Dry mustard powder
Vinegar, white wine, or water
Mix (by degrees, by rubbing together in a mortar) the best Durham flour of mustard, with vinegar, white wine, or cold water, in which scraped horseradish has been boiled; rub it well together for at least ten minutes, till it is perfectly smooth; it will keep in a stone jar closely stopped, for a fortnight [two weeks]; only put as much into the mustard-pot as will be used in a day or two.
The ready-made mustard prepared at the oil shops is mixed with about one-fourth part salt: this is done to preserve it, if it is to be kept long; otherwise, by all means, omit it. The best way of eating salt is in substance.
The Cook’s Oracle by William Kitchiner, MD, New York, 1829
Comment: “Flour of mustard” is simply the result of grinding mustard seeds and sifting out any ungrindable bits until a fine powder is left. The resulting powder, if kept dry, will keep good indefinitely. “Made mustard” was normally made at home, although as Dr. Kitchiner notes it was beginning to be commercially available in larger cities.
As one can get a vast variety of mustards beyond the “standard” yellow goop suitable for anointing hot dogs at ball parks today, one could alter the homemade varieties to suit one’s taste or available ingredients. The prescription above is in fact four recipes, depending on whether one uses the vinegar, wine or water as a liquifying agent, and on whether the horseradish is used or omitted.