Walnuts

Walnuts carry more alpha-linolenic acid, the plant form of omega-3, than any other commonly eaten nut, and that single fact drives most of the research interest. Trials looking at walnut-enriched diets have generally examined blood lipids, where the consistent finding is a modest reduction in LDL cholesterol, and the effect appears to come from the fat profile rather than from anything exotic.

They are also unusually high in polyphenols for a nut, concentrated in the skin, which is the same place the bitterness lives. Removing the skin removes some of that.

Research on cognition is the area most often oversold. There are observational studies associating regular nut intake with better measured cognitive performance in older adults, and some short trials on walnuts specifically, but the results are mixed and the designs are small. The honest summary is that walnuts are a nutritionally dense food with a good fat profile, and that the brain claims run ahead of the evidence.

They are calorie dense, roughly 650 calories per 100g, which is worth knowing when a tradition tells you to eat them by the handful.

Walnuts spread east out of Persia and Central Asia along the same trade routes that moved everything else, which is why the Chinese name, hu tao, carries the character hu, historically used for things arriving from the western regions. They reached China by the Han period and were established in Kashmir early enough that Kashmiri cooking treats them as local rather than imported.

Kashmir is still where the Indian subcontinent's walnuts come from, and akhrot chutney, ground with chilli and yogurt, is a Kashmiri Pandit staple that appears on the wazwan table and at home. In China the kernel became both a food and a medicine, eaten candied at new year and ground into hu tao hu, a sweet walnut soup served warm in winter.

In Korea, hodu-gwaja, the walnut-shaped cake from Cheonan, is the country's best-known train-station snack, and it contains an actual walnut piece inside the red bean filling.

In Chinese cooking walnuts are candied and fried for walnut shrimp, ground with rice into the sweet soup hu tao hu, and tossed into stir fries where the bitterness plays against soy and sugar. Northern cooking pairs them with dates and goji in tonic soups.

In Kashmiri cooking they are ground raw into chutney with green chilli, yogurt and salt, which is the sharpest use of the tannin in the whole repertoire, and they turn up crushed in festival sweets with jaggery.

Korean baking uses them in hodu-gwaja, and Japanese kitchens grind them into kurumi dare, a walnut dipping sauce for chilled noodles and dango that behaves like a richer sesame sauce.

Raw, they go into salads and rice dishes for texture. Toasted, they get sweeter and lose some bite. Candied, they stop being a nut and start being a sweet.

Toast them in a dry pan or a low oven for a few minutes until they smell sweet. They burn faster than almonds because of the oil content, so watch them rather than timing them.

To remove the bitterness, blanch the kernels in boiling water for a minute, then rub them in a clean towel while warm and the papery skin comes away. This matters for delicate desserts and matters much less in a chutney where you want the tannin.

For the Ayurvedic use, soak overnight and peel in the morning, which softens them and is said to make them easier to digest.

Store them cold. Walnuts go rancid faster than almost any other nut, and rancid walnuts taste sharply of paint. The freezer is the right place, and they keep there for the better part of a year. If a bag tastes bitter in a way that stings rather than dries the mouth, it has turned.