If you’ve ever sat down at a pub to a plate of really good fish and chips—the kind in which the fish stays tender and juicy but the crust is supercrisp—odds are that the cook used beer as the main liquid when making the batter. Beer makes such a great base for batter because it simultaneously adds three ingredients—carbon dioxide, foaming agents and alcohol—each of which brings to bear different aspects of physics and chemistry to make the crust light and crisp.

The CO2 escaping from the frying batter makes for a light texture.  This effect is enhanced by the low surface tension, (which in the glass makes the foamy head), keeping the bubbles in place for the duration of the cooking process.  And the alcohol evaporates faster than water so that the crust sets quickly reducing the risk of overcooking.  The story is in Scientific American.