To make up for my longer absence over the weekend, here is a second post. Last autumn, I collected sloes to try out a few recipes. One of them was for a mustard from the Oeconomia ruralis et domestica:

However, there are many species and types of plums and there are cerasa, cherries, that you would also like to count among the plums propter similitudinem (on account of their similarity), there are pruna sylvestria, sloes, Virgilius calls the bushes on which they grow spinos. Schleedorn (spiny sloes) are a good thing if you use them properly because you make sloe wine from them.
In many places, they also preserve them around Michaelmas after the frost has struck them and they have turned soft. You take mustard and grind it with vinegar, and when it has been ground very fine, you put the ground mustard into a new pot and add the sloes whole. Let it stand thus for fourteen days, and then when you eat dried meat, fried pickled herring, ham, or other things from which you usually get scurvy, eat it along with them from a small condiment bowl (Commentichen). This helps, next God, that scurvy will leave you alone and it is good to eat.

Last weekend, I met with friends from my medieval club and we opened one of the jars to try what it had become. As an initial experiment, this was just a basic combination of sloes, mustard powder, and white wine vinegar with a pinch of salt. After a few months in the jar, it turned purplish and more liquid, but neither fermented nor went mouldy. I expected the result to be sharp and sour, but it was surprisingly mellow and pleasantly fruity. It still stung on the tongue and was best used in small quantities, but this is a recipe with surprising depth and possibilities. I will try to find the time to develop it some more the coming year, both in terms of the base – different vinegars, dark or light mustard – and maybe spices. None of this is mentioned, but all of it could well go unsaid as a matter of course, or left open to the reader.
The alleged antiscorbutic properties may actually be real. Scurvy is an effect of vitamin-C deficiency, and sloes contain vitamin C. This is destroyed very effectively by cooking, but much less by pickling. The vitamin-C content in the finished mustard may be significant enough to make a difference at a time of the year when fresh fruit and vegetables were rare.