Modern sushi, featuring fresh fish on vinegared rice, is a relatively recent invention. Its ancestor, 'Narezushi,' dates back over a thousand years and was a method of preserving fish. Raw fish was packed with salt and fermented rice; as the rice fermented, it produced lactic acid, which preserved the fish and kept it safe for months. Originally, the fermented rice was discarded, and only the sour fish was consumed. By the Edo period (1603–1867), Japanese people began adding vinegar to the rice to mimic the sour taste of fermentation without the long wait time, allowing both the fish and the rice to be eaten together. This evolved into 'Nigirizushi' in the 1820s—fast food sold at street stalls in Tokyo (then Edo)—which is the direct ancestor of the sushi we recognize today.