The name may come from that of a type of dark-red grape, now rarely grown.
Original Receipt in 'A New System Of Domestic Cookery' by 'A Lady' (Mrs. Maria Eliza Ketelby Rundell) (Rundell 1807);PONTAC KETCHUP FOR FISH.
Put ripe elderberries, picked from the stalk, into a stone jar, with as much strong vinegar as will cover them. Bake with the bread; and, while hot, strain. Boil the liquor with a sufficient quantity of cloves, mace, peppercorns and shalots, to give it a fine flavour. When that is obtained, put in half a pound of the finest anchovies to every quart of liquor: stir, and boil only until dissolved. When cold, put it into pint bottles, and tie double bladders over each cork. The same method should be observed for preserving all ketchups.