Turmeric (Curcuma longa syn. C. domestica) is a subtropical/tropical plant which is a member of the ginger (Zingiberaceae) family, and is native to Southwest India. It’s grown traditionally as a spice, medicine and as a source of bright yellow dye. Ground turmeric root is an important culinary spice, and curry powder contains up to 25% turmeric.
The root (rhizome) of the turmeric plant has been used in Chinese and Indian medicine for thousands of years. In traditional Chinese medicine (TCM), dried turmeric rhizome is known as Jiāng Huáng, 姜黄, while in Ayurvedic (traditional Indian) medicine, it’s referred to as Haridra.
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-tumour, and antioxidant properties, due to its curcumin content.
In case you weren’t aware, the yellow food colouring agent E 100 is actually curcumin derived from turmeric.
The medicinal properties of curcumin are recognised 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.”
When is Turmeric Harvested?
Turmeric roots are harvested in winter after the plants have died down and all the leaves and stem have dried up, which occurs approximately 7 to 10 months after planting. When the plant dies back to the ground, it transfers all the nutrients into the rhizome (root) which becomes dormant over winter.
How to Dry and Powder Turmeric Root Without Fancy Equipment
Turmeric powder has been used for thousands of years, and the ancient people made it for most of that time with the most simplest equipment, and the great news is that we can too! There’s no need to buy expensive appliances such electric dehydrators and food processors for the task. It can all be done very cheaply and easily, much like the traditional way.
As some people may already have the electric appliances, we’ll explain how to use those too in the following instructions.
Step 1 – Clean the turmeric root
Wash the turmeric rhizomes thoroughly to clean off any soil adhering to them, and remove any long roots or leaf scales.
There is no need to peel the rhizomes to clean them, but just like any other root crops that are used fresh, they can be peeled if desired.
In large-scale commercial turmeric processing operations India, turmeric rhizomes are cured before drying. Curing involves boiling the rhizomes in water for 45 min to one hour, until froth appears at the surface, the typical turmeric aroma is released, and the rhizomes become soft.
This is done to gelatinise the starch so the rhizomes dry more uniformly, reducing drying time. It is also done to produce an attractive product that will appeal to buyers – to remove the raw earthy odour, to cause the colouring to diffuse evenly throughout the rhizome to produce a more uniformly coloured product, and a to remove wrinkling to make the rhizomes more suitable for polishing, a process where the outer surface is smoothed and polished by manual or mechanical rubbing.
When making turmeric powder at home, there is no need to boil the rhizomes, and it’s important to be aware that over-cooking deteriorates the colour of turmeric.
Step 2 – Slice the turmeric root into very thin pieces
For turmeric rhizomes to dry out, they need to be sliced thin, and to do this, a sharp knife and a cutting board are required.
Turmeric can stain things yellow, so if using a wooden cutting board, it’s best to use an old one as the stains may not come out.
When slicing the turmeric rhizomes with a knife, cut the slices as thin as possible, and no thicker than 3mm (1/8”).
A potato peeler can be used to create extremely thin slices which will dry very easily, but it’s a slower process.
Step 3 – Lay out sliced turmeric root to air dry
Place a sheet of greaseproof paper on a tray and lay the turmeric slices on it, trying to keep them evenly spaced and not laying on each other as much as possible.
The best spot for drying is a well-ventilated location away from direct sunlight.
When the turmeric slices become brittle and can be snapped in half, they’re dried and ready to be ground into powder.
The turmeric slices shown below were placed in a tray on a kitchen bench away from a window, and left to dry for 5-6 days in the middle of winter. The indoor temperature was 21 °C (70 °F) with a relative humidity of approximately 60%, which is maintained by the ducted gas heating.
Using an electric dehydrator – the optimum drying temperature for turmeric and ginger rhizomes is 60 ºC (140 °F) when using a dehydrator. The time required will vary between dehydrators, but the model I own (Ezidri) takes around 10 hours when the slices are less than 5mm thick.
