Yeast affects several aspects of beer including the foam, or head, that forms on the of the glass. If fermentation is too vigorous, too many of the foam-stabilizing proteins may be lost. Cate Gillon/Getty Images hide caption

itoggle caption Cate Gillon/Getty Images

Twins in Malawi helped scientists discover a role the gut microbiome appears to play in severe malnutrition. Photograph courtesy of Tanya Yatsunenko hide caption

itoggle caption Photograph courtesy of Tanya Yatsunenko