Add all the ingredients to a small, non-reactive saucepan and whisk until it’s smooth and well combined.
Bring the mixture to a slow boil over low heat, whisking to ensure it doesn’t stick to the pan
Let it simmer for 8-15 minutes, stirring every minute to maintain a smooth consistency. You might need to turn the heat down to prevent it from bubbling out of the pan. Stir often to prevent this. Do not put a lid on, it will draw moisture and make your mustard watery.
Remove the pot from the heat and allow it to cool to room temperature. Once the mustard is at room temperature, you are ready to cure it. This is where the flavor magic happens. You can choose between two methods for curing the mustard.
Curing at room temperature: Allow the mustard to sit at room temperature for 8 to 10 hours before refrigerating. This will result in a milder and smoother flavor similar to store-bought squeeze bottle mustard.
Curing in the refrigerator: Transfer the mustard to sterilized glass jars, secure the lids, and place the jars in the refrigerator for 24 to 48 hours before using. This will yield a slightly sharper and spicier taste.
After preparing and curing homemade mustard, it’s important to store it properly. Homemade yellow mustard doesn’t have preservatives like store-bought kinds, so you will need to keep it refrigerated vs. on a shelf in your panty. The homemade mustard can be stored in the refrigerator for up to one year. It’s essential to use a tightly sealed container to maintain its freshness and flavor.