It was all a bit of a disaster. I got over-paranoid about whether the seeds were toxic, and the seedpods were too small and few to make more than a pinch of mustard from anyway. Then to top it off, someone knocked the drying seedpods off the windowsill and the tiny seeds spilled and vanished.
Anyway, now that I know what wild turnip REALLY is, I'm trying again.
I was inspired to make wild mustard after reading Euell Gibbons' 1962 foragers' classic - Stalking the Wild Asparagus.
Gibbons lived in the United States and wrote about making mustard from the seeds of Brassica nigra:
----------------------- [The seedpods] ripen unevenly, and as soon as they are ripe, split open and the seeds drop out.
The best way I have found to collect these seeds is to gather the whole seedstalk ... just when the lower pods are beginning to shatter, and spread them on one of the large plastic sheets, which I have found such a handy help in foraging.
After drying out in the sun for a few days, they will be ready to thresh out by beating them with a flail. From one 9 by 12 sheet piled full of ripening seed stalks, I have winnowed out 1/2 gallon of clean mustard seed, and that is as many as I can possibly use in a year.
The clean dry seeds can be ground ... this will give you the same kind of dry mustard you can see on the spice shelves at your grocers, and it can be used in any recipe that calls for dry mustard.
To make the yellow pasty condiment that is called Prepared Mustard, put some flour in a pan and toast it in the oven, stirring occasionally until it is evenly browned ...
Mix this browned flour, half and half with ground mustard and moisten with a mixture of half vinegar and half water until it is the right consistency, and your condiment is ready to use. -----------------------
In a New Zealand context, wild turnip might be one of the best plants to make mustard from.
The wild turnip round our house is covered in seed pods at the moment ... My son and I picked some bunches: And they've been drying for a few days now. They've almost all dried and split and released their seeds. (I've tried a nibble of the seeds, and they're nice.) Hopefully we'll be making mustard in a day or two - although not in such bulk quantities as Euell Gibbons!