Sichuan pepper, Szechwan pepper or Szechuan pepper, a common spice used in Asian cuisine, is derived from at least two species of the global genus Zanthoxylum, including Z. simulans and Z. bungeanum. The botanical name comes from the Greek xanthon xylon (ξανθὸν ξύλον), meaning "blond wood." It refers to the brightly coloured sapwood possessed by several of the species. The genus belongs in the rue or citrus family, and, despite its name, is not closely related to either black pepper or chili pepper.
The husk or hull (pericarp) around the seeds may be used whole, especially in Szechuan cuisine, and the finely ground powder is one of the blended ingredients for the five-spice powder. It is also used in traditional Chinese medicine. The pericarp is the part that is most often used, but the leaves of various species are used as well in some regions of China.
Another cousin native to China is Zanthoxylum schinifolium, called xiang-jiao-zi (香椒子, lit. "aromatic peppercorn") or qing-hua-jiao (青花椒, lit. "greenish-black flower pepper"), used as spice in Hebei. Yet another Zanthoxylum species provides the African spice uzazi. Because all 250 or so species of the genus seem to possess at least some of the aromatic and complex chemicals that enliven food, it is likely that most Zanthoxylum species have been used at some time as a spice.
While the exact flavour and composition of different species from the Zanthoxylum genus varies, the same essential characteristics are present to some degree in most of them. Thus, while the terms "Sichuan pepper" and "sanshō" may refer specifically to Z. simulans and Z. piperitum, respectively, the most commonly used varieties of the pepper (such as these two) are interchangeable in most cases. Outside of scientific literature, it is common to see the names used interchangeably or as blanket terms for whichever particular species of pepper is available.
Related species are used in the cuisines of Tibet, Bhutan, Nepal, Thailand and the Konkani and Toba Batak peoples. In Bhutan this pepper is known as 'thinge' and is used liberally in preparation of soups, gruels and phaag sha paa (pork slices).
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Sichuan pepper is known in Chinese as huājiāo (花椒; literally "flower pepper"). A lesser-used name is shānjiāo (山椒; literally "mountain pepper"; not to be confused with Tasmanian mountain pepper[excessive detail?]), which is also the root of the Japanese sanshō (山椒). Confusingly, the Korean sancho (산초, 山椒) refers to a different if related species (Z. schinifolium), while Z. piperitum is known as chopi (초피).
The name hua jiao (lit. "flower pepper") in a strict sense refers to the Northern China peppercorn, Zanthoxylum bungeanum, or at least that appears to be the common consensus in current scholarly literature. However, hua jiao is also the generic term in commerce for all such viable spices harvested from the genus. This includes Z. simulans Hance), identified by a taxonomical authorities as the ye hua jiao (野花椒, lit. "wild peppercorn"), though elsewhere given as chuan-jiao (川椒, lit. "Sichuan pepper"), leading to the contention to hail this the bona fide "Sichuan pepper".
The Indian subcontinent uses a number of varieties of Sichuan pepper. In Konkani it is known as tephal or tirphal. In Nepali, Z. alatum is known as timur (टिमुर), while in Tibetan, it is known as yer ma (གཡེར་མ) and in Bhutan as thingay.It is also called current mirchi commonly.
In America, it is possible to come across names such as "Szechwan pepper," "Chinese pepper," "Japanese pepper," "aniseed pepper," "Sprice pepper," "Chinese prickly-ash," "Fagara," "sansho," "Nepal pepper," "Indonesian lemon pepper," and others, sometimes referring to specific species within this group, since this plant is not well known enough in the West to have an established name. Some brands also use the English description "Dehydrated Prickly Ash" since Sichuan pepper, and Japanese sansho, are from related plants that are sometimes called prickly ash because of their thorns (Note however that purveyors in the US do sell native prickly ash species (Z. americanum), because it is recognized as a folk remedy).
Culinary uses 
Sichuan pepper has a unique aroma and flavour that is not hot or pungent like black, white or chili peppers. Instead, it has slight lemony overtones and creates a tingly numbness in the mouth (caused by its 3% of hydroxy alpha sanshool) that sets the stage for hot spices. According to Harold McGee in On Food and Cooking, second edition, p429 they are not simply pungent; "they produce a strange, tingling, buzzing, numbing sensation that is something like the effect of carbonated drinks or of a mild electrical current (touching the terminals of a nine-volt battery to the tongue). Sanshools appear to act on several different kinds of nerve endings at once, induce sensitivity to touch and cold in nerves that are ordinarily nonsensitive, and so perhaps cause a kind of general neurological confusion."
