Short answer
It depends on the label. Many Dijon mustards are made with white wine, and wine added as an ingredient makes a food haram in the Hanafi school and the other schools. Dijon made with vinegar, wine vinegar or verjuice (unfermented grape juice) instead of wine is halal. Read the ingredients.
If the ingredients list wine, the mustard is not halal: wine is khamr, impure and forbidden in any amount, and it does not become vinegar by being mixed into mustard. Mustard made with vinegar or verjuice is halal.
The four schools agree on this.
Explanation
Dijon mustard is made from brown mustard seeds and an acidic liquid. Traditionally that liquid was verjuice, the sour juice of unripe grapes, which is not fermented and is halal. Many modern recipes use white wine instead, or as well, and some use wine vinegar. The word Dijon describes the style, not one fixed recipe, so two jars side by side can have different rulings.
How to read the label:
- White wine or wine: not halal.
- White wine vinegar or vinegar: halal, since wine that has fully turned into vinegar is pure in the Hanafi school (see balsamic vinegar).
- Verjuice or grape must: halal.
- Ingredients not listed, as in restaurant dressings and sauces: ask.
Some people argue that the wine in mustard is such a small amount that it does not matter. The four schools agree that wine is forbidden in small amounts as well as large, and it was added on purpose, so the argument does not hold (see food made with wine).
Other mustards, such as American yellow mustard, English mustard and wholegrain mustard, are usually made with vinegar and are halal, but wholegrain and honey mustards sometimes contain wine or beer too. Recipes change, so check the jar you are buying, or use the halal food checker.
Ask a mufti about your own case. This answer explains the general ruling. When the details of your situation matter, as they do here, ask a qualified mufti and give them the full facts. Where to ask a scholar.
The evidence
Quran, Surah Al-Maaida 5:90
يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوٓا۟ إِنَّمَا ٱلْخَمْرُ وَٱلْمَيْسِرُ وَٱلْأَنصَابُ وَٱلْأَزْلَٰمُ رِجْسٌۭ مِّنْ عَمَلِ ٱلشَّيْطَٰنِ فَٱجْتَنِبُوهُ لَعَلَّكُمْ تُفْلِحُونَ ﴿٩٠﴾
O you who have believed, indeed, intoxicants, gambling, [sacrificing on] stone alters [to other than Allah], and divining arrows are but defilement from the work of Satan, so avoid it that you may be successful.
Wine is to be avoided, including as an ingredient.
Sunan Abi Dawud 3681
Graded hasan sahih... ما أسكر كثيره فقليله حرام ...
"Whatever intoxicates in a large amount, a small amount of it is haram."
A small amount of wine in a recipe is still forbidden.
Where the ruling is recorded
- al-Hidaya, Kitab al-Ashriba. Wine is forbidden in any amount and is impure; vinegar made from it is pure.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Ashriba. Food mixed with wine takes its ruling.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.