The following Roman mustard recipe is based on Columella (De Re Rustica 12:57:2).
Columella (De Re Rustica 12:57:2):
Semen sinapis diligenter purgato et cribrato; deinde aqua frigida eluito et, cum fuerit bene lotum, duabus horis in aqua sinito; postea tollito, et manibus expressum in mortarium novum aut bene emundatum adicito et pistillis conterito. Cum contritum fuerit, totam intritam ad medium mortarium contrahito et comprimito manu plana; deinde cum compresseris, scarifato, et, inpositis paucis carbonibus vivis, aquam nitratam suffundito, ut omnem amaritudinem eius et pallorem exsaniet. Deinde statim mortarium erigito, ut omnis umor eliquetur. Post hoc album acre acetum adicito et pistillo permisceto colatoque. Hoc ius ad rapa condienda optime facit.  Ceterum, si velis ad usum conviviorum praeparare, cum exsaniaveris sinape, nucleos pineos quam recentissimos et amylum adicito diligenterque conterito, infuso aceto. Cetera, ut supra dixi, facito. Hoc sinapi ad embamma non solum idoneo sed etiam specioso uteris; nam est candoris eximii, si sit curiose factum.
Cleanse and sift mustard-seed carefully; then wash it with cold water; and, when it has been well washed, let it lie two hours in water; afterwards take it out; and, having squeezed the water out of it with your hands, throw it into a new mortar, or into one that is made very clean, and bruise it small with pestle. When you have bruised it, draw the whole mash together to the middle of the mortar, and press it down with your flat open hand; and, after you have compressed it, scarify it; and, having placed a few live coals upon it, pour nitred water upon it, that it may free it from all its bitterness and paleness ; then raise the mortar, so that all the moisture may be drained out of it; after this put white sharp vinegar to it, and mix it thoroughly with the pestle, and strain it. This liquor does exceeding well for pickling of turnips. But, if you would prepare mustard for the use of great entertainments, when you have squeezed all the noxious juice of it, add the freshest pine-apples you can find, and almonds to it; and bruise them carefully together, and pour in vinegar upon them. So the other things as I said above. When you come to use this mustard, it will not only be very fit for sawee, but very beautiful and pleasing to the eye; for it is of an exquisite whiteness, if it be made with care.
Latin Text from V. Lundström (1902-1917), translation from A. Millar edition, 1745.