The storage of grape marc: Limiting factor in the quality of the distillate

Grape marc, the mass of skins, stalks and seeds left after the winemaking process, is stored before distillation to produce ethanol by the alcoholic fermentation of the residual sugars. In this work 24 samples of grape marc were stored in four different types of containers. After distillation process, the samples obtained were analyzed by GC–MS to evaluate the influence that the storage exercises on the major volatile composition. Grape marc stored in plastic sacks (1000 kg) produced distillates with low values of the majority volatile compounds, that implies a good quality but a poor aromaticity. Distillates from pomace in plastic drums (250 kg) showed a high content in ethyl esters and higher alcohols, however the concentrations of ethyl acetate and aldehydes and acetal are high too, due to the difficulty to control the aerobic bacteria spoilage. The principal problem of the concrete containers (70,000 kg) is the high methanol production and in the plastic sacks (50 kg) the quick aerobic and anaerobic degradation. With an exhaustive control of oxygen contact, plastic drums and plastic sacks (1000 kg) were the better systems to storage grape marc before distillation.