Grape pomace is the solid residue left after juice extraction from grapes, and represents in Mediterra nean countries the most important by-product of the winemaking industry. Steam distillation of fer mented grape pomace will eventually produce a spirit, designated as bagaceira in Portugal, orujo in Spain and grappa in Italy. This paper comprehensively reviews fundamental and applied aspects of the manufacture of these spirits, encompassing their composition as well as metabolic reactions and microbial ecology that determine such composition during fermentation. These spirits adhere to maxi mum levels of methanol (potential toxic compound) and 2-butanol (potential flavor defect) fixed by EC regulations. Available studies pertaining to bagaceira, orujo and grappa have indicated that the final quality of these spirits depends strongly on the quality of the fresh grapes, the storage condi tions, and the distillation equipment and procedure employed.

The independent and combined effects of the addition of tartaric acid, the addition of pectinases, and the time of fermentation (and the material of the container) on the specific rates of death of lactic acid bacteria and yeasts were experimentally evaluated through a full (or fractional) two-way factorial design for pomace fermentation from the Alvarinho (and the Loureiro) varieties. Microbes present in the pomace prior to fermentation were identified in a preliminary fashion. Knowledge of the behavior of the microflora in grape pomace as a function of each major processing parameter during the step of anaerobic fermentation is important in attempts to eventually standardize and optimize the manufacture of these distilled beverages.