Turmeric processing
Practical Action
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 colour of the dried turmeric.
Because the fingers and bulbs are of different size and thickness to each other, it is important
that they are cured in different batches. The curing time is dependent on the age, variety and
size and thickness of the rhizomes and varies from one to four or sometimes six hours. It is also
affected by the size of the batch – smaller batches generally produce a higher quality dried
turmeric as the curing process is easier to control and monitor. It is recommended to use
perforated containers with a capacity of 50-75kg. The perforated containers are immersed in the
boiling water for the required cooking time. This method allows the boiling water to be used for
more than one batch of turmeric.
The best time for curing is two to three days after harvest. If it is delayed after this then the
rhizomes may start to deteriorate.
The benefits of curing turmeric include the following:
Reduction of drying time
More even colour distribution throughout the rhizome
A more attractive (not wrinkled) product that is easier to polish
Sterilisation of the rhizomes before drying.
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 a 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. Figure 3 shows a simple turmeric slicing machine
designed in Bolivia. It is a simple structure that contains a
transmission system and two stainless steel circular blades.
The machine is easy to build and maintain and can cut up
to 120kg turmeric per hour.
The cooked fingers or bulbs are dried until they have a final
moisture content of 5-10%. An experienced turmeric
processor will know when the rhizome is dry enough as the
Figure 2: A simple slicing
machine used in Bolivia.
fingers will snap cleanly with a metallic sound. Traditionally
the rhizome pieces are laid on clean concrete floors and
dried in the sun. This method can take anything from 10 to
15 days, depending on the climate and the size of the
rhizome pieces. It is important that the rhizome pieces are not placed in direct sunlight as this
will cause the colour to fade. Using a mechanical drier will result in a better colour and a higher
quality product.
There are several different types of mechanical drier 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 coloured product. See
the Practical Action Technical Brief on drying for further general information on driers.
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