What is saffron?

Saffron is a spice derived from the flower of Crocus sativus, commonly known as the "saffron crocus". The vivid crimson stigmas and styles, called threads, are collected and dried to be used mainly as a seasoning and colouring agent in food. Saffron, long among the world's most costly spices by weight, was probably first cultivated in or near Greece. C. sativus is probably a form of C. cartwrightianus, that emerged by human cultivators selectively breeding plants for unusually long stigmas in late Bronze Age Crete. It slowly propagated throughout much of Eurasia and was later brought to parts of North Africa, North America, and Oceania.
Saffron's taste and iodoform or hay-like fragrance result from the chemicals picrocrocin and safranal. It also contains a carotenoid pigment, crocin, which imparts a rich golden-yellow hue to dishes and textiles. Its recorded history is attested in a 7th-century BC Assyrian botanical treatise compiled under Ashurbanipal, and it has been traded and used for over four millennia. Iran now accounts for approximately 90% of the world production of saffron.

Different types of saffron
The best quality saffron is marked by its deep red color and full- flavor, obtained by picking only the dark red tips of the hair-like stigma of the flower.  Lower quality saffron may use more of the flower's stigma and style, and may be sold as powder (which can hide adulteration.)  Cooks can mobilize the aromas and tastes of saffron by steeping the spice fibers or powder in liquid, often warm or hot, for at least a few minutes.  Besides use in stews, broths, sauces or rice, saffron is used to flavor tea/tisanes/tinctures for drinking.
Saffron will differ according to the climate and weather and land conformation of its growing location, and the picking and processing techniques.  Saffron is cultivated mainly in regions with hot, dry summers and semi-arid land, on land that slopes toward the sun.  The Mediterranean region, especially Spain and Greece, and South Asia, especially Iran and Kashmir, are notable producers, although saffron is also produced in Southeast Asia, Oceania and the Americas.  Some of the most reputed sources/products are:
-zafferano dell'Aquila from Italy's Abruzzo region's Navelli Valley
-saffron from San Gavino Monreale, Sardinia, Italy
-Kashmiri (India) Mongra or Lacha saffron, with maroon-purple color
-Iranian Sargol grade saffron
-Spanish coupé grade saffron
-artisanal/boutique crops selectively picked for highest quality from England, France, New Zealand, Switzerland and the USA.

This kind of saffron has the highest coloring power (higher than 250 usp) among the other kinds and its volume is higher, too.

All-Red (Sargol in Persian)
This kind of saffron is similar to coupe and it is derived from Bunch saffron, i.e. the white or yellow parts of saffron threads are cut by scissors and then using static electricity they are separated from the red parts. The remaining parts are completely red and they are really pure and without style. This kind of saffron has very high coloring power (240 usp or higher).

This kind of saffron contains filaments which have 2 or 3 mm style. Its coloring power is about 220 usp.

Bunch (Dastehi in Persian):
This kind of saffron consists of both, style and red-colored stigma. It is also called Red& White in which the red part is about 70% to 75% and the style is about 25% and 30%. According to Iran's Standard, it is called filament 4%.

Style (Konj in Persian)
It is the yellow or white parts of saffron threads which are separated from Red-colored stigma. In fact, this part of saffron thread cannot de defined as pure saffron. It does 

not contain the dye, crocin that gives food a rich golden color. It is mostly applied for medicinal usages.

The various saffron crocus cultivars give rise to thread types that are often regionally distributed and characteristically distinct. Varieties (not varieties in the botanical sense) from Spain, including the tradenames "Spanish Superior" and "Creme", are generally mellower in colour, flavour, and aroma; they are graded by government-imposed standards. Italian varieties are slightly more potent than Spanish. The most intense varieties tend to be Iranian. Various "boutique" crops are available from New Zealand, France, Switzerland, England, the United States, and other countries—some of them organically grown. In the US, Pennsylvania Dutch saffron—known for its "earthy" notes—is marketed in small quantities.
Consumers may regard certain cultivars as "premium" quality. The "Aquila" saffron, or zafferano dell'Aquila, is defined by high safranal and crocin content, distinctive thread shape, unusually pungent aroma, and intense colour; it is grown exclusively on eight hectares in the Navelli Valley of Italy's Abruzzo region, near L'Aquila. It was first introduced to Italy by a Dominican monk from Inquisition-era Spain, but the biggest saffron cultivation in Italy is in San Gavino Monreale, Sardinia, where it is grown on 40 hectares, representing 60% of Italian production; it too has unusually high crocin, picrocrocin, and safranal content. Another is the "Mongra" or "Lacha" saffron of Kashmir (Crocus sativus 'Cashmirianus'), which is among the most difficult for consumers to obtain. Repeated droughts, blights, and crop failures in Kashmir combine with an Indian export ban, contribute to its prohibitive overseas prices. Kashmiri saffron is recognisable by its dark maroon-purple hue; it is among the world's darkest, which hints at strong flavour, aroma, and colouring effect.