Begin by sterilising all of your tools in boiling water and try to avoid using aluminium (aluminum) or copper utensils/pots during this mustard DIY, as it can affect the taste of your final product. Stick to glass, ceramic and wood.
Powder the seeds in a spice grinder or a food processor (if it has a small jar). You could also use a mortar and pestle, but it will take a while, and a bit of an arm workout, to achieve the powdery consistency you like.
The finer the powder, the smoother the mustard will be. If you prefer it a little more chunky, then don't blend to a fine powder.
Mix the mustard powder with the rest of the spices.
In a saucepan, add the water and the spice mix. Keep the vinegar aside for now.
Cook over low heat for about 45 minutes, until it starts bubbling.
Add the vinegar and let it bubble for another 5-10 minutes. Stir occasionally as it can stick to the bottom of the pan slightly.
Pour in a glass container and leave to cool down completely before transferring to the refrigerator.
Store in an airtight jar and leave alone for at least 24 hours in the fridge. Mustard is at it's most bitter when it has just been made and requires 24 hours (at-least) to mellow out, sometimes slightly longer.
Store this in the refrigerator for around three months.
A Few Tips On How To Make Mustard:
With this recipe, I do a long slow cook, as I'm preparing milder mustard. However, for a 'hot' (as in spicy) version then it's best to use cold liquids. Whereas, for a milder, mellow yellow mustard, then you can use warmer liquids.
As a general rule, lighter seeds mean a milder taste and darker seeds mean a hotter, more bitter flavour.
As this mustard recipe uses ground seeds, it goes without saying that the amount of time spent grinding the seeds will affect the texture of your mustard recipe. If you want a thicker texture, then leave the seeds slightly coarser, for super-smooth, then blend them into as fine of a powder as you can manage.
Vinegar is used in the recipe to preserve the mustards 'zing' - Without this acid, it would mellow and lose it's tang quickly.
It's important to note that your homemade mustard will be at it's most bitter for the first 24 hours after making it. However, the bitterness will fade over time. It's good to store it in the refrigerator for a day or so while waiting for it to mellow slightly.
Adding salt to the recipe is what helps preserve the mustard (along with the vinegar). My jar is usually finished within about a month and a half, but I think this would be fine to store for three months, in an airtight container in the fridge - If not, even longer.
To turn this recipe into homemade honey mustard, then you need to add more honey. Lots of recipes call for a 1:1 ratio of honey to mustard. However, I think you can use less than this, to begin with. In fact, you can make it in a smaller batch by preparing this mustard DIY and then when you want the sweeter version, mix in a tablespoon of honey at a time until you reach your desired sweetness