Recipes often suggest lightly toasting the tiny seedpods, then crushing them before adding them to food. Only the husks are used; the shiny black seeds are discarded or ignored as they have a very gritty sand-like texture. It is generally added at the last moment. Star anise and ginger are often used with it prominently in spicy Sichuan cuisine. It has an alkaline pH and a numbing effect on the lips when eaten in larger doses. Ma la (Chinese: 麻辣; pinyin: málà; literally "numbing and spicy"), common in Sichuan cooking, is a combination of Sichuan pepper and chili pepper, and it is a key ingredient in má là hot pot, the Sichuan version of the Chinese traditional dish. It is also a common flavouring in Sichuan baked goods such as sweetened cakes and biscuits.
Sichuan pepper is also available as an oil (Chinese: 花椒油, marketed as either "Sichuan pepper oil", "Bunge Prickly Ash Oil", or "Hwajiaw oil"). In this form it is best used in stir-fry noodle dishes without hot spices. The preferred recipe includes ginger oil and brown sugar cooked with a base of noodles and vegetables then rice vinegar and Sichuan pepper oil are added after cooking.
Hua jiao yan (simplified Chinese: 花椒盐; traditional Chinese: 花椒鹽; pinyin: huājiāoyán) is a mixture of salt and Sichuan pepper, roasted and browned in a wok and served as a condiment to accompany chicken, duck and pork dishes. The peppercorns can also be lightly fried in order to make a spicy oil with various uses.
In Indonesian Batak cuisine, Andaliman (a relative of sichuan pepper) is ground and mixed with chilis and seasonings into a green sambal Tinombur or chili paste, to accompany grilled pork, carp and other regional specialities. Arsik in one of Batak Tapanuli dishes which use Andaliman as spice.
Sichuan pepper is one of the few spices important for Nepali (Gurkha), Tibetan and Bhutanese cookery of the Himalayas, because few spices can be grown there. One Himalayan specialty is the momo, a dumpling stuffed with vegetables, cottage cheese or minced yak meat, buff (water buffalo meat) or pork and flavoured with Sichuan pepper, garlic, ginger and onion is served with tomato and Sichuan pepper based gravy. Nepalese style chow-mein are steamed and served dry, together with a fiery Sichuan pepper sauce.
It is believed that it can sanitize meat that may not be so fresh, although in reality it may only mask foul flavours. The foul-smell masking property of Sichuan pepper made it popular in offal dishes.
Important aromatic compounds of various Zanthoxylum species include:
- Z. fagara (Central & Southern Africa, South America) — alkaloids, coumarins (Phytochemistry, 27, 3933, 1988)
- Z. simulans (Taiwan) — Mostly beta-myrcene, limonene, 1,8-cineole, Z-beta-ocimene (J. Agri. & Food Chem., 44, 1096, 1996)
- Z. armatum (Nepal) — linalool (50%), limonene, methyl cinnamate, cineole
- Z. rhesta (India) — Sabinene, limonene, pinenes, para-cymene, terpinenes, 4-terpineol, alpha-terpineol. (Zeitschrift f. Lebensmitteluntersuchung und -forschung A, 206, 228, 1998)
- Z. piperitum (Japan [leaves]) — citronellal, citronellol, Z-3-hexenal (Bioscience, Biotechnology and Biochemistry, 61, 491, 1997)
- Z. acanthopodium (Indonesia) — citronellal, limonene
US import ban 
From 1968 to 2005, the United States Food and Drug Administration banned the importation of Sichuan peppercorns because they were found to be capable of carrying citrus canker (as the tree is in the same family, Rutaceae, as the genus Citrus). This bacterial disease, which is very difficult to control, could potentially harm the foliage and fruit of citrus crops in the U.S. It was never an issue of harm in human consumption. The import ban was only loosely enforced until 2002. In 2005, the USDA and FDA lifted the ban, provided the peppercorns are heated to around 70 °C (158 °F) to kill the canker bacteria before import.
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- Gernot Katzer's spice pages