Nowadays, numerous projects are focussed on finding non-polluting energy sources. Interest in the use of biomass for energy purposes has been also revived in this context. Among others, agricultural biomass waste is one of the most promising resources. Its conversion into biofuel for further application via combustion increases its economic interest despite the initial low calorific value. In the present study, the conversion process is carried out in supercritical water (SCW), thus improving significantly the energy balance by eliminating the need for drying the biomass. The SCW dissolution, hydrolysis and oxidation of pure substances in a hydrothermal diamond anvil cell (HDAC) have been studied previously and unique results concerning the homogeneous dissolution of naphthalene, cellulose and glucose were acquired. The current investigation was performed for samples representing real biomass (winery residues) rather than pure substances. Visualizations of the SCW biomass gasification process were obtained and the products of the decomposition were also analyzed. It is expected that this work will contribute in valorizing winery waste by decreasing the cost required for its elimination and will also contribute significantly to green house gases mitigation.