The green walnut was featured as an exciting “new” import at this year's Fancy Food Show in New York. While it is a little hard to come by, the entirely edible (but really sour) green walnut is hardly new. Sixteenth century Englishmen and women were pickling and jamming them, while in the Middle East they were preserving them in aromatic sweetened syrups. It used to be that you had to cultivate a good relationship with your favorite walnut grower in order to get a special bag of the golf ball-sized, mint green orbs. A few of them finally got the hint and are now offering them for sale at select markets. Just in time to make your annual batch of liqueur de noix, or nocino.
The green walnuts this year are a little juicier and a little more plentiful than in previous years, thanks to abundant early season rains, which might explain farmers willingness to part with them at this stage. The thin outer green rind is similar to the outside edge of a watermelon. Just beneath is the proto-shell, which in July is just starting to reveal its future purpose. Below that is embryonic white pith that encloses the walnut meat, which at this point in the harvest can be anywhere from jelly-like to crumbly like fresh milk curd. They are a little hard and unyielding, but can be cut in half by carefully notching and then tapping it with a cleaver or heavy chef's knife.
The 16th century chemist George Hartman described his own method for picking green walnuts for preserves. “Take as many green Walnuts as you please, about the middle of July, try them all with a pin, if it goes easily through them they are fit for your purpose.” Please don't go around to the markets trying walnuts with a pin. For one it's unsanitary, and for another it leaves a small black blemish on the fruit. But he makes a stellar point: now is exactly the time to get them. Their inner shells are still soft and easy to prepare, whatever your purpose may be. When choosing your nuts, employ the same rules that you would for most other market fare: large dark and mushy spots are bad, nice even mint-green color is good, and they shouldn't feel hollow when you pick them up. Green walnuts do oxidize to a coffee brown when nicked, so you may see a few small dark spots on the outside. Just make sure the blemish is only on the surface and doesn't reveal a softening rot underneath.
Zack Kano, one of the K's of K & K Ranch and one of the only vendors we've found who sells green walnuts without a special request, says they will have them at all of their market stands from now until they run out of them in the fall. They have stands at the Hollywood, Torrance, Palos Verdes, El Segundo, and Westchester markets this season. “Our farmers market season ends in October, but we'll definitely have these on hand until then.”