfide, which, in turn, precipitates copper as copper sulfide. The removal of suspended solids from juice thus contributes to improved wine quality in several ways.