Reactions of gases in beer.

Selles, J.F.

Abstract
The behaviour of dissolved gases in beer is reviewed. In aqueous liquids, such as beer, dissolved gas molecules are surrounded and bound by water molecules. Whereas nitrogen remains in its molecular form in solution, oxygen changes its form. At the pH of beer, the formation of hydroxyl ions by the reaction of oxygen with water is limited, so that most of the dissolved oxygen takes the form of single negative ions each surrounded by water molecules with their positively charged ends facing inward (hydrated ions). Both nitrogen and oxygen, held in solution in beer under pressure (as in a bottle or can), move more rapidly than carbon dioxide when they break out of solution on the release of pressure (at dispensing) and thus produce more and smaller foam bubbles, but oxygen engages in chemical reactions which break up the bubble film. Oxygen ions can also be released from hydration by heat, enabling them to react with other beer constituents to form the compounds which give rise to off flavours in overpasteurized beer. The importance of avoiding contact with air in bright beer storage and during packaging is emphasized.
Keywords : air beer nitrogen oxygen quality stability survey