Beer batter is a liquid batter made from flour and beer, used to coat food before deep-frying or pan-frying it to a light, crisp, golden crust.
The beer's carbonation and alcohol content produce an airy, crunchy texture as the food fries, and it adds a subtle, slightly yeasty flavor. The technique is most associated with British pub fare, especially fish and chips, though it's since spread to onion rings, calamari, chicken, and other fried foods.
Lighter, more carbonated beers like lagers and ales are typical; darker beers such as stouts add a richer, more complex flavor. Food is usually fried around 350-375°F until golden and crisp.