NOVELTY - The method comprises fermenting microorganism in a tray comprising a solid state fermentation substrate. The tray has a top surface and cylindrical depressions provided on the top surface. Each depression comprises the fermentation substrate. The tray further comprises two side walls extending upward from a length of the top surface and two rear walls extending upward from a breadth of the top surface, and/or a lid for covering the top surface of the tray. A height of side wall is less than a height of rear wall.    USE - The method is useful for solid state fermentation of a microorganism producing an end product such as a metabolite such as enzyme or a microorganism including a fungus or a bacterium (all claimed), where enzyme includes amylases, proteases, lipases, pectinases, tannases, arabinases, xylanases, and cellulases, the microorganism further include actinomycete, yeast and alga, the fungus include e.g. Aspergillus, Trichoderma, Rhizopus, Cerenna, Coriolus, Pleurotus, Lentinula and Gliocladium and the bacteria include Pseudomonas, Bacillus, Vibrio, Aeromonas, Staphylococcus, Chryseobacterium and Citrobacter, and the end product further includes: rennet; pigments; aromas and flavor compounds; small organics including ethanol, oxalic acid, citric acid and lactic acid; plant growth hormones including gibberellic acid; protein-enriched agricultural residues used as animal feeds with reduced levels of toxins or with improved digestibility; antibiotics including penicillin and oxytetracycline; biological control agents including bio-insecticides and bioherbicides; and spore inocula including spore inoculum of Penicillium roqueforti for blue cheese production.    ADVANTAGE - The method is capable of easily fermenting the microorganism with increased yield.    DETAILED DESCRIPTION - The method comprises fermenting microorganism in a tray comprising a solid state fermentation substrate. The tray has a top surface and cylindrical depressions provided on the top surface. Each depression comprises the fermentation substrate. The tray further comprises two side walls extending upward from a length of the top surface and two rear walls extending upward from a breadth of the top surface, and/or a lid for covering the top surface of the tray. A height of side wall is less than a height of rear wall. The rear walls and side walls are joined at corners along their height of the top surface of the tray. A yield of an end product is increased by 20% compared to a fermentation done using a flat tray without depressions. The depressions are equally spaced on the top surface of the tray. A depth of the depression is 1-10 cm, and/or a length of the depression at its widest point is 5-15 cm. A volume of the depression is 40-400 cm3. The depressions at the extreme end along the length of the top surface are 1-5 cm from the extreme end of the top surface. A distance between two successive depressions along the length and breadth of the top surface is 0.5-5 cm.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic top view of a tray bioreactor.