Specially formulated tempura flour is available in Japanese supermarkets. This is generally light (low-gluten) flour and occasionally contains leaveners such as baking powder.
Some varieties of tempura are dipped in a final coating, such as sesame seeds, before frying. Tempura generally does not use breadcrumbs in the coating. Generally fried foods which are dipped in breadcrumbs (panko) are considered to be furai (Japanese-invented faux western-style deep fried foods, such as tonkatsu or ebi Fried Prawn).
Thin slices or strips of vegetables or seafood are dipped in flour, then the batter, then briefly deep-fried in hot oil. Vegetable oil or canola oil are most common, however tempura was traditionally cooked using sesame oil. Many specialty shops still use sesame oil or tea seed oil, and it is thought that certain compounds in these oils help to produce light, crisp batter.
When cooking shellfish, squid, or hard-skinned watery vegetables such as bell pepper or eggplant, it is important to score the skin with a knife to prevent the ingredients from bursting during cooking. Failing to do so can lead to serious burns from splashing oil.
Oil temperature is generally between 160 and 180 degrees Celsius, depending on the ingredient. In order to preserve the natural flavour and texture of the ingredients, it is important not to overcook tempura. Cooking times range between a few seconds for delicate leaf vegetables, to several minutes for thick items or large kaki-age fritters.
It is important to scoop out the bits of batter (known as tenkasu) between batches of tempura, so they do not burn and leave a bad flavour in the oil. A small mesh scoop is used for this purpose. Tenkasu are often reserved as ingredients in other dishes or as a topping.
Common ingredients in traditional tempura include:
Nearly any food may be used so long as it does not release water into the batter before or during frying. Rice and other cereals, processed foods such as tofu, and watery foods such as cabbage and fruit are generally not used, although some versions of agedashi dofu resemble tempura.
Tempura is also used in combination with other foods. When served over soba (buckwheat noodles), it is called tempura soba or tensoba. Tempura is also served as a donburi dish where tempura shrimp and vegetables are served over steamed rice in a bowl (tendon) and on top of udon soup (Tempura Udon).
Tempura was introduced to Japan in the mid-sixteenth century by early Portuguese and Spanish missionaries and traders. The word tempura may be derived from the Portuguese noun tempero, meaning a condiment or seasoning, or from the verb temperar, meaning "to season." There is still today a dish in Portugal very similar to tempura called peixinhos da horta, "garden fishies." However, the Japanese language could easily have assumed the word "tempero" as is, without changing any vowels. A far more likely explanation for the word is that it is derived from "tempora," a Latin word meaning "times", "time period" used by either Spanish or Portuguese missionaries to refer to the Lenten period (ad tempora quadragesimae), Fridays, and other holy days when they could not eat meat.
It is thought that as the term "tempura" gained popularity in southern Japan, it became widely used to refer to any sort of food prepared using hot oil, including some already existing Japanese foods. Today, the word "tempura" is also commonly used to refer to satsuma age, a fried fish cake which is made without batter.
In Japan, restaurants specializing in tempura are called tenpura-ya and range from inexpensive fast food chains to very expensive five-star restaurants. Many restaurants offer tempura as part of a set meal or a bento (lunch box), and it is also a popular ingredient in take-out or convenience store bento boxes.
Outside of Japan, tempura (particularly shrimp) is often used a filling in makizushi. A more recent variation of tempura sushi has entire pieces of sushi being dipped in batter and tempura-fried. The ingredients and styles of cooking and serving tempura vary greatly through the country, with importance being placed on using fresh, seasonal ingredients.
Outside Japan, restaurants sometimes use broccoli, zucchini and asparagus. There are many non-traditional and fusion uses of tempura. Chefs over the world include tempura dishes on their menus, and a wide variety of different batters and ingredients are used. Variations include using panko or corn flour, however, the consistency is crisper using panko as opposed to tempura batter, and frying unusual ingredients such as nori slices, non-watery fruit such as banana, and ice cream.
In northern Taiwan, tempura is also known as 天婦羅 or 甜不辣 (tianbula) and can be found at night markets such as Shilin Night Market and Keelung Temple Night Market, where it is famous. The ingredients and method used for making Taiwanese tempura are completely different from Japanese tempura, and they share only the name. In southern Taiwan, however, it is known as 黒輪 or 和田 and is more the counterpart to oden. Oden is generally known as 關東煮 or "Kwantung cooking" in reference to the Kwantung (Kantō) region of Japan.