The pistachio (Pistacia vera L., Anacardiaceae or sometimes Pistaciaceae) is a small tree native to mountainous regions of Iran, Turkmenistan and western Afghanistan, that produces an important culinary nut. Pistacia vera often is confused with other species in the genus Pistacia that are also known as pistachio. These species can be distinguished from P. vera by their geographic distributions (in the wild) and their nuts. Their nuts are much smaller, have a strong flavor of turpentine, and have a shell that is not hard. The word pistachio is a loanword from Persian via Italian, and is a cognate to the Modern Persian word پسته Peste.
The modern pistachio nut (in the sense of P. vera) was first cultivated in Western Asia. Its cultivation spread into the Mediterranean world by way of central Iran, where it has long been an important crop. Although known to the Romans, the pistachio nut appears not to have reached the Mediterranean or most of the Near East in any quantity before medieval times.
More recently pistachio has been cultivated commercially in the English speaking world, in Australia, New Mexico,, and most notably California. The United States Department of Agriculture introduced the tree in California about 1904, but it was not promoted as a commercial crop in California until 1929. The first commercial harvest was in 1976. The 1979 Iranian Revolution gave a strong commercial impetus to the American-based pistachio nut industry. Previous to that time, most Westerners were familiar with only the slightly smaller, deeply red-hued (dyed) nuts produced mainly in Iran, where it is the second largest export after oil.
Pistachio is a desert plant, and is highly tolerant of saline soil. It has been reported to grow well when irrigated with water having 3,000-4,000 ppm of soluble salts. Pistachio trees are fairly hardy in the right conditions, and can survive temperature ranges between −10°C (14°F) in winter to 40°C (104°F) in summer. They need a sunny position and well-drained soil. Pistachio trees do poorly in conditions of high humidity, and are susceptible to root rot in winter if they get too much water and the soil is not sufficiently free draining. Long hot summers are required for proper ripening of the fruit.
The fruit is a drupe, containing an elongated seed, which is the edible portion. The seed, commonly thought of as a nut, is a culinary nut, not a botanical nut. The fruit has a hard, whitish exterior shell. The seed has a mauvish skin and light green flesh, with a distinctive flavour. When the fruit ripens, the shell changes from green to an autumnal yellow/red and abruptly splits part way open (see photo). This is known as dehiscence, and happens with an audible pop. The splitting open is a trait that has been selected by humans. Commercial cultivars vary in how consistently they split open.
Each pistachio nut weighs around 1 gram, and each pistachio tree averages around 50 kg of nuts, or around 50,000, every two years.
The trees are planted in orchards, and take approximately seven to ten years to reach significant production. Production is alternate bearing or biennial bearing, meaning the harvest is heavier in alternate years. Peak production is reached at approximately 20 years. Trees are usually pruned to size to make the harvest easier. One male tree produces enough pollen for eight to twelve nut-bearing females.
Pistachio trees are vulnerable to a wide variety of diseases (see List of pistachio diseases). Notable among these is infection by the fungus Botryosphaeria. This fungus causes panicle and shoot blight (ie, kills flowers and young shoots), and can damage entire pistachio orchards.
In California almost all female pistachio trees are the cultivar 'Kerman'. A sprig from a mature female Kerman is grafted onto a one year old rootstock. Male pistachios may be a different variety. California produces the most pistachios in the United States, and about half of these are exported, mainly to China, Japan, Europe and Canada.
Bulk container shipments of pistachio nuts are prone to self heating and spontaneous combustion because of their high fat and low water content.
|Country||Share of 2005 production|
|United States||140 000|
In research at Pennsylvania State University, pistachios in particular significantly reduced levels of low-density lipoprotein (LDL cholesterol) while increasing antioxidant levels in the serum of volunteers. In rats, consumption of pistachios as 20% of daily caloric intake increased beneficial high-density lipoprotein (HDL cholesterol) without lowering LDL cholesterol, and while reducing LDL oxidation.
On the Greek island of Chios, the husk or flesh of the pistachio fruit surrounding the shell is cooked and preserved in syrup.
The shell of the pistachio is naturally a beige colour, but it is sometimes dyed red or green in commercial pistachios. Originally the dye was applied by importers to hide stains on the shells caused when the nuts were picked by hand. However most pistachios are now picked by machine and the shells remain unstained, making dyeing unnecessary (except that some consumers have been led to expect coloured pistachios). Roasted pistachio nuts can be artificially turned red if they are marinated prior to roasting in a salt and strawberry marinade, or salt and citrus salts.