On any fine day in spring, when the sky is clear and the waters of nearby Lake Biwa are calm enough for locals to go carp fishing, you can find Mariko Kitamura and her husband Atsushi at their shop Kitashina in the small Japanese town of Takashima making sushi.
With the dexterity and speed you'd expect from sushi chefs, they scrape off the fish's scales with a knife, remove its gills and carefully angle a skewer down its throat to remove its innards without penetrating its flesh. But what happens next is truly unexpected. They pack the fish with salt, layer them in a wooden tub, weigh the lid down with 30kg stones and leave them to cure for two years. Each fish is then thoroughly rinsed, dried in the sun for a day and fermented for one more year in cooked rice before it is ready to be eaten.
In Kitashina's storeroom, 30kg stones weigh down wooden tubs packed with salted, curing fish (Credit: Tom Schiller)
This is not the kind of sushi you might get in New York or London, or even easily in Tokyo for that matter. It is the predecessor of what the world now knows as sushi – the original sushi – called narezushi (fermented sushi). Kitamura's family has been making it for 18 generations, ever since Kitashina opened in 1619 in this remote corner of Shiga prefecture, and today the centuries-old shop is one of a handful of places left in Japan, and the world, where you can experience how "real" sushi is supposed to taste.
Narezushi is thousands of years old and traces its roots back to the rice fields of China, where the method of curing in salt and fermenting the freshwater fish that lived in the paddies was developed to give the seasonal catch a long shelf life. It is believed to have arrived in Japan at the country's ancient capital of Nara sometime in the 8th Century. For the next 1,000 years, until it evolved in the 18th Century into the slices-of-raw-seafood-draped-over-mounds-of-rice dish we know today, narezushi was a commonly consumed, nourishing and tasty source of protein. People would eat a few pieces of it with the fermented rice. They'd put a slice of it in hot water to make a medicinal tea. And they enjoyed it as a delicacy with sake at the tables of aristocratic and samurai families.
As a testimony to narezushi's importance and the skill required to make it, Kitamura's ancestor 18 generations back, Kuemon Yamagataya (Kitashina's founder), was appointed to the entourage of Lord Mitsunobu Wakebe when he moved to Takashima in 1619 to take charge of the castle at the request of Japan's new military leader, Ieyasu Tokugawa.
Unlike modern sushi, which typically includes ocean seafood, Narezushi was made – and still is in small pockets of Japan – with pretty much anything that swims in fresh water, including tiny loach, ayu (small sweet fish) and eel. But the kind of narezushi Kitashina makes is much rarer and is considered the true prototype of sushi. It is called funazushi after the type of fish used: funa (carp).
Kitashina’s signature dish is a platter of funazushi made from roe-laden female carp served as fanned slices of the whole fish on a bed of sake lees (Credit: Tom Schiller)
Carp is the king of freshwater fish in Japan, with the most prized being Japanese crucian carp (nigorobuna), which is the original type of carp used to make funazushi and the kind Kitashina features. It is a wild, rich-tasting species that's found only in Lake Biwa, Japan's largest lake and one of the oldest lakes in the world.
Today, there are just five shops around the lake that specialise in making high-quality funazushi, as nigorobuna has become very rare and hard to obtain. Other places, including souvenir shops across the prefecture, use more common types of carp and offer a comparatively ready-made version – funazushi cured in salt for one summer and fermented in rice for a few months in autumn – for tourists seeking to try its reputedly pungent taste. Among them all, Kitashina is the one making the most authentic funazushi by using nigorobuna and applying the oldest, most traditional preparation methods.
The good stuff is hard to get, though. Peak demand for Kitashina's funazushi is from November to February when customers order it as a New Year's treat, and later, to celebrate the arrival of spring. It can be sold out then, but a fresh batch, so to speak, is ready every year in mid-summer.
Before trying funazushi, Kitamura told me that it tastes like cheese – which it does, in its lacto- fermented, sour, salty and umami-rich way. It's reminiscent of a funky and creamy type of cheese, given that Kitashina makes funazushi with the roe-laden female nigorobuna in season from March to May. Like many mature cheeses, funazushi is an acquired taste; a food that takes some getting used to. But then so is eating raw seafood for many people.
