A method of gasification using a downdraft gasifier having a plurality of vertically positioned tubes to create a pyrolysis zone, an oxidation zone beneath the pyrolysis zone and a reduction zone beneath the oxidation zone. The shape of the tubes eliminates the need for a restriction (hearth) in the gasifier, which limits the maximum achievable throughput. A rotating and vertically adjustable grate is located beneath, but not attached to, the reduction zone of the gasifier.