Oven drying is not a good idea as the lowest temperature is much too hot, causing the kitchen will fill with the smell of turmeric, meaning that a lot of the volatile compounds in the spice have been lost into the air. The key active ingredient in turmeric, curcumin, has a melting point of 183 °C (361.4°F), and in studies where curcumin is used as the food colouring agent, it is recommended that processing temperature should not exceed 190 °C (374°F), as this is the temperature where the decomposition of curcumin begins.
In Indian commercial operations, turmeric is dried using cross-flow hot air at a maximum temperature of 60 ºC, or it is sun dried in the middle of summer, which may take 10 to 15 days. With large-scale sun drying, sliced rhizomes are laid out on cement floors or bamboo mats and spread into layers 5-7 cm (2-3”) thick to minimize direct sunlight which causes surface discoloration of the turmeric. At night, the rhizomes are heaped together to protect them from moisture. Using such thick layers, it is understandable why they need to boil the rhizomes in the curing process for more uniform drying.
Step 4 – Grind dried turmeric root into turmeric powder
The dried turmeric slices can be ground into turmeric powder very quickly and easily using a cheap coffee grinder, like the one shown below.
When grinding turmeric, it’s important that the crushing speed doesn’t heat up the spice too much. Heating will lead to the loss of volatile compounds, and the combination of heat and oxygen during the grinding process may cause degradation of the curcumin content.
Coffee grinders don’t heat up the turmeric powder, and create a very fine, uniform powder in a few seconds. A food processor, which are much more expensive than a coffee grinder, can also be used for the task, but may not break up the turmeric evenly, leaving larger fragments, which may lead some people to run the machine longer. When using the super high-speed food processors which can spin fast enough generate enough heat to cook meals, there is the risk of overheating the spice.If a food processor is leaving larger pieces behind after grinding, sift the powder through a fine sieve and reprocess the larger pieces only, so the fine turmeric powder doesn’t get heated unnecessarily.
The low-tech traditional method for grinding spices, which may take a bit longer, is manual grinding using a mortar and pestle. These implements have been used since ancient times to prepare ingredients by crushing and grinding them into fine powders or pastes in the kitchen, laboratory, and pharmacy. You can purchase a quality a mortar and pestle cheaply from good kitchen supply stores, and they will last forever.
Here is the turmeric powder that was ground with a coffee grinder, which took less than a minute. It has the characteristic turmeric colour, looks great, and made from home-grown turmeric!
Step 5 – Store turmeric powder
Turmeric powder should be stored in an glass jar with tight-fitting lid which is kept in a dark cupboard or kitchen pantry, because it needs to be protected from light and humidity which cause it to degrade. Properly stored turmeric powder has a shelf life of around 2–3 years.
In conclusion, it’s not very difficult to dry turmeric rhizomes and make your own turmeric powder. It can be all be done using traditional, low-tech, sustainable methods without any electrical appliances if you so choose.
You might also like these other articles on turmeric plants:
- Growing Turmeric in Containers in Temperate Climates
- Growing Turmeric in the Ground in Temperate Climates
- U.S. Department of Health and Human Services, National Institutes of Health, National Cancer Institute – NCIthesuaus, Curcumin (Code C401)
- Food and Agriculture Organization of the United Nations (FAO), TURMERIC: Post-Production Management Organisation: AGST Prepared by Anne Plotto. Edited by François Mazaud, Alexandra Röttger, Katja SteffelLast reviewed:22/04/2004
- National Center for Biotechnology Information (2020). PubChem Compound Summary for CID 969516, Curcumin. Retrieved September 13, 2020 from https://pubchem.ncbi.nlm.nih.gov/compound/Curcumin.
- Chen, Zhipeng & Xia, Yao & Liao, Sen & Huang, Yingheng & Li, Yu & He, Yu & Tong, Zhangfa & Li, Bin. (2014). Thermal degradation kinetics study of curcumin with nonlinear methods. Food Chemistry. 155. 81–86. 10.1016/j.foodchem.2014.01.034.
- PRE & POST HARVEST PROCESSING OF TURMERIC, Senthamizh Selvan, R&D Food Technologist
Published on Jun 17, 2016 from https://www.slideshare.net/senthamizhselvan1481/turmeric-processing
- Farming India – Turmeric Cultivation in India, December 6, 2017