[Problem] To manufacture a foaming member using a low-cost method having little environmental impact, in which the air bubbles in an air-bubble-containing product are enhanced and stability is improved, without imparting viscosity, coloring, flavor, cloudiness, odor, etc. Also, to provide an effective use of yeast cell residue generated as a byproduct of a yeast extract. [Solution] A yeast cell residue remaining after a useful extract is removed from a yeast is suspended in water, and is heated after pH adjustment, and then a supernatant is obtained by centrifugal separation. This fraction contains, in relation to the solid content, 35 wt % or more of protein and 30 wt % or more of dietary fiber, and is usable in the foaming member.
