Nitrogen is an element most often found in beer in its gaseous form (N2) or as a constituent of larger molecules, such as proteins, amino acids, and nucleotides.
In its gaseous state, nitrogen is important to brewers as a plentiful and inert gas (N2 makes up 78% of the atmosphere). N2 is often used to purge vessels or packages of unwanted oxygen in applications varying from purging a brew kettle to avoid hot-side aeration to purging packages of hops for storage. Also, N2 is used as an ingredient in nitrogenated beers, where it adds no flavor but produces very fine, stable bubbles (in comparison to N2, carbon dioxide produces relatively large bubbles with a tart, acidic flavor).
N2 in its liquid state (LN2), which at atmospheric pressure is between –195.8°C and –210°C (–320.8°F and –410°F), can be useful to brewers as a refrigerant for the cryogenic storage of yeast cells. Also, LN2 can be dripped into bottles or cans before they are filled with beer. In this application, the LN2 rapidly evaporates upon hitting the bottom of the package and subsequently purges the package of unwanted air.
In bars and restaurants, nitrogen is often part of a gas blend (with CO2) used to drive draught systems. At normal draught system operating pressures, nitrogen is far less soluble in beer than CO2 and therefore can be used to help push beer to the tap without concern about dissolution of nitrogen into the beer. The proper ratio of nitrogen to CO2 will depend on temperature, pressure, and the desired carbonation level of the beer. It is worth noting that nitrogen pressure will not hold CO2 in beer. Many draught systems that run on a gas blend containing 75% nitrogen, a blend meant for the dispense of Irish stout, will end up serving flat beer as a result.