Make it smooth, make it textured. Mild or spicy. However you like your mustard, it’s so easy to make at home for a flavorful, probiotic boosted, customizable condiment.
Before making your mustard, determine which combination of mustard seeds you want depending on preferred level of spice. Yellow mustard seeds are more mild, which brown seeds are more spicy. I like to use about 2/3 brown, 1/3 yellow seeds.
Leave the seeds whole or grind the seeds with a mortar and pestle, or spice/coffee grinder, depending on how smooth or textured you want your mustard. I like to grind just to a point where there is some fine powder, some irregular pieces, and whole seeds.
Mix in the salt and any spices you’d like, such as granulated garlic or ground cumin. If unsure which ones or how much like, start with a small amount (1/2 - 1 teaspoon or a good sprinkle) of one or two different spices, and then add additional after tasting. They provide a more complex tasting mustard, but are optional.
Add the miso paste. For every approximate cup of mustard seeds, I use about a 1/2 tablespoons worth (just by eye). This will not only provide a depth of umami flavor, but when combined with the raw apple cider vinegar, it creates some fermentation action as the mustard sits.
Now it's time to mix in the liquid. Look for about a 2:1 ratio of vinegar to water. The water just mellows out the acidity of the vinegar. However, you can use all vinegar if you like that strong vinegar flavor, or even 1:1 ratio. This is also an opportunity to adjust the level of spice of the mustard seeds. Adding cold liquid will result in a spicier mustard, while warm liquid will result in a milder mustard. Either way, look for a thickness similar to a loose pancake batter.
Place the mustard in a sealed jar and leave at room temperature for about 3 days. Check the mustard after 24 hours. If it is too thick, simply stir in a splash more vinegar.
Once finished sitting, taste. Assess the flavor. Adjust by mixing in additional spices or miso or even vinegar if you want. Keep in the fridge for several months.