They are usually picked before the shell forms and hardens on the nut — i.e., unripe walnuts, aka Green Walnuts. The whole nut is used, including this unripe, soft shell.
They are an acquired taste. Some people don’t even like the texture.
To make Pickled Walnuts, you prick the walnuts all over with a needle, tines of a fork or a thin skewer. You then brine the nuts, changing the brine every day for the first three days, and covering with something like a plate to keep them down into the brine, then allowing them to stand for another 3 to 6 days in a fresh brine solution, then drain them and let stand in the sun for 3 days until they blacken.
You then pack them into jars, and cover them completely with a heated solution made from vinegar, sugar and spices. They need 30 to 60 days before eating.
Some methods omit the drying process, and boil them instead several times.
Pickled Walnuts are made throughout Europe, from England down to Italy. The type of vinegar to pickle them with will vary by country.
Note: Opies brand lists salt as an ingredient, but does not show sodium value in nutritional information.
1 x 390 g (14 oz) jar, drained of liquid = 190 g (6.7 oz) of actual pickled walnut product (Opies brand)
Literature & Lore
“Everyone ate pickled bloomin’ walnuts then. Don’t ask me why. I think perhaps because they were a lively spicy taste and there was no Chinese or Indian food then! Most of what we ate by modern standards was really very plain, even dull.” — Jackman, Nancy. With Tom Quinn. The Cook’s Tale. London: Hodder & Stoughton. 2012. Page 124.