Cooked must is the starting raw material used to produce Aceto Balsamico Tradizionale (ABT). It is obtained from grape musts that are condensed by a gentle simmering in uncovered pans over an open fire. Concentrations of fructose, glucose, furfural and 5-Hydroxymethylfurfural (HMF) during must preparation were evaluated as quality indicator of the final product. High pressure liquid chromatography (HPLC) technique was used for the determination of the analytes content in cooked musts sampled at different time during their preparation. Two varieties of grapes (Trebbiano Montanaro and Salamino), and different cooking apparatus were tested by using vats with different surface/volume ratio. The concentrations of the analytical species were found to be dependent on both the kind of grape and the cooking technology. Sugars concentration increases during cooking following almost a linear trend; on the contrary, furfural compounds, produced by monosaccharides degradation, significantly increase with an exponential trend only in the final step of the process. The analytical method gives good recovery values for all the investigated species, ranging from 91% to 104 %. (c) 2006 Elsevier Ltd. All rights reserved.