The aim of this work was both to model the kinetics of the extraction and transformation of phenolic compounds during fermentation and to propose an index to compare fermentation procedures. Six lots of Sangiovese grapes from five vineyards were used for red wine fermentation tests on lab and industrial scale during 2005 and 2006 vintages. Total phenol index, colour parameters, anthocyanin and pigmented polymer contents were measured during fermentations as variables related to phenolics. Microvinifications performed during vintage 2005 were used to model the evolution of total phenol index at 280 nm, malvidine content, colour parameter a* and pigmented polymer content during fermentation. Vinifications performed during vintage 2006 were used to validate the models. A specific adimensional number, called equivalent index, was set up to specify the operating conditions of red wine fermentation being a function of the extraction and transformation phenomena of phenolic compounds.