Plant descriptions:
Vernicia fordii is a shrub or tree growing up to 15 metres tall. The straight bole can be 25cm in diameter. The plant is evergreen in suitable climates, but can lose its leaves in areas with cold or dry seasons. In Vietnam, the tree is often cultivated in center & northern of Vietnam for the valuable oil obtained from its seeds.
The tung tree grows quickly. It begins to yield a crop from its third year, and approaches full production from year five onwards. The tree lives for about 30 years. The crown of the tree develops horizontally and has dense green foliage. The bark of the tree is smooth and grey..
The tree flowers in March-April and harvests fruit in September-October every year
The fruit of the tung tree is usually called a nut, although technically it is not. It is about the size of a tomato. The fruits grow in clusters, each yielding four or five nuts. Each nut contains three to five seeds which are similar in size and shape to a brazil nut. It is from these seeds that the oil is extracted. Each seed yields about 20% oil. When ripe, the nuts fall from the tree and are collected on the ground.
The word ‘Tung’ is Chinese for heart and refers the the heart shaped leaves of the tung tree.
How Tung Oil is produced
Traditionally, the fruits are collected when ripe, placed in heaps and covered with straw or grass. The fruit pulp is allowed to rot until the seeds can be easily removed. The seeds are roasted for a short time in shallow iron pans then crushed in a mill. The crushed mass is then thoroughly steamed and subsequently the fluid is pressed out of the cake yielding commercial wood oil.
In modern processing, hulling of fruits is done by hand or mechanically. The seeds are then dried and shelled mechanically, after which the kernels are ground with some shell added to facilitate oil extraction. Cold-expression is done in screw presses yielding a clear, light-coloured oil.
Tung Oil specifications:
Items |
Specifications |
Results |
Apprence |
Transparent or slightly turbid yellow liquid with inherent tung oil odor |
Transparent or slightly turbid yellow liquid with inherent tung oil odor |
Color (gardner) |
8.0 max |
7.5 |
Specific gravity (20°C) |
0.935 – 0.940 |
0.9387 |
Refractive index (20°C) |
1.516 – 1.555 |
1.5200 |
Iodine value(WIJS) |
163 – 173 |
166,5 |
Saponification value |
190 – 196 |
192,9 |
Moisture & Impurities |
0.1% max |
0.02 |
Free fatty acid |
6.0% max |
2,2 |
Worstall’s heat test |
7.5 minutes max |
7’ 05’’ |
Beta Tung oil test |
No crystalline precipitate |
Negative (no crystallization) |
Uses:
The seeds contain 14 – 20% of a quick-drying oil, called ‘Tung oil’. The oil is used traditionally in the manufacture of paints and Chinese black ink; for waterproofing cloth and paper; caulking and painting ships; and as a lamp oil. It was also formerly used for insulating electric wires. Currently, its main use is in the production of paints and inks,. Teak oil which is sold for maintaining fine furniture is usually refined tung oil.
Developments in environmental and health regulations have led to an increasing use of tung oil to line containers for food, beverages and medicines with an insulating coating. The main fatty acid of the oil is alpha-eleostearic acid . In eleostearic acid, the 3 double bonds are conjugated making them highly reactive. Under the influence of light or catalysts such as sulphur and iodine, alpha-eleostearic acid converts to beta-eleostearic acid, which is even more reactive and spontaneously polymerizes into a solid mass. The fatty acid composition of the oil is: α-eleostearic acid 75 – 80%, palmitic acid 4%, stearic acid about 1% and oleic acid 15%.
Traditionally, the fruits are collected when still green, placed in heaps and covered with straw or grass. The fruit pulp is allowed to rot until the seeds can be easily removed. The seeds are then crushed in a mill and roasted for a short time in shallow iron pans. The crushed mass is then thoroughly steamed and subsequently the fluid is pressed out of the cake yielding commercial wood oil.
In modern processing, hulling of fruits is done by hand or mechanically. The seeds are then dried and shelled mechanically, after which the kernels are ground with some shell added to facilitate oil extraction. Cold-expression is done in screw presses yielding a clear, light-coloured oil.