The hydrothermal carbonization is an attractive process to convert biomass of high water content to different products. The requirements on the products, which may be soil improvement material, a substitute for lignite or carbon black, opposites to biomass as feedstock, which has a very complex and variable composition. The goal of this work was to study the influence of an ingredient, here lignin, on the carbonization. In this paper, not only the composition but also the structure is considered.