After seven years of research, scientists have uncovered what many consider the holy grail of brewing: the underlying formula that determines why some beers keep a thick, lasting head of foam while others collapse almost instantly. Credit: Shutterstock For many people, a glass of beer feels incomplete without a thick, creamy layer of foam resting on top. Yet anyone who enjoys beer knows that this foam often disappears quickly, collapsing before the first sip. Some varieties, however, manage to