By Acayo Christine Gloria, Media and Communication officer
The demand for sesame oil on both the local and international markets is increasing day by day especially by the Middle East and Asian markets. Its production however is still unreliable because Uganda rather exports sesame in seed form other than as refined oil and this is mainly due to the inefficient manual harvesting process required to extract the oil. Due to its low productivity, sesame oil ranks only ninth among the top thirteen oil seed crops which make up 90% of the world production of edible oil, according to the International Crops Research Institute for the Semi-Arid Tropics. Sesame oil comes in three types that are; refined sesame oil produced from unroasted sesame seed, roasted sesame oil produced from roasted sesame seed and small mill sesame oil which are produced from roasted dehulled sesame seed.
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Uganda is the 5th largest producer of sesame commonly known as ‘Simsim’ in the world and the 2nd largest in Africa. There are mainly 3 types of sesame that is white sesame, black sesame and brown sesame although in Uganda, it is the white and brown types that are grown with the SERRA and Sesi-1 species dominating. It is estimated that Uganda produces about 170,000 metric tons of sesame annually.
The low productivity of sesame oil in Uganda is mainly attributed to low levels of mechanization of sesame farms that make it hard to produce at a commercial level. In addition, threshing and drying seeds on bare ground mixes the seeds with soil and this makes it difficult to separate as the seeds are equally very small. This leads to low qualities and losses in the long run as buyers do not want to purchase seeds that are mixed with soil and offer very low prices for such produce.
In Uganda, sesame is grown in mainly two seasons; March-April and August-September. Sesame plants grow up to heights of 20-60 inches depending on the growing season and seeds should be planted between 0.75-1.5 inches deep. It thrives best in well drained fertile soils of medium texture and neutral pH-low tolerance for salt. Because of its extensive system of feeder roots, sesame is very drought resistant.
Harvesting should be done between June and July for the first season and November-December for the second season. It is important to harvest when the seeds are very dry as this makes storage and extraction of oil easy. Seeds should be stored in a very dry room with moisture content of less than 6% as moist conditions can cause the oil in seeds to heat and become rancid. A fully dried up seed contains about 50-55% oil.
To minimize damage and loss, great care should be taken during harvesting as damaged seeds have a negative effect on cost, quality and quantity of oil. Plant stalks are cut, bundled and laid vertically with cut ends down on wooden racks for 4-6 days so that they can dry followed by threshing and shaking over a cloth to release the seeds. The seeds are then collected and winnowed to remove the chaff and dirt.
Extraction of the oil
The extraction of sesame oil in Uganda is mainly done traditionally using a mortar and pestle. After harvesting, seeds are washed (this is to remove the soil that may have been collected), sieved and left to dry. The seeds are then poured into a mortar in potions and pounded until oil starts to collect. This is repeated until most of the oil is exhausted.
The residue left behind is normally used to prepare local meals cooked with either smoked fish or vegetables and in some cases used as animal feed.
The modern extraction methods used mainly in the few sesame oil industries in the country such as Kahangi Estate Organic Products are the batch hydraulic press where seeds are pressed by hydraulic pressure to extract the oil and the continuous mechanical pressing where seeds are squeezed through a funnel-shaped outlet and oil is expressed by increasing pressures and solvent extraction which is common in China and India.
The three main stages involved in oil extraction are; the cold press-the oil obtained in this stage has a light color and smell and is of very good quality. The second stage pressing is done with the sesame residue under high pressure which extracts a deep brown oil that should be refined to make it suitable for consumption. The third stage pressing involves subjecting the residue left after the second stage to more pressure to extract oil. The oil got at this stage is however of very low quality and is used for non-edible purposes such as making insecticides, paint and cosmetics among others.
Importance of sesame oil
- Sesame oil acts as a stimulus to liver function
- Seeds contain vitamin E that help to nourish the skin
- It acts as an antioxidant that helps to fight cancer cells
- The oil suppresses the development of hypertension
- Refined sesame oil is used to fry food
- Seeds are equally used as toppings on baked products such as buns
- It is an ingredient in making soaps, paint and cosmetics
The price of sesame oil has been rising gradually over the years due to its increasing demand both locally and internationally. A 237ml bottle of toasted oil goes for 20,000/=, unrefined oil of 236ml is at 25,800/= while a 376ml bottle of small mill sesame oil is sold at 26,800/=.
Although the focus of government and most sesame farmers is not on sesame oil production, it is important for priority to be put for it to be taken on as a subsidy as this will assist the sesame oil industry to grow and remain competitive and also earn more domestic income for both the farmers and government because of its value addition. Farmers need to equally be well informed of the demand and supply gap so as to effectively compete in the market.