Part of my fall ritual includes drying the herbs and spices that grow in my garden. This year, for example, I have already dried wild carrot flowers and greens, lemon balm, camomile, purple clover, basil, oregano, chives, and I still have a fair amount to do, including rosemary, mint, and rosehips. This past Saturday, as I was considering what still had to be done, I noticed the purple shiso, which grows wild in my garden and which I only just learned is edible this past summer. I had heard that both the leaves and the seeds could be dried and kept as spices, and I was fairly confident that I could dry the leaves without much problem, I was not sure how to go about harvesting the seeds. I had no idea when they were mature, no idea how they should be extracted from their husks, no idea whether they should be dried before or after they were extracted, no idea, in short, at all.
The internet told me nothing very useful, so I decided that some experimentation was in order. I stripped the seed pods from a few stems and tried rubbing them between my palms to remove the husks. This operation was somewhat less effective than I hoped. The husks could eventually be removed, but the moisture made them cling to the seeds, and the seeds cling to each other. I noticed, however, that the seeds from the pods at the very tip were white and soft, while those nearer the bottom were brown and harder and tasted quite strongly when bitten. Whether or not these lower seeds were mature enough to be fertile, they were certainly mature enough for my purposes, so I cut the whole plant. I stripped the leaves into one colander and the seed pods into another, rinsed them both, and left them to dry over night. I then dried them as I dry everything else, turning my oven to its lowest heat, putting a large cookie pan on the lowest rack to block the direct heat from the element, placing the herbs in a second cookie sheet on a higher rack, and leaving the oven door ajar to allow the moisture to escape.
The leaves dried easily, as I expected they would. Though they are larger than basil or mint leaves, they are of a similar thickness and texture, and they dry much the same. The seeds also seemed to dry well, but they were still in their husks, and I was still faced with the question of whether I could extract them. I rubbed a few between my palms again, and the husks broke up quite easily, but the seeds still clung together in their little clusters. By rubbing more vigorously, I was able to separate the seeds, but I was left with a handful of chaff mixed with the seeds that I wanted. I tried sifting this mixture through several sizes of colandar and sifter, but anything large enough to let the chaff through let the seeds through also. I tried picking the seeds out of the chaf by hand, but gave this up as too tedious after a single seed. In the end, I was reduced to putting the seeds and chaf together in a small mixing bowl and shaking it gently until the heavier seeds gathered on top of the lighter chaff. I would then tap out the gathered seeds into a second bowl, repeating the process until I had removed as many of the seeds as my patience would allow.
There are probably more efficient ways to dry purple shiso seeds, and I would appreciate anyone who could offer advise on how to make the process simpler, but I am quite satisfied with the end product of my experiment. The seeds do seem well dried, and they have certainly retained their flavour. Now I just need to learn how to cook with them.