Biomass, sugars and ethanol are the main compounds involved in beverage fermentation processes, although many other minor components, such as esters, also play important roles in the flavour and taste of the final product. These compounds were monitored during cider fermentations carried out on laboratory, semipilot and pilot plant scales (100 ml, 13 and 125 1, respectively) and even during a cider industrial fermentation (45 000 1). the behaviour was similar except for fermentations carried out in Erlenmeyer flasks whose ethanol/sugar yield factor was slightly lower and the ethyl acetate concentration achieved was too high due to the different geometry that gave rise to different metabolic pathways. Simple models are developed to predict the evolution of these compounds during the process and they are successfully applied to simulate experimental results. (C) 2003 Elsevier Science Ltd. All rights reserved.