Authors; Karim Yar Abbasi, Dr. CM Ayyub, Saqib Ayyub
Turmeric (Curcuma domestica) is an erect perennial plant grown as an annual crop for its rhizome (underground rootlike stem bearing roots and shoots). It belongs to the same family as ginger (Zingiberaceae) and grows in the same hot and humid tropical climate. The rhizome is a deep bright yellow color and similar in form to the ginger but slightly smaller. The plant originated in the Indian sub-continent and today India is the world’s leading producer and consumer of turmeric. It is also produced in China, Taiwan, Bangladesh, Indonesia, Sri Lanka, Australia, Africa, Peru, and the West Indies. Turmeric plays an important role in Indian culture- it is an essential ingredient of curry, used in religious festivals, as a cosmetic, a cloth dye, and in many traditional health remedies. The spice is sometimes referred to as ‘Indian saffron.
The Turmeric plant is propagated by planting pieces of the previous season’s rhizome, which grows to form plants of about 0.9 meters tall. The plant has long-stemmed leaves and pale-yellow flowers and requires loamy soil. It grows in a wide range of climatic conditions but does require rainfall of between 1000 and 2000mm a year. It can grow in locations that are up to 1220m above sea level.
Turmeric is harvested when the plants are between 7 and 10 months of age when the stems and leaves start to dry out and die back. The whole plant is removed from the ground, taking care not to cut or bruise the rhizomes.
The leaves are removed from the plant and the roots are carefully washed to remove soil. Any leaf scales and long roots are trimmed off. The side (lateral) branches (which are known as the fingers) of the rhizomes are removed from the main central bulb (known as the mother). The mothers and fingers are heaped separately, covered in leaves, and left to sweat for one day. The ‘mothers’ are the preferred material for planting the following year.
Before drying, the turmeric rhizomes have to be cured. This involves boiling the roots to soften them and remove the raw odor. After curing, the starch is gelatinized, which reduces the drying time required, and the color is uniformly distributed throughout the rhizome. The specifications for curing turmeric vary from different places. The Indian Institute of Spice Research and the Agricultural Research Centre recommend boiling in plain water for 45 minutes froth appears on the surface and the typical turmeric aroma is released. Using this method, the color will deteriorate if the rhizomes are boiled for too long. However, if not boiled for long enough, the rhizome will be brittle. The optimum stage is reached when the rhizomes are soft to touch or can be pierced by a blunt piece of wood.
Other researchers recommend boiling the rhizomes in an alkaline solution, made from 0.05% to 1.0% sodium carbonate or lime (calcium carbonate). The alkaline water is thought to improve the final color of the dried turmeric.
The benefits of curing turmeric include the following:
• Reduction of drying time
• More even color distribution throughout the rhizome
• A more attractive (not wrinkled) product that is easier to polish
• Sterilization of the rhizomes before drying.
The rhizomes are sliced before drying to reduce the drying time and improve the quality of the final product (it is easier to achieve lower final moisture content in small pieces of rhizome without spoiling the appearance of the product). The rhizomes are traditionally sliced by hand, but there are small machines available to carry out this process.
There are several different types of mechanical driers that are suitable for drying turmeric. These include the tray drier, cross-flow air tunnels, solar driers, and cabinet driers. The optimum drying temperature is 60°C – temperatures higher than this result in a darker colored product. See the Practical Action Technical Brief on drying for further general information on driers.
After drying the rhizomes are polished to remove the rough surface. This can be done by hand or by shaking the rhizomes in a gunny bag filled with stones. Polishing drums are used in many places – these are very simple, power-driven drums that have an abrasive metallic mesh lining. In some places the rhizomes are sprinkled with a solution of ground turmeric in water during the final polishing, to give the rhizomes a good color.
Grinding can be a method of adding value to a product. However, in general, it is not advisable to grind spices as they become more vulnerable to spoilage. The flavor and aroma compounds are not stable and will quickly disappear from ground products. The storage life of ground spices is much less than for the whole species. It is very difficult for the consumer to judge the quality of ground spice. It is also very easy for unscrupulous processors to contaminate the ground spice by adding other materials. Therefore, most consumers, from wholesalers to individual customers, prefer to buy whole spices. Turmeric is one of the few spices that is usually purchased in ground form. The whole rhizome pieces may be exported and then ground in the country of destination. Alternatively, the dried rhizomes may be ground at the place of origin. Grinding is a very simple process that involves cutting and crushing the rhizomes into small particles, then sifting it through a series of screens of different mesh sizes, to get a fine powder. There is a range of grinding mills available, both manual and powered, of different capacities and which work in different ways. The traditional way to grind would be between two stones. The advantage of this method is that the turmeric does not get too hot during the grinding process. With some of the mechanical mills, such as a hammer mill, heat is generated during the grinding process, which can cause some of the volatile taste and aroma compounds to be lost. For higher quality ground turmeric, the grinding temperature should be kept as low as possible. After grinding the powder is sieved through different mesh screens until a uniform, fine powder is obtained.
The bulk rhizomes are stored in a cool and dry environment, away from direct sunlight. The bright color of ground turmeric will fade when it is left at the light for a long period of time. Therefore, the packets should be stored in a cardboard box, away from the sunlight. The storage room should be clean, dry, cool, and free from pests. Mosquito netting should be fitted on the windows to prevent pests and insects from entering the room. Strong smelling foods, detergents, and paints should not be stored in the same room.
The Health Benefits of Turmeric
In the western world, we’re seeing a growing interest in turmeric due to its incredible health properties. It possesses powerful anti-inflammatory, anti-tumor, and antioxidant properties, due to its curcumin content.
In case you weren’t aware, the yellow food coloring agent E 100 is actually curcumin derived from turmeric.
The medicinal properties of curcumin are recognized and well-documented, and science is able to explain how it works. For those interested, here’s an explanation, quoted from the US government’s National Cancer Institute:
“Curcumin is a phytopolylphenol pigment isolated from the plant Curcuma longa, commonly known as turmeric, with a variety of pharmacologic properties. Curcumin blocks the formation of reactive oxygen species, possesses anti-inflammatory properties as a result of inhibition of cyclooxygenases (COX) and other enzymes involved in inflammation; and disrupts cell signal transduction by various mechanisms including inhibition of protein kinase C. These effects may play a role in the agent’s observed antineoplastic properties, which include inhibition of tumor cell proliferation and suppression of chemically induced carcinogenesis and tumor growth in animal models of cancer.”