Biogas stoves are made in two parts: the burner itself, which mixes gas and air and feeds it to the flame ports, where it burns; and the frame within which it sits, which uses the flame to heat cooking pots or to generate light or use the heat in some other way. The frame for a stove supports the burner on legs and holds cooking pots the right distance away from the flame for effective heating. See the images below, look out for the frame (in red) and the burner.
The amount of gas that flows into the burner is controlled by the jet, a hole which is carefully sized. The air and biogas are mixed and fed to a ‘manifold’ which feeds the flame ports, where it burns. The burner ports are drilled into a shaped cap, which can be removed for cleaning if food is spilled into the burner ports.