The Science of Perfect Tempura

Because you deserve the crispiness 

You're adventuring through the back alleys of Tokyo, and you come upon a restaurant. You have no idea what it serves, whether if it's good or not, but you're hungry and just want a quick bite to eat. As you enter the chef greets you energetically, 

'いらっしゃい！こちらへどうぞ。’

You don't understand him but from his hand gesture you assume he wants you to sit at the counter seat. Luckicly enough he offeres you an English menu and you quickly scan through it, trying to look like you know what you're doing. There are a lot of unfamilair menus, but you happen to come upon something that you can recognize. Tempura.

As you patiently wait for your meal, the chef makes a fresh batch of batter and starts to fry each vegetable with presision. Sweet potato, asparagus, shrimp, that green leafy thing that looks like parsley but probably isn't. Tsssssssss. Finally the dish is presented to you.

The perfect crunch. You are in heaven.

It's hard for anyone who has tried good tempura to forget that satisfying crunch and lightly fried batter. You try to re-create at home, watching all the Youtube videos and reading the best online recipes filled with all the dos and don'ts of tempura. You finally end up with your first batch of deep fried heaven, and are utterly disappointed. 

While making the perfect tempura batter with only water, flour, and eggs is possible, most likely you'll need a lot of practice and precaution or you'll end up with a soggy, greasy, chewy abomonation. SImply put, making good tempura isn't easy. But luckily with science on our side, we have a pretty good chance. 

The biggest reason why tempura ends up greasy and chewy is mainly because of two things: Gluten and Boiling Temperature. So how can we eliminate these two factors from the batter?

Fig. 1 - Magnified image of gluten structure when water was added to flour without any mixing.

Fig. 2 - Magnified image of gluten structure after water was added to flour and kneaded for a few seconds. 

First, gluten does not exist in nature, it is formed only when wheat flour and water is mixed. The glutenin and gliadin in wheat loosens up and tangles up with each other was mixed with water. Gluten is a stretchy structured protein that is a great thing when making bread, but not when trying to make the greatest tempura in the world...tribute. What's worse is that the gluten structure also holds on to water and fat, which would make a pretty bad piece of tempura.

Glutenin and Gliadin tangle up together to form gluten.

Next, the boiling temperature of the water mixed into the batter naturally has a boiling point of 100°C, letting the water to evaporate and crisp up. What's wrong with this you might ask. Well 100°C is an awful high boiling point compared to, let's say, alcohol which has a boiling point of 78.4°C. Lower boiling point means faster evaporation of liquid, and means the batter spends less time in oil. Also, as I mentioned before, gluten is generated when wheat flour is mixed with water. Alcohol, although a liquid, is not water. So the batter will, mix but form less gluten than a water-based mixture. It is also possible to prohibit the form of gluten by using rice flour, that does not contain glutenin or gliadin.

So the next time you try to make great tempura batter, ditch the old H2O and switch it up with some distilled potates. The results will surprise you.