Pistachios are a type of nut which grow on pistachio trees. The shell of the pistachio is mottled beige and the meat inside is green. There are many different varieties of pistachio, also known as green almonds, but the most popular is the Kale Ghuchi or jumbo pistachio.

The pistachio tree, Pistacia vera, is native to Iran and Turkey. It is a hardy tree which thrives in the poor soil of arid and semi-arid climates. Left to its own devices, Pistacia vera can grow upwards of 6m (20ft) and can survive until the climate becomes humid.

Pistachios grow in clusters, like grapes, and when they ripen the shells split open at one end. One theory holds that, if you stand with your lover under a pistachio tree in the moonlight and listen to the ripening nuts crack open, then you will have good luck. Another theory holds that, if you are in a position to be standing with your lover under a pistachio tree in the moonlight listening to the ripening nuts crack open, then you already have good luck.

The light brown shell is usually slightly open when the nut is a brilliant green colour, and ripe. The shell protects the oil-rich (around 50% oil) fruit, which is encased in a brown or mauve seed coat, and has natural antioxidant properties.

Pistachios are harvested by being knocked from the tree onto tarpaulins and gathered up. The shells are then often dyed, as the natural colour looks dirty to some people. The shells are either bleached until they are almost white, or they are dyed bright red. White pistachios and red pistachios are, however, the same type of nut.

Most pistachios in the world today are grown in Iran, Turkey, Syria, Lebanon, and California, USA, where the trees were introduced by a Frenchman in the late 19th Century. Most pistachios in the world today are consumed in the USA.

Culinary Uses

Pistachio kernels are used as a seasoning for meat, and sausage products, or as flavouring in chocolate confectionery, bakery products and ice cream.

They are also sold roasted, and salted in their shells for consumption as a snack food, and are also used as a raw material for pistachio nut oil.

Roasted and Salted

The roasted nuts usually come in packets or tins, having been picked, processed, and then sent to the packaging factory. If you live in Europe the pistachios are likely to be Iranian nuts packaged in an Italian factory¹.

Pistachios are not in their natural state when you buy them roasted and salted. In Iran, for example, there are 5 industrial plants that salt, and then roast, and export more than 150,000 tonnes of pistachios a year. The second largest exporter is the US (California), which is likely to overtake Iran in 2010 as trade sanctions are continuing to affect the industry because of Iran's nuclear energy programme, as well as under-investment in agriculture, and packaging technology.

Roasting is done in a continuous process after the nuts have been cleaned, graded and passed through a saline solution, using sea salt, to make them slightly salty. After saline immersion the nuts are shaken to remove any excess liquid entering the open shell. A typical machine can process 1000kg of nuts per hour and consume 20kW of energy.

The Health Benefits

Epidemiological and clinical studies have revealed that nuts generally, including pistachios, provide some or all of the following benefits:

• Eating nuts reduces the incidence of coronary heart disease. They can reduce cholesterol and provide additional protection because of high levels of omega-3 fatty acids and low levels of saturated fats.

• Nuts have a low glycemic index (GI), which protects against some types of insulin resistance problems (diabetes). A lower GI² suggests slower rates of digestion and absorption of the foods' carbohydrates. Recent studies have shown that the consumption of an alcoholic drink prior to a meal reduces the GI of the meal by approximately 15%. This might explain why the combination of nuts and alcohol is so popular! On the other hand, too much salt and alcohol can raise blood pressure, and lead to vascular diseases (stroke or heart attack).

• Nuts supply one of the best natural sources of vitamins E and B2 (riboflavin, an antioxidant), and are rich in protein, folate, fibre, and essential minerals such as magnesium, phosphorus, potassium, copper, and selenium.

• The Pistachio Principle describes methods of "fooling" one's body into eating less. The physical activity of shelling and eating pistachios, one-by-one³ slows the rate of consumption allowing the body to feel sated before over-consumption.

Enjoying Pistachios

Buy a bag or tin of pistachios, red or white, salted or unsalted. If you can, choose pistachios that are still in the shell, or you will be deprived of a major part of the pleasure of eating them. Select a nut whose shell is split open at one end (most of them should be). Remove and discard the shell. Pop the meat of the nut into your mouth. Chew and savour.

Or, buy a tub of pistachio ice cream. Indulge.