Homemade Fermented Mustard

1 1/3 cup apple cider vinegar I use the Bragg's with the "mother" in it.
1 1/3 cup mustard seeds (I like 50/50 yellow and brown) remember the darker the seed the spicier it is
2 teaspoons kosher salt, or to taste I use the kind without iodine
1-2 tablespoon brown sugar (optional)
Honey (optional, for honey mustard)

In a large bowl or jar (a wide mouth quart jar works perfectly) combine the first three ingredients. Cover and set aside at least 24 hours.

The next day, the mustard seeds will have absorbed most of the liquid. Add sugar and salt and blend in a blender or food processor until creamy, 1-2 minutes.  As with most things I make I used my magic bullet to process it. If you prefer it chunkier like I do then put aside half of the soaked overnight seeds then add them back in after blending the rest.    

Store in a glass jar, I've noticed if I store it in anything else the mustard will pick up off flavors from the containers.

If you taste the mustard at this point, it will be quite vinegar-y and sharp; for the best flavor, cover the jar again and let set at room temperature for another 24-72 hours. When the flavor is what you like, refrigerate the mustard and use within 3 months, makes a pint.

Adapted from America’s Test Kitchen, this is a great recipe to play around with the flavors. Use a different vinegar (I’m planning to try red wine vinegar soon, and imagine malt or champagne vinegar would also be interesting), or try another liquid to replace the cider (apple juice for a non-alcoholic version, but I’m also curious to try a dark beer or even something like bourbon). As long as you maintain the proportion of liquid to mustard seeds (2 parts vinegar, 2 parts mustard seeds, 1 part additional liquid), the possibilities are completely up to you.

At this point you can add other flavorings such as garlic, or honey.