You can pick walnuts when they are green, but this early harvest is not for obtaining the hard-shelled nut meat. Harvesting walnuts at this stage means gathering the entire fruit—the soft, green outer hull and the unformed nut inside—before the inner shell has hardened. This unripe fruit is primarily used in traditional culinary preparations due to its high concentration of tannins and potent compounds.
Identifying the Ideal Green Harvest Window
The perfect timing for picking green walnuts is highly specific and depends entirely on the physical development of the shell. This window typically occurs in early to mid-summer, often around the middle of June, depending on the climate and location. The traditional harvest date in Europe for making the liqueur Nocino is often cited as the Summer Solstice, June 24th, which serves as a good guideline.
The most reliable way to determine readiness is by using the “pin test” or “needle test.” A slender needle or skewer should pass easily all the way through the entire fruit—the outer hull and the embryonic nut—without meeting any resistance. If you feel a hard, developing shell, the harvest window has closed, and the fruit is no longer suitable for preparations requiring the soft, whole fruit. Ready-to-pick green walnuts should appear smooth, plump, and uniformly green.
Specialized Culinary Uses for Unripe Walnuts
The primary reason to harvest walnuts when they are green is to utilize the intense, complex flavor profile locked within the soft hull and underdeveloped nut meat. These unripe fruits are too bitter to eat raw, but the tannins and aromatic oils transform through specific preservation methods. The two most prominent culinary uses are the Italian liqueur Nocino and traditional pickled walnuts.
Nocino is a dark, complex digestif, a liqueur traditionally made by steeping whole, quartered green walnuts in high-proof neutral alcohol, often for many months. The tannins and aromatic compounds from the fruit’s hull are slowly extracted, imparting a deep, earthy, slightly spicy flavor and a striking black-brown color to the spirit.
Pickled walnuts, a classic English preparation, require the fruit to be harvested before the inner shell forms. In this method, the whole green walnuts are typically brined, often for a week or more, and then boiled and preserved in a spiced vinegar mixture. The soaking and cooking processes are necessary to leach out bitterness and transform the texture of the fruit. The resulting pickle is a dark, pungent, and savory condiment, where the entire fruit, including the hull, is edible.
Essential Handling and Processing Precautions
Handling green walnuts requires specific precautions due to the high concentration of juglone, a natural defense compound found throughout the walnut tree. When the green hull is cut or bruised, the precursor chemical rapidly oxidizes into juglone, a powerful natural dye. This compound causes severe, long-lasting brown-black stains on skin, clothing, and any porous surface it touches.
Wearing heavy-duty gloves is mandatory during the entire harvesting and processing stage to prevent the juglone from staining your hands for several weeks. Beyond staining, juglone can also act as a skin irritant for some people, causing itching or blistering. The initial preparation of green walnuts for both pickling and Nocino often involves piercing the entire fruit multiple times with a skewer or knife. This step is necessary to allow the tannins and bitterness to leach out during the initial soaking or steeping phase. Many recipes also call for an initial soaking period in water, sometimes with daily water changes, to reduce the initial bitterness before further preservation.