Homemade grainy mustard

Every year my SO and I send out homemade holiday presents to our families. Our two most requested presents are our fruitcake and our mustard, and since we've made these recipes for nearly 10 years now, we figure it's time to share. I'll be posting the mustard today, followed followed by the fruitcake recipe in a few weeks (once we've had time to experiment some with the recipe).

Our mustard is made from whole yellow and brown mustard seeds that have been only partially crushed, and thus you get treated to little bursts of mustard flavor as you eat. The flavor is different from store-bought mustards: our mustard is sharper than most, doesn't taste as much of vinegar or turmeric, and has a hint of onions thanks to shallots. We have reports from family members that even though they've tried, they can't find anything like this in stores. Since we just got finished making our annual batch of mustard a few days ago¹, it's this week's end-of-the-week recipe blogging post.

Note that this recipe requires a few days to soak the mustard seeds before making, and tastes best if left to mellow for a week or two before eating, so plan accordingly.

1/2 cup dry yellow mustard seeds
1/2 cup dry brown mustard seeds
1 cup rice vinegar
1 shallot, finely chopped
1 tablespoon kosher salt

1. Put the brown and yellow mustard seeds into separate containers and add approximately 3/8 cup (1/4 cup plus 2 tablespoons) of rice vinegar to each container. Cover each container tightly and let sit at room temperature for at least 2 days, stirring occasionally. If the mustard seeds end up looking dry during the soaking period, add a bit more vinegar to moisten.
2. Grind each type of mustard seed until many of the seeds have broken open (the seeds should start clumping together, and you'll start to see little bits of seeds in addition to whole seeds). For an artisanal feel, you can do this by hand with a mortar and pestle; it's a lot of hard work, and is guaranteed to make your grinding arm sore. For the lazy cook's mustard, put the seeds into a food processor and process with long pulses. It's best to grind the two types of seeds separately, as the yellow and brown mustard seeds grind at different rates.
3. Mix the mustard seeds, salt, shallot, and remaining vinegar (~1/4 cup) in a bowl. Add extra vinegar to bring the mustard to a nice paste-like consistency (it may take an extra tablespoon or so).
4. Transfer to jars and store in the fridge.

Notes:

Don't use aluminum cookware with this recipe, as it may react with the vinegar.

There's no need to use exactly 1/2 cup of each type of mustard seed; as long as you have a total of one cup of seeds you should be fine. The yellow seeds are milder than the brown seeds, so variations in proportions will change the sharpness of the final product.

We store the mustard in sealed jars in the fridge, though it may not require refrigeration (and we regularly ship it cross country without issue). The mustard keeps for a long time; we've kept jars in the fridge for more than a year and it still tastes great.

The recipe above makes a bit less than 2 cups of finished mustard. We typically make at least five times that amount (2 1/2 cups of each type of seed, ~2 cups of vinegar to soak each type of seed initially, 5 tablespoons kosher salt, 5 shallots, and 1 to 1 1/2 cups vinegar for mixing at the end), and as long as you're using a food processor for grinding you won't go crazy. In the past we've always hand-ground small batches of mustard; we only recently started using a food processor due to making large batches, and thus we're not sure how well a food processor will work with a small batch of mustard.

This recipe is based on one in Walden (1995), a book which wins the Radagast and SO award for best food photography.

Reference:

Walden, H. 1995. Sensational Preserves: 250 recipes for jams, jellies, chutneys, and sauces. Reader's Digest, NY.

¹ And yes, this means that if you're a family member waiting for your holiday mustard shipment, your mustard is indeed in the mail.