TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: The fresh material containing matter in fermentation is mixed in a ratio of 1:3 to 1:8, preferably 1:4 to 1:6. For additional injection, the fermenting material is fed into the circuit in a ratio with the fresh waste of 4:1 to 1:1, preferably 3:1 to 2:1. At a maximum, half of the fermenting material is circulated, preferably one-third to one-quarter. The fresh waste has an adjusted pH value of 3-5. The content of the solid matter in the fermenting material for circulation has a concentration of 20-50 wt%, preferably 25-40 wt%. The level of the solid material is adjusted by drying part of the recirculating material to be added to the remainder of the recirculation. The concentration can also be adjusted by the addition of water, sewage, thin sludge or liquid manure, derived from pressing, in the separation of hazardous matter from the fermenting material. The content of ammonia nitrogen in the fermenting material is restricted to a maximum of 4 g/kg. Nutrients can be added for the anaerobic microorganisms. Preferred Apparatus: A recirculation circuit (32) opens into the reaction vessel (1) at a level of 25-70% of the substrate height, and especially 35-50%. Both circuits (2,32) lead from the mixer (6). The dimensions of the reaction vessel (1) give a diameter:height ratio of 1.0:1.3 to 1:4. The collection vessel (5) has one or more conveyor screws (11). The base of the reaction vessel (1) is angled downwards by at least 20degrees towards the conveyor screws (11), in two paths where there are two screws. The conveyor screws (11) lead to an intermediate vessel (13), fitted with barrier slides (12,14). A water extraction station (19), which follows the intermediate vessel (13), has a press action, using added flocking agents. A tank to collect the extracted water from pressing is linked to the mixer station (6), which is also charged from the intermediate vessel (13). Conveyors (31,33,24) link the outlet (30) of the water extraction station (19) with the mixer (6). Direct or indirect heating acts on the material flowing through the common parts of the two circuits (2,32), using a heat exchanger (9) fed with cold water from the motor powered by the biogas delivered from the reaction vessel. EXAMPLE - A reactor with 23m3 of contents was used to ferment 5000kg of organic waste on a weekly basis. The ratio of fresh material to fermentation material of 1:4. In a week, about 1130kg of biogas was produced.