Real Food Encyclopedia | Walnuts
Walnuts (of various species in the genus Juglans) are native to Asia, southeastern Europe and North and South America, and have been enjoyed since ancient times. (The nuts have been found in Iron Age archeological sites, and the ancient Greeks, Romans and Persians were known to cultivate them.) Persian walnuts (J. regia) were considered superior, and after the species was introduced to England in the 15th century, English merchants helped spread it to much of the world — the reason this species is often called the “English walnut.”
Many Native American peoples used the indigenous black walnut (J. nigra) in their cuisines, but after colonists brought the Persian walnut to North America, it began to gain prominence over its harder-to-hull cousin. According to the California Walnut Board, Franciscan monks in the late 18th century were the first to cultivate the nuts in California, now the leading state in walnut production.
Did you know?
- Unripe (green) walnuts are used to make nocino, a walnut liqueur, and are traditionally harvested on St. John’s Eve (June 23).
- The genus name Juglans is derived from the Latin “iovis glans,” or “Jupiter’s nut.”
- Most walnuts sold in their shells in the U.S. are bleached to “improve” their appearance. (Organic nuts are the exception.)
- Black walnuts in particular have been used for centuries as a traditional medicine. Said to treat parasites and constipation, black walnut extract is also used to help with fungal infections. The trees also produce a substance that is toxic to other plants — and to horses.
What to look for when buying walnuts
You are most likely to come across Persian (English) walnuts when grocery shopping. They are large, two-lobed and wrinkly, and vary in color from light beige to dark brown. These walnuts are mild in flavor with very little astringency.
Black walnuts are far less common, but many consider them superior, with more complex “walnut-y” flavor and more astringency. They are much more difficult to hull and extract from their shell — plus, they can stain. (Indeed, black walnuts have been used for centuries as a dye, including for hair.) Another North American variety you may see is the butternut (J. cinerea, also known as the white walnut).
Sustainability of walnuts
Water
Though water use is a real concern with tree nuts, walnuts have a relatively low water footprint. Still, nearly all walnuts grown commercially in the U.S. come from drought-prone California. During the severe drought in the 2010s, California walnut farmers were unable to rely on surface water and were pumping up huge amounts of groundwater, a practice that many Californians feel is poorly regulated.
Pesticides
In general, even conventionally grown walnuts show little pesticide residue on the shelled nut. However, pesticides used in non-organic walnut production are hazardous to farmworkers and to local ecosystems, so choose organic walnuts whenever possible or talk to your local walnut farmer about their growing practices.
Seasonality
Walnuts are generally harvested from August through November. Unfortunately, climate change is greatly affecting walnut trees: According to researchers at Purdue University, the trees are particularly sensitive to extreme cold and heat. The university has a breeding program in place to try to develop climate change-resistant varieties.
Geography
In temperate North America, native walnut trees are important components of a healthy deciduous forest. There are only a few commercial black walnut farms in the country; these nuts are primarily foraged, a common fall pastime (and money maker) in parts of the country. The wood of the tree is often used for timber.
In the U.S., California grows the vast majority of walnuts for consumption — primarily Persian (English) walnuts. These trees take up to seven years before they bear fruit ready for harvesting.
Eating walnuts
Storing
Store walnuts in an airtight container (like a glass canning jar with a tight-fitting lid) in the refrigerator for up to a month, or in the freezer for longer-term storage. Walnuts are particularly susceptible to rancidity, which cold temperatures will help prevent. If your walnuts smell vaguely like paint thinner, they have gone rancid and should be composted.
Cooking
Walnuts are best toasted — it gives them a deeper, nuttier, more complex flavor. In the U.S., the nuts are most commonly eaten by hand or added to baked goods and other desserts. They have a natural affinity with chocolate, maple syrup, warming spices (think cinnamon and nutmeg), bananas, lemon and vanilla.
Walnuts are also used in savory dishes around the world. Chop toasted walnuts and add them to salads or sprinkle over cooked vegetables, like green beans. They work nicely in sauces like pesto and romesco. They can also be ground and used as a thickener in stews, as in this Persian fesenjan with chicken and pomegranate. And many countries have their own versions of walnut soup.
Walnut oil is delicious in salad dressings or drizzled on vegetables. Its smoke point is low, so it doesn’t do well in high-heat applications.
Preserving
In England, pickled green walnuts are a traditional accompaniment to blue cheeses like Stilton. You can also make your own nocino, if you have access to green walnuts.
Nutrition and health
Like most nuts, walnuts contain protein. They are also high in copper and a good source of magnesium. Walnuts are rich in both omega-3 and -6 fatty acids and have been studied for their potential to lower risk of heart disease.
Top photo by Marina Lohrbach/Adobe Stock.