Cumin is an ancient spice that is used in many cuisines around the world, but is most closely associated with the spice blends of Central Asia, particularly curry powders from India and Pakistan.
Just like caraway, the spice cumin is derived from a fruit and not a seed as is commonly believed. Cumin "seeds" grow on a delicate annual Cuminum cyminum which grows to the modest height of 60 cm. The plant has wispy foliage, resembling dill or fennel tops in its frond-like appearance.
The mature seed is harvested at around 5 mm in length and is pale brown to khaki in colour. Cumin seeds have 9 ridges running along their length (which are actually oil canals) and have a tiny filament like stem growing at one end. Mechanical sorting of cumin seeds removes around 90% of these stems, but some inevitably remain which is why you will find tiny "hairs" when you purchase cumin seeds.
Cumin is sold in two forms, whole cumin seeds and powdered cumin, which is the ground spice. Once ground, cumin has a slightly oily texture; hence stale ground cumin tends to clump together.
The spice has a warm, mildly spicy and sweet flavour that is immediately reminiscent of curry. It is no surprise as cumin is one of the major spices used in curry blends.
The use of cumin is well documented throughout history. The seeds have been found in the tombs of the Pharaohs and it predates the well known mummifying spices, cinnamon and cloves. The Romans considered cumin to be a symbol of greed and thriftiness, hence the emperor Marcus Aurelius was bestowed with the cutting nickname, Cuminus. In middle age Europe cumin represented fidelity. Germanic brides of the era would carry cumin, dill and salt as a sign of faithfulness to the groom.
Apart from the obvious curry association, cumin is often used in the famous chili dishes of the South Western US and it is frequently used in spice blends from North Africa such as chermoula, ras el hanout and harissa.
Ground cumin will deteriorate and lose its pungency more rapidly than the seed, so always try to buy the freshest powdered cumin you can find. Look for bright khaki coloured powder and eschew any that is dull and clumpy. Both the seed and powder benefit from a light toasting in a dry fry pan for 2-3 minutes before use to release more of its essential oils. As with all spices, store cumin in an airtight container and away from direct sunlight
gn0sis has reminded me that cumin is called jeera in India as well as zera in other parts of the country. To confound things a little jeera and zera refer not only to cumin, but caraway as well. Remember this if you are shopping in a sub-continental spice market!