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How long have pistachio nuts been around?
There is plenty of evidence suggesting that pistachio nuts were popular thousands of years ago. The pistachio tree probably originated in western Asia and Asia Minor, but it is found growing wild as far eastward as Pakistan and India. In Iran and Afghanistan, the nuts from wild pistachio trees are smaller than cultivated varieties, and they have an unusual, rather sharp, taste. This appeals to the nomadic tribes that live in these remote, inhospitable regions. Historically, the wild pistachio has been to the Asian nomad what the pine nut once was to the Indian in the American Southwest.
Where do pistachio nuts grow?
Most of the world?s pistachios are produced in Iran, Turkey and California. Some pistachio nuts are also grown in Syria, Afghanistan, Italy, India, Greece, Pakistan and Tunisia.
For hundreds of years pistachios have mostly been harvested from wild or semi-wild trees in the Middle East and Central Asia. However, around 1900, it became apparent that pistachios could be marketed profitably in the U.S. and Europe. Therefore, attention was devoted to developing formal, cultivated pistachio orchards, mainly in Iran and Turkey. In Afghanistan, small nuts that have the perfect green color are still harvested from wild trees. Unfortunately many wild pistachio trees have been eliminated due to forest clearance, destructive grazing by goats and the use of pistachio wood for making charcoal.
In Iran several excellent cultivars have recently been developed. In fact, Iran was the top supplier of pistachio nuts to the U.S. in 1979, providing 20 million pounds of nuts. When American hostages were seized in Iran and imports were cut back, the total of pistachios imported in the U.S. from Iran fell to 1 million pounds. As of now, there is so much political turmoil in Iran that the pistachio trade has been disrupted entirely, and prices have skyrocketed.
Another large supplier of pistachios to the U.S. is Turkey. Turkey has also selected and developed some promising cultivars. Most of the Turkish pistachio nuts come from the dry, barren foothills in western and southeastern Turkey.
What is the pistachio?
The pistachio is a member of the same botanic family (Anacardiaceae) as cashew, mango, sumac and poison oak. There are about a dozen or so species of Pistacia. Some, such as P. terebinthus, the ?turpentine tree? of Cyprus, exude turpentine. In fact, the turpentine of this species is so superior in quality to the common turpentine from the Scotch Pine, that it sells for a much higher price. Others, especially the mastic tree (P. lentiscus), are a source of a high-grade resin from which transparent varnishes are made, and of mastic, the main ingredient used in the Orient in the manufacture of chewing gum. In Turkey mastic is also used in the production of liquor. A few Pistacia trees produce small nuts. In the Middle East, an excellent edible oil is made from the very small, crushed nuts of P. terebinthus and P. atlantica. P. terebinthus, is the terebinth tree of the Bible, whose spreading branches provided shade for nomadic wanderers of patriarchal age.
The edible nuts of commerce that we are familiar with are produced only by P. vera, though seedlings of the aforementioned two species are used as rootstocks for budding and grafting P. vera.
How does the pistachio grow?
The pistachio tree grows slowly, eventually reaching a height and spread of 25 to 30 feet. It has no problem growing in poor soil and adverse climate conditions, such as low annual rainfall and stony terrain. It can grow quite well on steep, rocky slopes suitable only for goats. Though it can endure drought, it cannot survive in wet earth, thus it is very important to ensure the soil is well-drained. It grows best where winters are cool enough to break bud dormancy and where summers are long and hot enough for proper ripening of the nuts. The tree can handle cold and wind but not dampness and high humidity. Some of the areas in Iran where pistachios flourish have temperatures ranging from 15°F in the winter to over 110°F in the summer. The pistachio is a good candidate for developing some arid regions throughout the third world, where it is almost impossible to grow any other crop because of low rainfall.
