Bose-Einstein condensation (BEC) is a purely quantum phenomenon whereby a macroscopic number of identical atoms occupy the same single-particle state(1), Interest in this phenomenon has grown considerably following the direct demonstration of BEC in low-density gases of alkali metal atoms(2-4). It is therefore worth reconsidering the case of liquid He-4, which is generally accepted to have such a condensate(5), but for which similarly direct evidence is lacking(6). Nevertheless, theoretical models that depend on the existence of a condensate have proved successful at explaining many of the properties of this system(7-9), and BEC is considered to underlie the striking phenomena of superfluidity and quantized vorticity observed in liquid He-4. So the current issue is not whether there is a condensate in this system, but how to demonstrate its existence in a clear and simple way. Here I argue that an earlier measurement(10) of evaporation from liquid He-4 caused by a collimated beam of phonons provides such a demonstration. The calculated angular distribution of evaporated atoms agrees well with that measured if it is assumed that the atoms initially had zero momentum parallel to the surface of the liquid-this is to be expected if the atoms originate from a condensate. This process of quantum evaporation also opens the possibility for creating beams of phase-coherent atoms of short wavelength.