Walnut

A walnut is a seed from a tree.

It grows inside a green skin called a husk. As the nut grows, the husk gets soft. The shell inside becomes hard.

The hard shell protects the food inside. This food is called the kernel. The kernel is often in two halves. A thin brown skin covers the kernel. This skin helps keep the oil fresh.

You can eat the kernel. People use them in cakes and pies. Some people even use the shells for cat litter. Walnuts are a tasty treat!

A walnut is a seed from a tree.

Most walnuts come from the Persian walnut tree. These trees grow leaves late in the spring.

Walnuts grow inside a green outer layer called a husk. As the nut ripens, the husk becomes brittle. Inside the husk, the shell becomes hard. This shell protects the kernel, which is the part we eat.

The kernel is often in two halves. A thin brown skin covers the meat. This skin has antioxidants. Antioxidants are parts that help keep the oil from going bad.

People use walnuts in many ways. You can eat them in cakes, pies, or salads.

Some people even use crushed shells to make cat litter. This is a way to use a waste product.

Be careful, though. Some people have allergies to walnuts. This can make it hard to breathe or cause stomach pain. If someone has a bad reaction, they may need medicine right away.

A walnut is the edible seed of a tree from the genus Juglans.

Most people eat the Persian or English walnut, which is known as Juglans regia. These trees are special because they are late to grow leaves. They usually do not grow leaves until halfway through the spring. The walnut is considered an accessory fruit. This means the outer covering is not part of the fruit's main structure. Instead, it is a drupe-like nut.

Many people enjoy them because they are full of energy and nutrients.

Walnuts grow in a very specific way. First, the seed is enclosed in a green husk. As the fruit ripens between September and November, the husk becomes brittle. Inside that husk, the brown shell becomes hard to protect the seed. This shell often has two segments, but it can have three or four.

Inside the shell is the kernel, or the meat. A thin brown seed coat covers the kernel. This coat contains antioxidants. These help protect the oil-rich seed from oxygen so it does not go bad.

People have known about walnuts for a very long time. During the Byzantine era, people called the walnut the "royal nut." In the 12th century, Ibn al-'Awwam wrote about growing them in the Iberian Peninsula. The name "walnut" even has a history in language. The "wal" part of the name comes from Germanic words. It meant something that was foreign. This same root appears in many German, Dutch, and Swedish words for the nut.

There are many different kinds of walnut trees around the world. The Persian walnut comes from Iran. The black walnut is native to eastern North America. There is also the Japanese walnut, which people call a heartnut.

In 2023, the world produced four million tonnes of walnuts in their shells. China produced 35% of that total amount. The United States, Iran, and Turkey are also big producers. Nutritiously, English walnuts are 65% fat and 15% protein. They are also very high in manganese.

Walnuts are useful for much more than just eating. You can use them in brownies, cakes, or even walnut soup. Some people even use ground shells to make cat litter. This is a good way to use a waste product. Artists have even used the husks to make brown ink.

However, you must be careful if you have an allergy. About 0.4% of people in Europe and the US have a walnut allergy. For some, this can be very serious and require medicine.

A walnut is the edible seed produced by trees within the genus *Juglans*. These trees belong to the family Juglandaceae. Most people recognize the Persian or English walnut, scientifically named *Juglans regia*. While often called a nut, the walnut is technically an accessory fruit. This means the outer covering, called an involucre, is not morphologically part of the carpel. Because of this structure, it is described as a drupe-like nut rather than a true drupe.

The growth and ripening of a walnut follow a specific biological sequence. In the northern hemisphere, walnuts typically ripen between September and November. Initially, the seed is enclosed in a green husk. As the ripening process continues, the husk becomes brittle and the inner shell hardens. This shell protects the kernel, or meat, which usually consists of two halves separated by a thin partition.

The seed kernels are covered by a brown seed coat. This coat contains antioxidants that protect the oil-rich seed from atmospheric oxygen. This chemical protection prevents the oils from undergoing rancidity.

There are several distinct species of walnut trees used for food production. The Persian walnut (*J. regia*) originated in Iran and is the most common commercial variety. The black walnut (*J. nigra*) is native to eastern North America. Another variety is the Japanese walnut, also known as the heartnut (*J. ailantifolia*). Other species include the California black walnut (*J. californica*), which is often used as rootstock for commercial propagation. There are also butternuts (*J. cinerea*) and the Arizona walnut (*J. major*).

Walnuts have a deep history in human culture and language. During the Byzantine era, the walnut was known as the "royal nut." In the 12th century, Ibn al-'Awwam documented walnut cultivation in the Iberian Peninsula. The word "walnut" itself contains a Germanic element, "wal," which means foreign. This root is found in many other Germanic languages, including German, Dutch, Danish, and Swedish.

Global walnut production is a significant industry. In 2023, the world produced four million tonnes of walnuts in the shell. China was the largest producer, contributing 35% of the total harvest. Other major producers included the United States, Iran, and Turkey.

Nutritially, English walnuts are quite dense. They consist of 65% fat, 15% protein, and 14% carbohydrates. They are especially high in manganese, providing 148% of the Daily Value (DV) in a reference amount. Unlike many other nuts, walnut oil is largely composed of polyunsaturated fatty acids. Specifically, it contains 72% polyunsaturated fats, including 58% linoleic acid and 14% alpha-linolenic acid.

Walnuts have many diverse uses beyond human nutrition. The husks contain phytochemicals like polyphenols that can stain skin or be used as brown dyes. Historically, artists like Leonardo da Vinci and Rembrandt may have used husk pigments for ink. In industry, crushed shells are used for low-abrasive cleaning and blasting. Some companies even manufacture cat litter from ground walnut shells.

However, improper storage can be dangerous. If humidity levels rise above 75%, fungal moulds can form. These moulds release aflatoxin, which is a potent carcinogen. Any batch containing mold-infested walnuts must be entirely discarded.

While walnuts are healthy, they can cause serious allergic reactions in some people. Lifetime walnut allergies affect about 0.4% of the population in Europe and the United States. In American children, the prevalence of nut allergies can reach as high as 5%. Reactions can cause symptoms like abdominal pain, difficulty swallowing, or even fatal anaphylaxis.

Because of these risks, walnuts are considered a priority food allergen in Canada. Managing these risks is important for both food safety and public health.