Which carbonated liquid is sometimes used instead of plain water in tempura batter?

Sparkling water is sometimes used instead of plain water in tempura batter. Its dissolved carbon dioxide forms bubbles that can help create a lighter, airier coating during frying.

The substitution is optional rather than essential. Classic tempura batter relies mainly on cold water, eggs, and soft wheat flour, with the ingredients mixed very briefly. Keeping the batter cold and avoiding overmixing are important because excessive gluten development can make the coating soft and dough-like.

Sparkling water should not be confused with a strongly flavored or sweetened soda. Plain carbonated water is the usual substitute when a recipe calls for it. Some cooks use beer for a related aerating effect, but that changes the flavor and is not the standard answer here.

Tempura’s light texture also depends on technique: ingredients are dipped shortly before frying, and the batter is often prepared in small batches. The result should be thin, crisp, and relatively pale rather than thick and breaded.