A major difference between the pistachio and other popular dessert nuts is the characteristic green of its kernel. The entire kernel, not just its surface, has this coloration. Generally, nuts of a deeper green shade are more valued. The fruit grows in clusters, resembling grapes. The oblong kernel is covered with a thin, ivory-colored bony shell. When conditions are favorable, the shells split longitudinally prior to harvest, having the appearance of a laughing face. This is a desirable characteristic since the nuts are usually marketed in-shell, and when the shell is split it is easier to extract with the fingers. In unfavorable weather or other adverse conditions during nut growth and development, the shells remain closed. Turkish growers have a sorrowful expression to describe this unfortunate turn of events: ?Too bad, the pistachios are not laughing.? Unsplit nuts are not popular with the consumer and sell for a lower price.
How are pistachios cultivated?
The pistachio is usually propagated in California by budding or grafting selected scions of P. vera onto seedling rootstocks of P. atlantica, P. terebinthus and P. integerimma, These rootstock species are used because of their vigor and resistance to nematodes and soil borne fungi.
The pistachio is dioecious: male and female flowers, both of which are small and without petals, are borne on separate trees. The pollen is carried from male to female flowers by the wind. In California, Kerman is the most common female cultivar, while Peters is a prolific pollen producer. One male Peters tree can easily pollinate 8 or 10 female Kerman trees. When male trees are planted in an orchard, they are placed in locations where they will take advantage of prevailing winds.
The orchard should be established in deep, friable, well-drained soils to obtain maximum growth and productivity. Young pistachio trees are generally spaced 11 to 15 feet between trees in the row, and 22 to 30 feet between rows, depending upon soil conditions. Years later, when the trees become crowded, every other tree in the row may be removed to leave the remaining trees on a square.
Pruning is important during the early years of an orchard. High-headed trees permit easy maintenance with mechanical orchard equipment. Strong crotches should be developed to withstand the stress later on of power-driven shakers during the harvest.
Pistachio trees begin producing nuts in about 6 or 7 years. However, it is usually in the 15th to 20th year that full bearing is attained. 50 pounds of dry, hulled nuts per tree is a considered a good harvest. The trees do tend to bear a heavy crop one year, followed by little or none the following year, in a system of ?biennial bearing?. A pistachio tree can live and produce for centuries if conditions are right. In the Kerman region of Iran, there is a pistachio tree that is seven-hundred years old.
Although the pistachio tree can produce some nuts in poor growing conditions, its highest yields occur, of course, in an optimum agricultural environment. Like other fruit and nut trees, it responds very well to proper irrigation and application of fertilizer.
The most serious plant disease threatening the growth of pistachio trees in California is Verticillium wilt, a soil-borne fungus. It can quickly kill the trees. Since this fungus is frequently found in cotton, it is not a good idea to plant pistachio trees on land that was previously used for cultivating cotton, unless the soil is fumigated prior to planting.
Where do pistachios grow in the U.S.?
The only state which produces pistachios on a commercial scale is California, with approximately forty thousand acres planted. Trial plantings have also been attempted in Arizona and New Mexico. According to the California Pistachio Association, founded in 1972 and located in Fresno, the total crop is around 80 million pounds. About one-third is exported.
A pistachio boom in California in 1928 failed in the 1930?s because American growers depended on hand labor in those days. Despite the Depression, manual labor was comparatively expensive, and could not compete with cheap foreign labor in growing, harvesting and processing the nuts. Times have changed; foreign pistachio picking and processing still depends almost entirely on hand labor, while the California industry has become thoroughly mechanized.
Foreign vs. home-grown pistachios
Outside the United States, methods of harvesting pistachios are primitive. Women do most of the work. In Iran the ripened nuts are picked by hand or knocked off the trees with poles onto burlap spread on the ground. Some are hulled as soon as possible following the harvest, but the majority is dried in the hull to be hulled at a later convenient time. At that time, the nuts are soaked in water, which enables them to be easily removed by squeezing between the fingers.
Then the nuts are usually spread out in the sun to dry on stone, concrete or earth floors. Because of these crude harvesting and hulling methods, nutshells may be blemished and stained, appearing unappetizing. Importers in the U.S. use a non-toxic, red, food-grade dye to give the nuts visual appeal. Pistachio nuts may be coated with a thin layer of cornstarch and salt.
