Here's why:
* Proper Nouns: Dijon is a proper noun, a specific name of a person, place, or thing. Proper nouns are always capitalized.
* City Names: City names are always capitalized, regardless of whether they are used in a sentence or as part of a longer phrase (e.g., "The city of Dijon", "Living in Dijon").
However, you don't need to capitalize "dijon" when referring to the mustard:
* Common Noun: "Dijon" as a type of mustard is a common noun, not a specific name. Common nouns are not capitalized unless they are at the beginning of a sentence.
Examples:
* Capitalized: "We visited the city of Dijon and sampled some delicious Dijon mustard."
* Not Capitalized: "I like to put dijon mustard on my sandwiches."