Ketchup is made from just a few ingredients: lots of tomatoes, a touch of white vinegar, some corn syrup, salt, and natural flavorings. From late August to early October, most ketchup is made from fresh tomatoes. The rest of the year, tomato paste is used instead of fresh tomatoes, with no discernible taste difference. Every manufacturer's recipe varies slightly, and there are differences from country to country. Heinz, for example, produces a sweeter ketchup for the English than for us, while for Central Europeans the formula is made spicier. The exact Heinz recipe is a closely held secret, although some years ago we discovered that clove oil gives the brand its unique flavor.