The basic concept of fish preparation in Japan is suggested by the following proverb: "Eat it raw first of all, then grill it, and boil it as the last resort." To amplify, it is felt that the taste and texture of fish is best appreciated when it is very fresh and eaten raw. If the fish is a little less than fresh then its best taste will be produced by sprinkling it with salt and grilling it. If the fish is not fresh, then it is better boiled with seasonings, such as soy sauce or soybean paste (miso).
Nigiri-sushi, prepared by putting a slice of raw fish onto a bite-size portion of hand-rolled, vinegar-flavored rice, has recently become internationally popular. But sushi originated as a means of preserving fish by fermenting it in boiled rice. Fish that are salted and placed in rice are preserved by lactic acid fermentation, which prevents proliferation of the bacteria that bring about putrefaction. A souring of flavor occurs during the process, and the fish is eaten only after the sticky decomposed rice has been cleaned off.
This older type of sushi is still produced in the areas surrounding Lake Biwa in western Japan, and similar types are also known in Korea, southwestern China, and Southeast Asia. In fact, the technique first originated in a preservation process developed for freshwater fish caught in the Mekong River and is thought to have diffused to Japan along with the rice cultivation.
A unique fifteenth-century development shortened the fermentation period of sushi to one or two weeks and made both the fish and the rice edible. As a result, sushi became a popular snack food, combining fish with the traditional staple food, rice. Sushi without fermentaion appeared during the Edo period (1600-1867), and sushi was finally united with sashimi at the end of the eighteenth century, when the hand-rolled type, nigiri-sushi, was devised.
Various styles of hand-rolled sushi were developed, such as norimaki, in which vinegar-flavored rice and seasoned boiled vegetables are rolled in paper-thin layers. In addition, sushi restaurants became popular during this era. They offered seasonings and rolled with different toppings according to the taste of the guests. In this manner, sushi has changed from its original character as a preserved food to that of a fast food.