Funnily, though, various individuals on the Internet offer all kinds of remedies (all of which turn out to be totally false) for eliminating instantly the black stains. Common suggestions are bleach (a solution of sodium hypochlorite or hydrogen peroxide) and lemon juice. Somebody said that common cooking oils would get rid of the stains, and there was even a woman who said that the miracle product was toothpaste.
Now, why have I been gathering green walnuts? Well, as I explained in a blog post two months ago [display], I'm experimenting with a Greek Cypriot recipe for fresh walnuts preserved in sweet syrup. The precise description of this product (both in English and in French) is quite complicated, as I would have to mention the fact that the walnuts were picked when they were green and soft, whereas they soon turn black, and that the preservation process involves lots of boiling in syrup. Then I should maybe explain that the little brown blobs floating around in the dark syrup between the black walnuts are roasted almonds and cloves. For the moment, I think I'll refer to this product, from now on, simply as sweet walnuts (noix sucrées in French).
I'm currently preparing a second batch. Ten days ago, the walnuts in the first experimental batch were smaller and softer, and I spiked them first and started to soak them in the sun before peeling them.
From that point on, the processing consisted of boiling the walnuts, many times, in a dense solution of sugar, with a little lemon juice. I also assembled a few extra ingredients: almonds, cinnamon and cloves.