Onigiri

Onigiri (お握り or 御握り), also known as omusubi (お結び), nigirimeshi (握り飯), or rice ball, is a Japanese food made from white rice formed into triangular or cylindrical shapes and often wrapped in nori. Onigiri traditionally have sour or salty fillings such as umeboshi (pickled Chinese plum), salted salmon, katsuobushi (smoked and fermented bonito), kombu, tarako or mentaiko (pollock roe), or takanazuke (pickled Japanese giant red mustard greens). Because it is easily portable and eaten by hand, onigiri has been used as portable food or bento from ancient times to the present day. Originally, it was used as a way to use and store left-over rice, but it later became a regular meal. Many Japanese convenience stores and supermarkets stock their onigiri with various fillings and flavors. It has become so mainstream that it is even served in izakayas and sit-down restaurants. There are even specialized shops which only sell onigiri to take out. Due to the popularity of this trend in Japan, onigiri has become a popular staple in Japanese restaurants worldwide.

Despite common misconceptions, onigiri is not a form of sushi and should not be confused with the type of sushi called nigirizushi or simply nigiri. Onigiri is made with plain rice (sometimes lightly salted), while sushi is made of rice with vinegar, sugar and salt. Onigiri makes rice portable and easy to eat as well as preserving it, while sushi originated as a way of preserving fish.

History
Before the use of chopsticks became widespread, in the Nara period, rice was often rolled into a small ball so that it could be easily picked up. In the Heian period, rice was made into small rectangular shapes known as tonjiki so that they could be piled onto a plate and easily eaten. At that time, onigiri were called tonjiki and often consumed at outdoor picnic lunches.

The first incarnation of the word onigiri is attested in the "Hitachi Province Gazette" (常陸国風土記 Hitachi no Kuni Fudoki) dated to 5 Yōrō (721 AD) as 握飯 nigiri-ihi or "crumpled rice": In Murasaki Shikibu's 11th-century diary Murasaki Shikibu Nikki, she writes of people eating tonjiki rice balls. Other writings, dating back as far as the seventeenth century, state that many samurai stored rice balls wrapped in bamboo sheath as a quick lunchtime meal during war.

From the Kamakura period to the early Edo period, onigiri was used as a quick meal. This made sense as cooks simply had to think about making enough onigiri and did not have to concern themselves with serving. These onigiri were simply balls of rice flavored with salt. Nori did not become widely available until the Genroku era of the mid-Edo period, when the farming of nori and fashioning it into sheets became widespread.

Excavated from the Sugitani Chanobatake Ruins
On November 12, 1987, lumps of carbonized grains of rice, thought to be riceballs, were excavated from a building belonging to the Yayoi period (2000 years ago) in the Sugitani Chanobatake Ruins in Ishikawa Prefecture. The carbonized rice had traces which revealed that it was formed by human hands, thus it was initially documented as "the oldest onigiri." In subsequent research, it was thought to be steamed and grilled, rather than boiled like today's rice, similar to another dish called chimaki. Since then, it has been academically called the "Chimaki-shaped carbonized rice lumps (チマキ状炭化米塊)".

In Nakanoto, there is a replica of the relic on display at the roadside station Orihime-no-sato Nakanoto.

Mass manufacturing
In the 1980s, a machine to make triangular onigiri was invented. Rather than rolling the filling inside, the flavoring was put into a hole in the onigiri and the hole was hidden by nori. Since the onigiri made by this machine came with nori already applied to the rice ball, over time the nori became moist and sticky, clinging to the rice.

A packaging improvement allowed the nori to be stored separately from the rice. Before eating, the diner could open the packet of nori and wrap the onigiri. The use of a hole for filling the onigiri made new flavors of onigiri easier to produce as this cooking process did not require changes from ingredient to ingredient. Modern mechanically wrapped onigiri are specially folded so that the plastic wrapping is between the nori and rice to act as a moisture barrier. When the packaging is pulled open at both ends, the nori and rice come into contact and are eaten together. This packaging is commonly found for both triangular onigiri and rolls (細巻き).

Rice
Usually, onigiri is made with boiled white rice, though it is sometimes made with different varieties of cooked rice, such as:
 * O-kowa or kowa-meshi (sekihan): glutinous rice cooked or steamed with vegetables (red beans)
 * Maze-gohan (lit. "mixed rice"): cooked rice mixed with preferred ingredients
 * Fried rice

Fillings
Umeboshi, okaka, or tsukudani have long been frequently used as fillings for onigiri. Generally, onigiri made with pre-seasoned rice is not filled with ingredients. Plain (salt only) onigiri is called shio-musubi.

Typical fillings are listed below:
 * Dressed dishes: tuna with mayonnaise (シーチキン), shrimp with mayonnaise, negitoro (ネギトロ), etc.
 * Dried fish: roasted and crumbled mackerel (鯖), Japanese horse mackerel (鰺), etc.
 * Kakuni: dongpo pork
 * Dried food: okaka, etc.
 * Processed roe: mentaiko (明太子), tarako (たらこ), tobiko (とびこ), etc.
 * Shiokara: squid, shuto, etc.
 * Tsukudani: nori, Hypoptychus dybowskii (小女子), Venerupis philippinarum (浅蜊), etc.
 * Pickled fruits and vegetables: umeboshi, takana, nozawana, etc.

Yaki-onigiri
Yaki-onigiri (焼きおにぎり) or grilled rice balls is first shaped by compacting white rice, then grilling it until brown, then coating with soy sauce or miso, and finally broiling it. Yaki-onigiri is also sold commercially as frozen food.

Miso-onigiri (味噌おにぎり) is mainly in eastern Japan. Miso is used as fillings, sometimes mixed with green onion, or spread over and roasted as a variant of Yaki-onigiri.

Age-onigiri
Age-onigiri (揚げおにぎり) or fried rice balls is first shaped by compacting white rice, then frying it in a frying pan or wok using cooking oil until it is golden brown. Because of the oil, the flavor is richer than yaki-onigiri. If eating it as is, it can be seasoned with soy sauce, miso, or salt.

To eat it in a soup, first place it in a bowl. Add condiments such as chives, miyakogusa, wasabi, grated ginger, nori, pickled plum, and pour hot Japanese-style soup stock. Eat while breaking up the onigiri that have absorbed the soup stock.

There are several variations of the age-onigiri. For example, there is a version where the rice being fried has Japanese flavoring, such as takikomi gohan. There is also a Western style variation where melted cheese is used as the filling, the rice is deep-fried with western ingredients such as ketchup and curry, and the onigiri is topped with a western-style soup.

Pork egg onigiri
Pork egg onigiri (ポーク玉子おにぎり or おにポー) is a variation from Okinawa Prefecture which combines rice, seaweed, pork, and eggs. It is similar to onigirazu, which is described later, but this variation came first.

Other

 * Tenmusu (天むす): originally in Tsu, Mie. became famous as Nagoya cuisine.
 * Pork-tamago-onigiri (ポークたまごおにぎり): in Okinawa. Lunch meat and fried egg as fillings.
 * Samgak-gimbap (삼각김밥) — Literally "triangle gimbap". It originates from Japanese onigiri and is sold in convenience stores in South Korea. Fillings vary greatly; the expiration date is one day; it typically provides between 140 and 200 kcal of food energy.