Proper Dijon mustard does not contain vinegar.

French Dijon mustard is a smooth, mild mustard which in general does not override the flavours it is combined with. Made in the town of Dijon in the region of Burgundy, moutarde à la Dijonnaise is unique in that is made from mustard grains made with verjuice (the juice of sour Burgundy grapes), plus herbs and other flavourings. Most mustards are made with vinegar, which is why they are sharper in flavour.