Differential scanning calorimetry (DSC) was used to describe compost organic matter quality with regard to input materials and humification. Several basic experiments using 10 selected compost samples were performed to find out how material composition and humification affect the heat flow of the sample and the shift of the second exothermic organic peak. Each input material contributes to the specific DSC profile of the whole compost sample. Biowaste composts from the separate collection can be distinguished from sewage sludge composts due to the specific thermal pattern. Despite the influence of the material itself on the thermal behavior, chemical changes of the progressing process effect the heat flow. Humification of biogenic waste materials causes increasing intensities of the second exothermic peak. Principal component analysis (PCA) was applied to reveal the inherent features in the DSC profiles of 24 compost samples (final products). Thermal characteristics enable the assignment of different materials (sewage sludge and biowaste) to their compost class according to the intended use. Based on these specific thermal features quality assessment of compost organic matter can be performed very fast. DSC profiles of humic acids extracted from the 10 selected composts were recorded. Although similarities of the thermal behavior are visible, each DSC profile shows individual properties with regard to peak position and intensity. Different carbon and nitrogen contents confirm the particular composition of compost humic acids. (c) 2007 Elsevier B.V. All rights reserved.