Sushi and Ketchup — an unlikely pair

Their common origin in fermented fish

3 min readOct 18, 2021
Photo by Louis Hansel on Unsplash

Sushi and tomato ketchup represent two culinary extremes — one associated with refined healthy eating and the other with American junk food. But remarkably, they share a common origin: fermented fish. It all began with the Chinese, as, in historical terms, almost everything did.

In river and coastal regions of southern China, small fish were plentiful in season, but needed to be preserved for the off-season. In that humid climate, preservation by dehydration was not an option, and the Chinese turned to fermentation instead.

Fish were layered between cooked rice and wrapped in leaves. Enzymes and bacteria in the fish broke down starch in the rice, producing lactic acid that in turn preserved the fish. Liquid generated by this process was drawn off as fish sauce. The fish itself was preserved and soft. The rice was inedible and discarded.

The fish sauce was a most desirable by-product. As political upheavals in China forced ethnic groups to move south (Thailand, Vietnam, Burma) they took fish-sauce technology with them. From there fish sauce moved south as far as Indonesia, where the first Europeans (Dutch) were introduced to it.

Sailors in particular liked fish sauce because it lasted for long sea voyages and added flavour to their otherwise repetitive and tasteless preserved food.

Thus it was transported to Europe and became highly appreciated and priced accordingly. This in turn led Europeans to attempt imitations and variations that did not need to be transported from Asia. Worcestershire sauce was a later example. Meanwhile the sauce was adulterated with various additives — mushrooms, hazelnuts… and finally and most successfully — tomatoes.

As it moved trans-Atlantic, the Americans further modified it, thickening and sweetening an otherwise savoury sauce to suit their taste and purpose. Tomato ketchup was born. So much so that its name is now almost a tautology — ketchup is synonymous with tomato sauce.

Nevertheless, the word ketchup retains its more respectable origins. Capturing the sound of the Chinese word (across dialects) for fish sauce in European languages was difficult, but resulted in variations on the word ke-tchup (ke fermented fish; tchup sauce).

While the Romans had developed a similar process to produce a savoury fish sauce called garum, the practice expired with empire.

And sushi? The practice of fermenting fish in rice spread in all directions, reaching Japan. The Japanese decided they liked their fish a little less preserved. This meant that the rice was less fermented and could be eaten. In time this preference reached its logical conclusion and the fish began to be eaten raw (fish preservation was less important given the fertile waters around Japan). The rice was consequently unfermented, so it was re-acidified with rice vinegar (sushi translates as ‘sour’), with a little sugar to balance. The savoury (umami) flavour of the fish was lost in this process, so it was added back in using one of the main available sources of glutamate — seaweed (in the form of a wrapping). The fermenting process was maintained for soy beans (as it was elsewhere), producing soy sauce for dipping and added savoury flavour.

Today, the machine-made mass produced sushi that we find in most lunch bars is maki-zushi (rolled sushi), or more likely it will be nori-maki (the same principle but more rice and less filling). Hand-formed rice topped with seafood is nigiri-zushi (hand-shaped). The variations are endless, but in all cases it is about the rice. As with most Asian cuisines, the rice is the meal.

The fermented rice thrown away during fish preservation thus became the focal point of the preparation in Japan with fish-preservation omitted altogether. Meanwhile, in America, ke-tchup morphed into a sweet tomato sauce retaining its heritage in name only. Two diverging lines of cuisine with an unexpected common ancestor.

Everything is a remix.

Further reading: Dan Jurafsky ‘The Language of Food‘. WW Norton & Co., NY




Science of cooking, eating and health. Retired neuroscientist.