Processing of Turmeric
Turmeric (Scientific Name: Curcuma longa) is one of the important spice crops which is a perennial herbaceous in growing habit. The rhizome contains curcumin pigment which is used in coloring in food industry. The value added products of turmeric are oil, oleoresin, curcuminoid and dehydrated turmeric powder. Similarly, it is used in condiments and as dye in cosmetic industries.
Different processes are involved in the curing process of turmeric which can be explained in 4 stages: –
Fingers are at first separated from mother rhizomes. Mother rhizomes are usually kept as seed material. The fresh turmeric is cured for obtaining dry turmeric. Curing involves boiling of fresh rhizomes in water and drying in the sun. In traditional method of curing, the cleaned rhizomes are boiled in copper or galvanized iron or earthen vessels with water just enough to soak them. Boiling is stopped when froth comes out and white fumes appear jigging out a typical odor.
The boiling lasts for 45-60 minutes when the rhizomes are soft. The stage at which boiling is stopped largely influences the color and the aroma of the final product. Over cooking spoil, the color of the final product and under cooking renders the dried product brittle. The improved scientific method of curing is performed in perforated trough of galvanized iron sheet which is immersed in pan of water. Then the fingers are boiled till they become soft. The cooked turmeric is taken out of the pan by lifting the trough and draining the water into the pan itself. The same hot water in the pan can be used for boiling next phase of raw turmeric.
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The cooked fingers are dried in the sun by spreading in 5-7 cm thick layers on bamboo mats or drying floor. A thinner layer is not desirable as the color of the dried product may be adversely affected. During night time, the material should be heaped or covered. It may take 10-15 days for the rhizomes to become completely dry. Artificial drying using cross flow hot air at a maximum temperature of 60 degree Celsius is also found to give a satisfactory product. The yield of dry turmeric varies from 20-30 % of fresh harvest depending upon the variety and location where the crop is grown.
The dried turmeric has a poor appearance and rough dull color outside the surface with scales and root bits. The appearance is improved by smoothening and polishing the outer surface by manual or mechanical rubbing. Manual polishing the outer surface by manual or mechanical rubbing. Manual polishing consists of rubbing the dried turmeric fingers on a hard surface or trampling them under feet wrapped with gunny bags. The improved method is by using hand operated barrel or drum mounted on a central axis, the sides of which are made of expanded metal mesh. When the drum is filled with turmeric and rotated, polishing is affected by abrasion of the surface against the mesh as well as by mutual rubbing against each other as they roll inside the drum. The turmeric is also polished in power operated drums. The yield of polished turmeric forms the raw material varies from 12-25%.
The color of the turmeric always attracts the buyers. However, to impart the attractive yellow color to the turmeric, turmeric suspension in water is added to the polishing drum in the last ten minutes. When the rhizomes are uniformly coated with suspension, then they may be dried in the sun. after polishing it should be kept in clean sacks and stored over wooden pallets in stores. Stores should be clean, free from infestation of pests, spiders and rodents. Pesticides should not be applied on the dried / polished turmeric to prevent storage pest attack.