Batter frying: tempura and beer batter

Why

Flour and water form gluten (see the Kneading and gluten card), and the longer the batter is mixed or left standing, the tougher, denser and gummier the coating; ice-cold water slows gluten formation, while alcohol (vodka) and corn or rice starch in place of part of the flour limit it, so tempura is mixed only briefly and small lumps stay in it. Bubbles from sparkling water, beer or baking powder expand in the hot oil and puff the coating into a thin, delicate crust; according to America's Test Kitchen, the acidity of sparkling water also holds back gluten formation. In oil heated to about 170–180 °C the water in the batter turns rapidly to steam, the coating sets quickly and absorbs little fat, whereas in lukewarm oil or an overcrowded pan it stays soft and greasy (see the Deep-frying in oil card). Batter holds only on a dry surface: steam escapes from wet fish or vegetables during frying and the coating slides off, and a thin layer of flour or starch under the batter helps it cling.

How to do it

• Pat fish, prawns or vegetables dry, cut them into even pieces, salt them and dust lightly with flour or starch; shake off the excess.
• Mix the dry ingredients in advance, but stir tempura together with ice-cold sparkling water only just before frying; a beer batter with some starch can rest briefly in the fridge.
• Stir tempura with chopsticks or a fork for only a few seconds and leave the lumps; whisk beer batter until smooth and then stop.
• Heat the oil to about 170–180 °C as the recipe says and check it with a thermometer; let pieces drip off excess batter and add them in small batches, carefully and away from you.
• Fry potatoes and sweet potatoes in batter at no more than 175 °C and only until golden, not brown.
• Drain the fried pieces on a rack and serve as soon as possible; covered or stacked on top of each other they go soft.

If it goes wrong

A soft, greasy coating was fried in lukewarm oil or an overcrowded pan: let the oil heat up again and make the next batch smaller; absorbed fat cannot be removed. Dense, gummy batter was overmixed or stood too long, so mix a fresh cold batch. A coating that falls off will hold next time if you dry the food and dust it with flour or starch. Return pieces that have gone soft to hot oil for 1–2 minutes or to a hot oven for a few minutes.