From corm to thread

It starts with a corm

The saffron crocus doesn't grow from seed. Underground it carries a corm a little larger than a hazelnut, wrapped in a brown, fibrous tunic. A corm isn't layered like an onion. It's a solid store of food that feeds next autumn's flowers, the winter's leaves and the next generation of corms.

Each corm lives for a single season. It flowers, grows leaves and is used up. As it fades, a few daughter corms grow on top of it and beside it. That's why a saffron field renews itself every year. It isn't the same plant flowering again, but copies of it.

The size of the corm decides the flowers you get. Small corms often don't flower at all that year; they grow leaves and get bigger. Large corms give more than one flower. A good saffron year starts with large, healthy corms.

Dormancy and incubation: June – August

In May the leaves turn yellow and the corm goes dormant. From above, the field looks empty, but the most important work of the year is happening underground: the flower buds form in summer, in the warmth. Inside the corm, next October's flowers take shape, too small to see.

In the field, summer heat does this on its own. Indoors, we do it: the corms rest in the dark at a steady, warm temperature. Too much moisture now rots the corm, and too little dries it out. The aim is just enough humidity to stop it drying.

Waking and flowering: September – November

As the air cools and humidity rises, the corm wakes. A thin white sheath pushes up through the soil, and the flower often opens before the leaves or with them. Flowering is short: in a field, every flower opens and fades within two to three weeks.

Each flower holds three things:

• Three red stigmas. This is saffron: threads that widen slightly at the tip, like small trumpets.
• Three yellow anthers. They carry pollen. They aren't saffron and are removed at harvest.
• Six violet petals. Beautiful, but worth nothing as saffron.

Harvest and separation

Flowers are picked early in the morning, before or just as they open. A flower left open wilts in sun and wind, and its stigmas suffer for it. The picked flowers are cleaned the same day: three stigmas pulled from each flower by hand.

Below the stigmas is a pale yellow stalk that joins them (the style). It adds weight but gives no colour or aroma. The most valuable saffron is the red part alone.

Drying and storing

Fresh stigmas are dried the same day and lose most of their weight in the process. Methods vary by region: in Spain they're traditionally toasted briefly over gentle heat, while in Iran they're dried more slowly, in the shade. Whatever the method, the aim is the same: to keep the compounds that carry colour, bitterness and aroma.

Dried saffron is kept in a closed container, away from light, moisture and air. Powdered saffron spoils faster than threads and is far easier to fake, so buying threads is always safer.

What decides quality

Saffron's value comes from three compounds:

The international standard ISO 3632 measures all three in the laboratory and sorts saffron into categories, with Category I the highest. Good saffron in warm water releases its colour slowly, from yellow to deep gold, while the thread itself stays red.

Leaves and new corms: December – April

After flowering, thin grass-like leaves grow, each with a pale stripe down the middle. These leaves gather energy all winter, and they decide saffron's next year: as the mother corm is used up, daughter corms grow beside it on the food the leaves make. The healthier the leaf season, the larger next year's corms.

Die-back: May

As spring warms, the leaves yellow and dry. The mother corm is now just a shrivelled husk, with new corms in its place. In the field, the corms stay in the ground until the next year. Every few years they're lifted, sorted by size and replanted. Indoors, the new corms are collected and go into summer incubation.

The cycle begins again.