On food and cooking the science and lore of the kitchen ( PDFDrive ) 1411

way the beer is released from keg or can Here are some of the most interesting Grain Proteins Stabilize the Head Foam stability depends on the presence in the bubble walls of emulsifier molecules with water-loving and water-avoiding ends (p 802); the water-avoiding ends project into the gas while the water-loving ends stay in the liquid, and thus reinforce the gas-liquid interface In beer, these molecules are mostly medium-sized proteins that come from the malt or from cereal adjuncts, whose proteins are more intact than malt’s and significantly improve head stability Hop acids also contribute to foam stability, and become concentrated enough in the foam to make it noticeably more bitter than the liquid beneath Cool-fermented lagers generally give more persistent foams than warm-fermented ales because the latter contain more foamdestabilizing higher alcohols from yeast metabolism (p 762) Nitrogen Makes Creamy Foams In the last decade, many beers have come to be endowed with an especially fine, creamy head that used to be largely limited to stouts The creamy head comes from an artificial dose of nitrogen gas that may be injected into beer at the brewery, or in the bar or pub by the tap that delivers beer from the keg, or by a small device inside an individual beer can Nitrogen is less soluble in water than carbon dioxide, so its bubbles are slower to lose gas to the surrounding liquid, and slower to coarsen and deflate Nitrogen bubbles remain small, and persist They also don’t carry the tart prickliness of carbon dioxide, which becomes carbonic acid when it dissolves in beer and on the surface of our tongue Foam in the Glass An initially vigorous pouring action develops the head of foam with a small, easily controlled portion of the beer  ... prickliness of carbon dioxide, which becomes carbonic acid when it dissolves in beer and on the surface of our tongue Foam in the Glass An initially vigorous pouring action develops the head of foam with... is less soluble in water than carbon dioxide, so its bubbles are slower to lose gas to the surrounding liquid, and slower to coarsen and deflate Nitrogen bubbles remain small, and persist They also don’t carry the tart... creamy head comes from an artificial dose of nitrogen gas that may be injected into beer at the brewery, or in the bar or pub by the tap that delivers beer from the keg, or by a small device inside an individual beer can