I remember michael woods tracing the soma plant in NWFP in pakistan and even somewhere else. He found reference to this effect there. It is a herb which when immersed in hot water, developed into a strong concoction that gave energy to the person drinking it. Something similar to redbull.
Soma banam was actually good. Sura banam is the one which can be equated to liquor and this was supposed to be have been consumed by the asuras.