A documentary about 85-year-old Jiro Ono, said to be the world's greatest sushi chef, was one of the hottest tickets at the recent Shanghai Film Festival.

"Jiro Dreams of Sushi" tells the story of the master who ran away from home as a boy and became an apprentice in a restaurant making sushi. Today, the unassuming Ono presides over Sukiyabashi Jiro, a 10-seat, sushi-only restaurant inauspiciously located in a Tokyo subway. It has three Michelin stars.

Chef Ono interprets sushi as a kind of manipulation of raw fish as an art form, in which every step of food preparation - selection of ingredients, to slicing, carving, molding rice, and presentation - is based on perfect calculation.

This reverence for sushi and dedication of one's life to preparing visually- and palate-pleasing dishes is not exclusive to chef Ono. For many sushi chefs, sushi is almost a religion and certainly a discipline.

This week, we interview top sushi chefs in Shanghai's five-star hotels, discovering the secrets behind the exquisitely prepared and presented seafood and cooked vinegared (shari) rice.

"Sushi is actually not as simple as it seems," says Eric Zhang, J Mix Japanese chef at Jumeirah Himalayas Hotel Shanghai, with 22 years' sushi-making experience.

"To the contrary, sushi is the product of an experienced chef's precise calculation in terms of cutting, flavoring, texture molding as well as serving and getting the temperature right."

Temperature is considered key to perfect sushi taste.

"The golden temperature is around 37 degrees Celsius, known in the profession as 'human skin temperature,'" chef Zhang says.

According to chef Zhang, the temperature helps the cooked vinegared rice maintain its best texture, which is a bit bouncy, moderately sticky vinegar-flavored. Temperature also highlights the taste of neta, the various ingredients placed on the rice, usually raw seafood.

"Take raw sea fish such as salmon and tuna as an example. If the fish is served above 37 degrees Celsius, the flesh will tastes soft, losing its freshness and firm texture," the chef says.

Thus, to maintain the right temperature, a sushi chef should prepare sushi as quickly as possible to avoid the ingredients being warmed by the palm temperature, he adds.

Precise slicing and cutting is crucial; the size and thickness of the fish being cut should be controlled precisely or the taste may be ruined, he explains.

Size and thickness depend on the chef's understanding of various seafood textures. Salmon, which is soft and contains fat, is best cut in thick pieces to highlight its texture, while for firm-textured fish, such as flatfish, thin slicing ensures good taste and easy biting texture.

Sushi is known for its rice with sweet, sour and slightly salty flavors, achieved by using sugar, vinegar and salt. According to chef Zhang, good sushi has a balanced taste, which means the three flavors coexist harmoniously without a dominant note; this requires a precise flavoring process, held by many sushi chefs as their secret.

In Japan, the cradle of sushi, there are hundreds if not thousands of sushi varieties and possibilities, based on different toppings and preparations.

But in Shanghai, from small restaurants and convenience stores to high-end venues, there are generally four types of sushi.

Nigrizushi is popularly known as sushi, consisting of rice pressed by the chef into small rectangles and topped with neta, usually raw fish. This is considered representative of authentic Japanese sushi culture, demonstrating the chef's multiple skills.

Makizushi, known as a sushi roll, is a cylindrical rolled sushi wrapped in seaweed and containing cooked ingredients for easy carrying and brief storage.

Oshizushi is compact sushi pressed into a block shape.

California roll is adapted American taste; it's a sushi roll made with cooked food, such as crab, and ingredients such as avocado.

New sushi menus for summer have recently been launched by Eric Zhang from Jumeirah Himalayas and Hiroyuki Hirobe from Sunrise on the Bund.

Chef Zhang adds modern twists to traditional flavors, while chef Hirobe preserves authentic flavors and methods of his hometown Tokyo in Japan.

Sushi set

(268 yuan/US$44.9+15 percent)

The set menu launched by chef Hirobe follows the traditional Japanese sushi bar dining culture known for close interaction between chef and customers and customized service.

Diners sit at the sushi counter and watch the chef cut the ingredients, shape the rice and then present the plate. The menu is general, saying simply sushi and sushi roll.

All are made with the best fresh daily ingredients.

But diners can talk to the chef and describe their preference.

According to chef Hirobe, for female guests, the chef usually makes small sushi; for those ordering strong sake, the chef serves sushi with a rich taste; for Westerners not adept with chopsticks, the chef presses the rice firmly so it can be picked up by hand.

Although there's not a fixed menu, salmon, tuna and shrimp are in relatively good supply. The set menu includes a seasonal appetizer, sushi, sushi roll, soup, fruit and dessert.

Venue: Sho-U tou, Sunrise On the Bund

Tel: 5558-9999 ext 6718

Address: 168 Gaoyang Rd

Huozhuo (?e×?) sushi

(200 yuan+15 percent)

Huozhuo sushi is made by passing the flame of a butane torch briefly over the neta, or ingredients, which gives the raw fish a slightly crispy texture outside, while it remains creamy inside.

"It's the latest sushi trend in Japan," chef Zhang says. "Usually we use ingredients with thick fat as the neta and use the flame to release the fat."

This sushi plate contains five different kinds of ingredients, including scallop, abalone, salmon, mackerel, foi gras and wagyu beef.

For the sushi with fatty ingredients, the chef sprinkles them with pomelo-flavored vinegar to cut through the fat.

Vegetarian sushi

(150 yuan+15 percent)

Inspired by the trend of light and healthy eating, chef Zhang creates a sushi plate containing five different kinds of sushi, most made with vegetables and vinegared rice. They include inarizushi, a pouch of fried tofu filled with a rice ball mixture with shredded carrot; xianggu, a delicate-flavored mushroom and 'skin' of a bottle gourd; asparagus sushi; bailinghu, a mushroom with an abalone-like texture); moyu, a kind of devil's tongue plant with a silky texture; soba, or buckwheat noodle (in this case no rice). It's not necessary to dip these sushi in soy sauce and wasabi horseradish since chef Zhang has already flavored them during cooking.

Mango sushi with tempura soft shell crab

(120 yuan+15 percent)

This is a kind of California roll with the rice on the outside and seaweed inside. Tempura soft shell crab, avocado and shredded cabbage are wrapped in rice, creating various textures, crispy, crunchy and soft. It's topped with mango paste, adding a sweet and sour taste, balancing the oily crab and rich avocado.

Venue: J Mix, Jumeirah Himalayas Hotel

Tel: 3858-0888

Address: 1108 Meihua Rd