Introduction

Saffron is a spice derived from the flower of the saffron crocus (Crocus sativus). Crocus is a genus in the family Iridaceae. A C. sativus flower bears three stigmas, each the distal end of a carpel. Together with the styles — stalks that connect the stigmas to their host plant — the dried stigmas are used in cooking as a seasoning and colouring agent. Saffron, long the world's most expensive spice by weight, is native to Southwest Asia.
Saffron's bitter taste and iodoform- or hay-like fragrance result from the chemicals picrocrocin and safranal. Saffron also contains a carotenoid dye, crocin, which imparts a rich golden-yellow hue to dishes and textiles.
In the EU saffron is identified as E164 under the E number food additive code system.

Etymology
The English word saffron stems from the Latin word safranum via the 13th-century Old French term safran. Safranum in turn derives from Persian زعفران (za'ferân). Some argue that it ultimately came from the Arabic word زَعْفَرَان (za'farān), which itself derives from the adjective أَصْفَر (asfar, "yellow"). However, some etymologists argue that زَعْفَرَان (za'farān) is the arabicized form of the Persian word زرپران (zarparān) — "having golden stigmas". Latin safranum is also the source of the Italian zafferano, Portuguese açafrão and Spanish azafrán etc. Crocum in Latin is a Semitic loan word derived from Aramaic kurkema via Arabic kurkum, and Greek krokos.

One part saffron to 150,000 parts water will turn the water a bright yellow and still leave its distinctive flavor.

Biology

The domesticated saffron crocus (Crocus sativus) is an autumn-flowering perennial plant unknown in the wild. Saffron in high dosage can also be poisonous. It is a sterile triploid form, possibly of the eastern Mediterranean autumn-flowering Crocus cartwrightianus that originated in Central Asia. The saffron crocus resulted when Crocus cartwrightianus was subjected to extensive artificial selection by growers seeking longer stigmas. Being sterile, the purple flowers of Crocus sativus fail to produce viable seeds; reproduction depends on human assistance: corms, underground bulb-like starch-storing organs, must be dug up, broken apart, and replanted. A corm survives for one season, producing via this division up to ten "cormlets" that grow into new plants. Corms are small brown globules up to 4.5 centimetres (1.8 in) in diameter and are shrouded in a dense mat of parallel fibers.

After aestivating in spring, the plant sends up five to eleven narrow and nearly vertical green leaves, each up to 40 cm (16 in) in length. In autumn, purple buds appear. Only in October, after most other flowering plants have released their seeds, do its brilliantly hued flowers develop; they range from a light pastel shade of lilac to a darker and more striated mauve. Upon flowering, plants average less than 30 cm (12 in) in height. A three-pronged style emerges from each flower. Each prong terminates with a vivid crimson stigma 25–30 mm (0.98–1.2 in) in length.

Cultivation

Crocus sativus thrives in the Mediterranean maquis (an ecotype superficially resembling the North American chaparral) and similar climates where hot, dry summer breezes sweep semi-arid lands. It can nonetheless survive cold winters, tolerating frosts as low as −10 °C (14 °F) and short periods of snow cover.

Irrigation is required if not grown in moist environments such as Kashmir, where annual rainfall averages 1,000–1,500 mm (39–59 in); saffron-growing regions in Greece (500 mm or 20 in annually) and Spain (400 mm or 16 in) are far drier than where Crocus is cultivated in Iran, for example. What makes this possible is the timing of the local wet seasons; generous spring rains and drier summers are optimal. Rain immediately preceding flowering boosts saffron yields; rainy or cold weather during flowering promotes disease and reduces yields. Persistently damp and hot conditions harm the crops, and rabbits, rats, and birds cause damage by digging out the corms. Nematodes, leaf rusts, and corm rot pose added threats.

The plants fare poorly in shady conditions; they grow best in full sunlight. Fields that slope towards the sunlight are optimal (i.e., south-sloping in the Northern Hemisphere). Planting is mostly done in June in the Northern Hemisphere, where corms are lodged 7 to 15 centimetres (2.8–5.9 in) deep. Planting depth and corm spacing, in concert with climate, are critical factors in determining yields. Mother corms planted deeper yield higher-quality saffron, though form fewer flower buds and daughter corms. Italian growers optimize thread yield by planting 15 centimetres (5.9 in) deep and in rows 2–3 cm apart; depths of 8–10 cm optimizes flower and corm production. Greek, Moroccan, and Spanish growers have devised distinct depths and spacings to suit their locales.

