A fish sauce discovered by British sailors
"Ketchup" sold today has very little (or nothing) to do with the origins of ketchup. Although the exact origin of the sauce and its name are disputed to this day, some facts are rather certain: During their journeys to Asia in the 17th century, British sailors discovered a savory sauce that local sailors used to take on their long journeys in order to spice up the bland food at sea. It is interesting to note that this sauce was made from fermented and salted fish that was placed in a clay pot and put under the sun for several weeks, resulting in a concentrated fish sauce.
The name originates in Asia
A possible explanation for the origin of the word "ketchup" goes into the same direction: Some believe that it is derived from the Hokkien Chinese word "kê-tsiap", meaning a "brine of pickled fish". But how did this fermented fish sauce - or the name of it - turn into today's "ketchup"? Upon returning to Europe, the British sailors spread the news about this savory sauce and a number of producers in Britain subsequently tried to copy the recipe. They used oysters, walnuts or mushrooms as a base to copy the black and thin sauce which in taste and texture was somewhat similar to today's soy sauce.
Scaling it up in the USA
It is owed to the old world-new world trade routes that with time, "ketchup" became known as a table sauce in the United States, at first however only as a niche product. This was quickly going to change when in 1812 in Philadelphia, scientist and passionate horticulturist James Mease published the first known ketchup recipe using tomatoes. At that time, tomatoes were far and wide considered to be inedible - but then quickly became very popular in the United States around 1830 (in Europe, this only happened decades later). The first tomato ketchups quickly became very popular and were even sold as panacea with healing powers (stomach ache, hair loss?).
The seeming healing properties, however, stood in stark contrast with the fact that "ketchups" produced at that time contained toxic amounts of bacteria, spores and dangerous concentrations of coal tar and sodium benzoate as preservatives. These "ketchups" - preserved due to the short tomato harvesting season - were hazardous to health and remained to be so until the food industry made significant progress in the preservation of products at the end of the 19th century.
Improvised recipe becomes tradition
In 1876, a certain Henry J. Heinz appeared on the scene of the quickly growing American preserved food industry. His philosophy: To create a "ketchup" without dangerous additives and preservatives. In order to achieve this, Heinz however had to significantly increase the level of acidity in his "ketchup" recipe (thus adding a lot more vinegar) - and in order to balance the acidity, also add great amounts of sugar to make his product edible.
Surprisingly, the basic recipe for "ketchup" has not changed significantly since then. In consequence, almost every household today uses a table sauce made from a recipe that was not primarily created because of its great taste, but because it was safe to eat.