This is mostly conjecture, but one of the flavors I've been able to detect in
Coca-Cola is an unexpected, but logical one:
Riesling, as in the
wine or
grapes. This has led me to the following speculation: it's a fact that Coca-Cola is ersatz
Mariani Wine, a cocaine-laced beverage (think
Bawls on
steroids) of the late 19th century. An extract of wine grapes (even more than the
cocaine) would be suspect in some
Prohibitionist quarters in America (
dry counties, sales to children, "Negroes", "Indians", etc.) Therefore, by claiming a "secret" ingredient, the Coca-Cola company could market their product as a "
temperance" drink, with no such problems.
My opinion only, YMMV.