Real Food Encyclopedia | Walnuts

Walnuts (of different species) are native to eastern Asia, southern Europe and North and South America. The nuts have been found in Iron Age archeological sites in Europe. The ancient Greeks, Romans and Persians cultivated walnuts. Persian varietals were considered superior in taste, size and oil content. The Persian walnut made its way to China by 400 AD, and was introduced to England in the 15th century, although cultivation of the nut never really took off in England. English merchants helped spread the nut to much of the rest of the world, though, and the name “English” walnut stuck.

Many Native American tribes used the indigenous black walnut in their cuisines (the Apache were apparently especially fond of the nuts, mixing it into pemmican and eating the nuts fresh). Early New England settlers brought the Persian walnut to North America, where it gained prominence over the harder-to-hull black walnut. According to the California Walnut Board, Franciscan monks were the first to cultivate the nuts in California in the 1700s. The first commercial plantings of the nut in California weren’t until 1867.

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Fun Facts about Walnuts:

  • Apparently, cracking walnuts with one’s head is a thing.
  • Unripe, green walnuts are used to make nocino, a walnut liqueur traditionally harvested on St. John’s eve, June 23rd.
  • Walnuts’ genus name, Juglans, is derived from the Latin iovis glans, or “Jupiter’s nut.” (Jupiter is the Roman equivalent of the Greek god Zeus.)
  • Walnuts were thrown at Roman weddings as a symbol of fertility.
  • Luther Burbank, he of the famous Russet-Burbank (aka “Idaho”) potato, is credited with developing improved California walnut cultivars.
  • Most walnuts sold in their shells in the US are bleached to “improve” their appearance. (Organic nuts are the exception.)
  • Black walnut trees produce a substance that is toxic to other plants and the tree is also toxic to horses.

What to Look for When Buying Walnuts

By far, you are most likely to come across English walnuts at the market. They are large, two-lobed and wrinkly like a brain, and vary in color from light beige to dark brown. English walnuts are mild in flavor with very little astringency.

Black walnuts are far less common, but are said to be far superior in flavor than English, with more complex “walnut-y” flavor and more astringency. They are much harder to hull and extract from their shell — plus they stain something fierce. (Indeed, black walnuts have been used for centuries as a stain and a dye. You can make your own black walnut dye if you’re the industrious type.) Hank Shaw over at Hunter, Angler, Gardener, Cook has a great post on foraging, hulling, shelling and extracting black walnuts — sounds positively exhausting, but worth it.

Sustainability of Walnuts

A real concern with commercial walnuts has to do with the trees’ use of water. California walnuts, which make up around 99 percent of all commercial walnuts grown in the US, require a significant amount of water. In drought-prone California, this is especially concerning. During the recent major drought, California walnut farmers were unable to rely on surface water and were pumping up huge amounts of ground water, a practice that many Californians feel is poorly regulated.

Unfortunately, it’s also looking as though climate change will greatly affect walnut trees in particular. According to researchers at Perdue University, the trees are particularly sensitive to extreme cold and heat, both hallmarks of climate change-related weather events. The university has a breeding program in place to try to develop climate-change resistant varieties of the trees.

Pesticides and Walnuts

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 ecology, so choose organic walnuts whenever possible or talk to your local walnut farmer about his/her growing practices.

Walnuts Seasonality and Geography

Walnuts are generally harvested from August through November. Here is a great photo essay of a walnut harvest in California.

Walnuts and Cultivation

By far the most common type of walnut used in the kitchen is the English (or Persian) walnut (Juglans regia). Other types of walnuts include the North American black walnut and the North American butternut (also known as the white walnut). In temperate North America, walnuts are important components of a healthy deciduous forest. Walnut fruit is green and fleshy and surrounds the walnut seed. English walnut trees take up to seven years before they bear fruit ready for harvesting.

Black walnuts are primarily foraged. There are only a few commercial black walnut farms in the US. Black walnut foraging is a common fall pastime (and money maker) in parts of the United States. California grows the vast majority of English walnuts in the US. China, Iran, the US and Turkey are the top global producers.

How to Cook Walnuts

Storing Fresh Walnuts

Store walnuts in an airtight container (like glass canning jars with tight fitting lids) in the refrigerator for up to a month, or in the freezer for longer-term storage. Walnuts are particularly susceptible to rancidity, but cold temperatures help keep all nuts from going rancid. If your walnuts smell vaguely like paint thinner, they have gone rancid and should be composted.

Cooking With Walnuts

Walnuts are great additions to both savory and sweet dishes. In the US, the nuts are most commonly eaten out of 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 best toasted — toasting any nut makes them nuttier and crisper, with a deeper, more complex flavor. Aside from their more familiar addition to sweets, walnuts are used extensively around the world in savory dishes. Chop toasted walnuts and add them to salads and as a topping for cooked vegetables like green beans. You can substitute walnuts for pine nuts in traditional basil pesto or kale pesto.

In Persian cuisine, walnuts are used extensively in savory dishes, ground and used as a thickener in stews, like this pomegranate and duck khoresh. In Italy, walnuts are ground and used as a sauce for pasta. The nuts are also made into soup — the French make a cream of walnut soup, the Chinese a walnut soup with rice flour and the Turks and Balkans a walnut soup with yogurt.

Walnut oil is pressed from the seeds and makes a delicious salad oil (its smoke point is low, so it doesn’t do well in high-heat applications) or for drizzling on vegetables.

Preserving Walnuts

In England, pickled walnuts are a traditional accompaniment to blue cheeses (like Stilton), made from unripe (green) walnuts. You can also make your own nocino, if you have access to green walnuts.

Walnuts Nutrition

Walnuts are a wonder food. Like most nuts, they are high in protein and fiber. They’re also loaded with nutrients, like Vitamin B6, folate, thiamin, iron, magnesium, copper and manganese. Walnuts are a great source of both omega-3 and -6 fatty acids, essential fats that the body needs to build brain and nerve cells. They also may lower the risk of heart disease. 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. Black walnuts are also used as a natural hair dye.