The pistachio (, UK also ; Pistacia vera) is a small to medium-sized tree of the cashew family. The tree produces seeds that are widely consumed as food. Pistachios can be used as an ingredient in desserts, chocolate, candy, ice cream, and as a paste or butter. As a tree nut, pistachios are considered a priority allergen that may induce allergic reactions in susceptible people. In 2024 the world production of pistachios was 1.4 million tonnes, with the United States, Iran, and Turkey combined accounting for 87% of the total.
Description The tree grows up to 10 metres (33 feet) tall. It has deciduous, pinnate leaves 10–20 centimetres (4–8 inches) long. The plants are dioecious, with separate male and female trees. The flowers are apetalous and unisexual and borne in panicles.
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, cream-colored exterior shell. The seed has a mauve-colored skin and light green flesh, with a distinctive flavor. When the fruit ripens, the shell changes from green to an autumnal yellow/red and abruptly splits partly open. This is known as dehiscence and happens with an audible pop. Humans selected the trait of splitting open. Commercial cultivars vary in how consistently they split open. Each mature pistachio tree averages around 50 kilograms (110 pounds) of seeds, or around 50,000 seeds, every two years.
Etymology Pistachio is from late Middle English pistace, from Old French, superseded in the 16th century by forms from Italian pistacchio, via Latin from Greek πιστάκιον pistákion, ultimately deriving from Middle Persian pistakē, meaning "pestle" (cf. pesto).
Distribution and habitat 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 temperatures ranging between −10 °C (14 °F) in winter and 48 °C (118 °F) in summer. They need a sunny position and well-drained soil. Pistachio trees do poorly in high humidity conditions 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.
Cultivation The pistachio tree may live up to 300 years. The trees are planted in orchards, and take around 7 to 10 years to reach significant production. Production is alternate-bearing (biennial-bearing), meaning the harvest is heavier in alternate years. Peak production is reached around 20 years. Trees are usually pruned to size to make the harvest easier. One male tree produces enough pollen for 8 to 12 drupe-bearing females. In the United States and Greece, the fruit is often harvested with equipment to shake the drupes off the tree. After hulling and drying, pistachios are sorted according to open-mouth and closed-mouth shells, then roasted or processed by special machines to produce pistachio kernels.
Diseases and environment
Pistachio trees are vulnerable to numerous diseases and infestation by insects such as Leptoglossus clypealis in North America. Among these is infection by the fungus Botryosphaeria, which causes panicle and shoot blight (symptoms include death of the flowers and young shoots), and can damage entire pistachio orchards. In 2004, the rapidly growing pistachio industry in California was threatened by panicle and shoot blight first discovered in 1984. In 2011, anthracnose fungus caused a sudden 50% loss in the Australian pistachio harvest. Several years of severe drought in Iran around 2008 to 2015 caused significant declines in production.
Commercial production
In 2024, world production of pistachios (in shells) was 1.4 million tonnes (3.1 billion pounds), with the United States, Turkey, and Iran together accounting for 87% of the total (table). In 2023, the state of California produced 99% of the pistachios grown in the United States, with more than 428,000 acres (173,000 ha) devoted to the crop in 2022.
Water needs In a typical California orchard of 1 acre (0.40 ha), pistachios require over 1,000,000 US gal (3,800,000 L) of water per year, an amount adding stress to the state's water problem. Nearly all California pistachios grow in state regions classified as having extremely high water stress.
Toxicity As with other tree seeds, aflatoxin is found in poorly harvested or processed pistachios. Aflatoxins are potent carcinogens produced by molds such as Aspergillus flavus and A. parasiticus. The mold contamination may occur from soil or poor storage and be spread by pests. High levels of mold growth typically appear as gray to black filament-like growth. Eating mold-infected and aflatoxin-contaminated pistachios is unsafe. Aflatoxin contamination is a frequent risk, particularly in warmer and humid environments. Food contaminated with aflatoxins has caused frequent outbreaks of acute illnesses in parts of the world. In some cases, such as in Kenya, this has led to several deaths. Pistachio shells typically split naturally before harvest, with a hull covering the intact seeds. The hull protects the kernel from invasion by molds and insects, but this hull protection can be damaged in the orchard by poor orchard management practices, by birds, or after harvest, which makes exposure to contamination much easier. Some pistachios undergo a so-called "early split", wherein both the hull and the shell split. Damage or early splits can lead to aflatoxin contamination. In some cases, a harvest may be treated to keep contamination below strict food safety thresholds; in other cases, an entire batch of pistachios must be destroyed because of aflatoxin contamination. Like other members of the family Anacardiaceae (which includes poison ivy, sumac, mango, and cashew), pistachios contain urushiol, an irritant that can cause allergic skin reactions. Large quantities of pistachios are self-heating in the presence of moisture due to their high oil content in addition to naturally occurring lipases, and can spontaneously combust if stored with a combustible fabric such as jute.
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