The relative merits of home-grown vs. foreign-grown pistachios is a controversial subject. American importers of Iranian and Turkish pistachios describe California pistachios as beautiful but tasteless. The California producers, on the other hand, claim their pistachios taste about the same as the imported nuts but are larger, fresher and easier to open.
When was the pistachio introduced into the U.S.?
In 1854 the Commissioner of Patents distributed seed for experimental plantings of pistachio in California, Texas and other southern states. In 1875 a few small pistachio trees, imported from France, were planted in Sonoma, California.
During the late nineteenth century, imported pistachios were popular among American immigrants from the Middle East. They were found in ethnic food shops, especially in New York City. In the 1920?s and 1930?s the colorful red- and white-coated nuts became available to the general public. They cost 5¢ per dozen nuts in vending machines located in subway stations and other public places. In those days these small-bulk nut-vending machines accounted for most pistachio nut sales.
In the early twentieth century the U.S. Department of Agriculture assembled a collection of Pistacia species and pistachio nut varieties at the Plant Introduction Station in California. In 1929 a U.S.D.A. plant explorer visited Iran and Turkestan to study pistachios. He brought back seed selected from about 90 different sources. One of these was later named Kerman, from the district of that name in Iran. Kerman eventually developed into a most important plant cultivar because of its large nut size and high percentage of split shells.
Under normal conditions the nuts hang well and may be left on the tree until most are ripe. At that time a single shaking will bring down the bulk of the mature nuts. Sometimes, trees that have just started to bear nuts are harvested by shaking the nuts from the trees onto canvas. Otherwise most are harvested mechanically by prune- or soft fruit-type harvesting equipment which consists of a shaker and a catching frame. A conveyor belt is positioned on both sides of the tree, carrying the nuts past a primary cleaner and deleafer, then dumping them into movable bins to be hauled to the processing plant. Two skilled machine operators can harvest about 1 acre of pistachios per hour.
Soon after being harvested, pistachio nuts must be hulled and dried. In fact, this has to be accomplished within 24 hours for the nuts to maintain their high quality and unblemished appearance. There are 3 types of machines that are useful in hulling pistachios. Abrasive vegetable peeling machines produce an attractive product but are limited to a batch of no more than 50 or 60 pounds at a time. Currently the harvest in California is so large that these machines are not suitable for this purpose. Then there are modified walnut dehulling machines that are quite satisfactory. But the bulk of the crop is hulled in machines consisting of 2 parallel rubberized belts rotating in the same direction, at different speeds. The nuts are fed continuously between the adjustable belts and emerge without hulls at the other end. Then they are washed and separated from stray blanks (empty shells) and immature nuts in a float/sink mechanism, where the empty blanks will float, while the mature, filled nuts will sink.
The nuts are dried with forced air at 150°-160°, reducing the moisture content, which may have been up to 45% in the freshly harvested nuts, to 5% in about ten hours. ?Electric eye? sorters remove blemished nuts, which can be dyed red or white and sold as dyed nuts, or shelled to be sold as nutmeats. Good quality splits are graded to four sizes, roasted, salted and packaged. About 90% of California pistachios are sold roasted and salted in their shell for snacking. Shelled pistachios are used commercially in confectionery, ice cream candies, sausages, bakery goods and flavoring for puddings.
The size of pistachio nuts is expressed by the number of nuts per ounce. Iranian pistachios range from 18 to 40 nuts per ounce, while California nuts are larger ? sometimes as few as 14 to the ounce. Since pistachio kernels are rather small and expensive they are, as a rule, not included in salt mixes with other larger tree nuts. Pistachios nuts are rich in oil, but due to the high price of the nuts, it does not pay to produce pistachio oil commercially.
Tree nuts are usually marketed ?in-shell? or ?shelled?. Pistachios and filberts are usually sold ?in-shell? to the retail trade, while almonds and pecans are generally sold shelled to the industry, which consists primarily of salters, confectioners, bakers and ice cream manufacturers. The pistachio nut is unique in the nut trade due to its semi-split shells. This enables the processor to roast and salt the kernel without removing the shell, while it also serves as a convenient form of natural packaging.