Unlike champagne and asiago cheese (and scores of other foods and drinks), which must be made in a certain area to be considered the real thing (and labeled as such), Dijon mustard does not have to be made in Dijon, France.

In fact, most of the world's Dijon mustard is not made in Dijon, France.

So what makes a Dijon a Dijon? Well, all mustard is made by mixing ground mustard seeds (white, yellow, brown, or black) with vinegar, water, grape must, and other liquids. What makes a mustard a "Dijon mustard" is the use of wine must and white wine which -- in combination with brown and/or black mustard seeds, cloves, cinnamon and other spices and herbs -- give Dijon mustard its distinctive tangy flavor.

Reference: What does "emulsify" mean?
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