Kitamura is the 18th generation in her family to run Kitashina, and she took over the family business to preserve its authentic way of making funazushi (Credit: Tom Schiller)
Kitamura, who attended the Kyoto Culinary Institute, took over the family business in 2013 when her father was ready to retire – partly because of her interest in food, but more importantly, to save the business from, literally, dying out. The beneficial micro-organisms that have thrived in her family's traditional kioke wooden tubs for centuries, and which naturally produce the fermentation that gives Kitashina's funazushi its authentic flavour, would die if the tubs were ever emptied.
Today, funazushi has become a luxury food across much of Japan, with Kitashina being the shop at which to buy it because of its refined, mellow flavour. According to Kitamura, that's in part thanks to her grandfather, who, despite sushi's growing popularity, continued to stick to Kitashina's 400-year-old recipe of long fermentation and changing the rice once during the process. He also introduced the practice of serving it on a bed of sake lees – the sweet, rich paste left after pressing sake from the fermented rice mash – making the dish even more luxurious. Kitamura's father, in turn, created the "Tomoe" style of beautifully presenting funazushi as a fan fashioned from the slices of a whole fish.
Kitashina's funazushi is now featured on the menus of some of the most exclusive ryotei (traditional high-end Japanese eateries) and other top restaurants in Kyoto, as well as at similar establishments in Tokyo. Taking a cue from Kitamura's grandfather's presentation, chef Takumi Murata, of the L'Hotel de Hiei located atop the historical Mount Hiei overlooking Kyoto, serves Kitashina's funazushi with wine jelly as an appetiser in the hotel's main restaurant.
Kitashina's funazushi is now featured on the menus of some of the most exclusive restaurants in Kyoto and Tokyo (Credit: Tom Schiller)
Compared to narezushi's millennia-old history, the sushi we eat today is a mere footnote. Technically called hayazushi (fast sushi), it was created in Edo (modern-day Tokyo) in the late 18th Century as a fast-food version of narezushi to meet the needs of the city's busy people. The newly bottled seasonings of fermented rice vinegar and soy sauce were used to recreate the essential sour, salty and rich taste of funazushi in the fresh seafood that was caught in Tokyo Bay. First, rice vinegar was added to cooked rice to speed up the fermentation process to just a few days. This practice also made the rice more edible. Later, freshly cooked rice was simply soaked with rice vinegar.
The gamechanger, however, was soy sauce, which began to be mass produced in the 1700s. As Issei Tomioka, a former employee at the Tokyo Metropolitan Central Wholesale Market in Tsukiji, wrote in his series The History of Nihonbashi Uogashi, "sushi would likely not have been developed had it not been for soy sauce." Brewed for at least two years, traditional soy sauce is a concentrated form of salty-savoury umami. Initially, it was used to marinate the seafood toppings for a few hours to prevent them from spoiling and also to make them more appetising. As the fresh quality of the seafood improved, sushi was served raw with soy sauce as a condiment.
Sushi is a remarkable example of the way Japan adopts foods from other countries, in this case China, and then adapts and assimilates them into its own rich culinary culture. After thousands of years, sushi continues to evolve.
The sushi we eat today is called hayazushi (fast sushi) and was created as a fast-food version of narezushi for Tokyo's busy people (Credit: Ruben Earth/Getty Images)
Currently, the pendulum is swinging backwards, and sushi chefs in Japan are now aging their seafood toppings for days, weeks and even months to give all kinds of fish the creamy texture and savoury richness of funazushi. Koji Kimura, chef-owner of the two-Michelin-starred Sushi Kimura in Tokyo's Setagaya ward, has been serving only aged sushi since 2008 and is considered its modern-day pioneer.
Closer to Takashima, Yoichi Akashi, the chef at Sushi Zabo in Miyazu City, is following the tradition of Kitashina's funazushi by taking an already rich-tasting, fatty fish like akamutsu (rosy seabass) caught fresh from the nearby Sea of Japan, and making it even more luscious through aging.
But even as chefs rediscover the potential of weeks- and months-aged sushi, Kitamura is staying well ahead of them. In a corner of Kitashina's storeroom, she has a small wooden tub of funazushi that has been fermenting for eight years and counting.
As funazushi is coming back in fashion, chefs across Japan are now aging their sushi for longer periods (Credit: Kitashina)
Culinary Roots is a series from BBC Travel connecting to the rare and local foods woven into a place’s heritage.
If you liked this story, sign up for the weekly bbc.com features newsletter called "The Essential List". A handpicked selection of stories from BBC Future, Culture, Worklife and Travel, delivered to your inbox every Friday.