Walnut shells once cleaned Army aircraft parts, until one grounded a helicopter
Ground walnut shells made a cheap, gentle grit for blasting grime off United States Army aviation parts. Then investigators of a fatal Chinook crash in Mannheim on 11 September 1982 found that shell grit had blocked an oil port, and the Army stopped using it. The nut's afterlife extends far beyond the kitchen.
Botanically a walnut is not a true drupe. Its green outer husk develops from an involucre, not the carpel, making the fruit an accessory, drupe-like nut. Inside the husk sits a hard wrinkled shell, usually in two halves, and within it the oily kernel wrapped in a brown seed coat whose antioxidants slow rancidity. The husks stain hands and can irritate skin, partly because of juglone, which reaches 2 to 4 percent of their fresh weight. The trees leaf out late, well past the middle of spring.
The Persian or English walnut, Juglans regia, originated in Iran and underlies nearly all commercial cultivars; black walnuts and heartnuts are also grown. Byzantines and Ottomans called it the royal nut, and a twelfth-century agricultural book by Ibn al-Awwam covered its cultivation in Iberia. The wal in the English name is a Germanic root meaning foreign, the same one behind Wales and Wallachia. World output reached four million tonnes in shell in 2023, 35 percent of it from China.
Kernels are about 65 percent fat, and unusually for nuts most of it is polyunsaturated. Storage matters: warmth and humidity above about 70 percent invite moulds that produce aflatoxin, a potent carcinogen. Cooks use walnuts in baklava, Circassian chicken, Georgian satsivi, Slovenian potica and Bulgarian tarator soup, and steep green walnuts to make the liqueur nocino.
The husks yield a durable brown ink thought to have been used by Leonardo da Vinci and Rembrandt, and Romans dyed hair with them. Crushed shells still filter oil from water in the petroleum industry and go into cat litter. In China, large symmetrical wenwan walnuts are carved, rolled in the hand and collected as status symbols, and people even gamble on pairs sold unopened in their husks.
Source: Walnut
