Kjeldahl method requires to convert organic nitrogen into its inorganic form. This is achieved by boiling the substrate in sulfuric acid and the process is called digestion. Compact block digestion systems for simultaneous multiple Kjeldahl digestions of up to 40 samples are offered. These systems are equipped with precise temperature control that permits the conditions for the digestions to be optimized thus providing reproducible results. Temperature controller may be provided in a separate block to further increase the convenience of use.