C. sativus prefers friable, loose, low-density, well-watered, and well-drained clay-calcareous soils with high organic content. Traditional raised beds promote good drainage. Soil organic content was historically boosted via application of some 20–30 tonnes of manure per hectare. Afterwards—and with no further manure application—corms were planted. After a period of dormancy through the summer, the corms send up their narrow leaves and begin to bud in early autumn. Only in mid-autumn do they flower. Harvests are by necessity a speedy affair: after blossoming at dawn, flowers quickly wilt as the day passes. All plants bloom within a window of one or two weeks. Roughly 150 flowers yield 1 gram (0.035 oz) of dry saffron threads; to produce 12 g of dried saffron (72 g freshly harvested), 1 kg of flowers are needed (1 lb for 0.2 oz of dried saffron). One fresh-picked flower yields an average 30mg (0.03g) of fresh saffron or 7mg (0.007g) of dried saffron.

Chemistry

Saffron contains more than 150 volatile and aroma-yielding compounds. It also has many nonvolatile active components, many of which are carotenoids, including zeaxanthin, lycopene, and various α- and β-carotenes. However, saffron's golden yellow-orange colour is primarily the result of α-crocin. This crocin is trans-crocetin di-(β-D-gentiobiosyl) ester (systematic (IUPAC) name: 8,8-diapo-8,8-carotenoic acid). This means that the crocin underlying saffron's aroma is a digentiobiose ester of the carotenoid crocetin. Crocins themselves are a series of hydrophilic carotenoids that are either monoglycosyl or diglycosyl polyene esters of crocetin. Meanwhile, crocetin is a conjugated polyene dicarboxylic acid that is hydrophobic, and thus oil-soluble. When crocetin is esterified with two water-soluble gentiobioses (which are sugars), a product results that is itself water-soluble. The resultant α-crocin is a carotenoid pigment that may comprise more than 10% of dry saffron's mass. The two esterified gentiobioses make α-crocin ideal for colouring water-based (non-fatty) foods such as rice dishes.

The bitter glucoside picrocrocin is responsible for saffron's flavour. Picrocrocin (chemical formula: C16H26O7; systematic name: 4-(β-D-glucopyranosyloxy)-2,6,6- trimethylcyclohex-1-ene-1-carboxaldehyde) is a union of an aldehyde sub-element known as safranal (systematic name: 2,6,6-trimethylcyclohexa-1,3-diene-1- carboxaldehyde) and a carbohydrate. It has insecticidal and pesticidal properties, and may comprise up to 4% of dry saffron. Significantly, picrocrocin is a truncated version (produced via oxidative cleavage) of the carotenoid zeaxanthin and is the glycoside of the terpene aldehyde safranal. The reddish-coloured zeaxanthin is, incidentally, one of the carotenoids naturally present within the retina of the human eye.

When saffron is dried after its harvest, the heat, combined with enzymatic action, splits picrocrocin to yield D–glucose and a free safranal molecule. Safranal, a volatile oil, gives saffron much of its distinctive aroma. Safranal is less bitter than picrocrocin and may comprise up to 70% of dry saffron's volatile fraction in some samples. A second element underlying saffron's aroma is 2-hydroxy-4,4,6-trimethyl-2,5-cyclohexadien-1-one, the scent of which has been described as "saffron, dried hay like". Chemists found this to be the most powerful contributor to saffron's fragrance despite its being present in a lesser quantity than safranal. Dry saffron is highly sensitive to fluctuating pH levels, and rapidly breaks down chemically in the presence of light and oxidizing agents. It must therefore be stored away in air-tight containers in order to minimise contact with atmospheric oxygen. Saffron is somewhat more resistant to heat.

Medicinal uses
Saffron has many medicinal uses:

• A 2010 double-blind, placebo-controlled study found saffron helped mild to moderate Alzheimer's disease.
• Crocetin, an important carotenoid constituent of saffron, has shown significant potential as an anti-tumor agent in animal models and cell culture systems.[28] Saffron inhibits DMBA-induced skin carcinoma in mice when treated early.
• Animal testing has shown that the aqueous and ethanolic extracts of saffron and its constituents, crocin and safranal, have antidepressant activities in forced swimming test.
• Both saffron stigma and petals are said to be helpful for depression.
• Satiereal (Inoreal Ltd, Plerin, France), a novel extract of saffron stigma, may reduce snacking and enhance satiety through its suggested mood-improving effect, and thus contribute to weight loss.
• Saffron was found to be effective in relieving symptoms of PMS.
• Saffron, crocins and crocetin inhibit breast cancer cell proliferation.
• Crocus sativus (most saffron research refers to the stigmas but often this is not made clear in research papers) inhibits histamine H1 receptors in animals, suggesting a potential use in allergic disorders. (Histamine is a biological amine that plays an important role in allergic responses.)
• Saffron may have a protective effect on the heart.
• A 2011 double blind, human trial found use of 100 mg of saffron daily has temporary immunomodulatory activities.