Sour-sweet tomato ketchup began as a humble fermented fish sauce off the southern coast of China thousands of years ago as a way to make food last during the dry season. Across oceans, centuries and cultures it evolved into the mass-produced sauce we know so well today.
Before 200 BCE
The Yi people preserved food by layering fish, rice and salt — a process that produces a pungent sauce. Many of these people later moved into southeast Asia.
Fujianese traders and seamen in the bustling ports fell for the stuff, naming it ke-tchup, meaning preserved-fish sauce.
Fujianese settlers set up Chinese sauce-making factories, and British sailors discovered the fish sauce and flavored their hardtack with it.
ketchup, chatchup, catsup
British sailors brought the sauce home. The British recipe evolved to include mushroom and tomatoes and exclude fish.
The American recipe became thicker and sweeter than its British cousin, and cooks added more sugar and vinegar.
Source: The Language of Food: A Linguist Reads the Menu by Dan Jurafsky