Yield Testing
At least 2 Sub samples of between 150g and 200g are accurately weighed off. As these form the basis of all percentage calculations it is essential that no vegetable matter impurities or fibre is lost. The sub samples are then scoured in hot water and detergent, where the wool grease, suint (dried sweat), dirt and dust are removed. The sub samples are placed in tarred drying cans spin-dried to remove any excess water and then dried at 105 degrees, until no moisture remains in the samples.
Certain residual impurities, such as VM remain in the wool and must be measured. The percentage and type of vegetable matter present has an effect on commercial processing. A 40g specimen is weighed from each sub sample and dissolved in boiling 10% caustic soda. After 3 minutes only the alkali insoluble impurities remain.
These insoluble's are filtered out of the caustic solution, rinsed, dried and weighed. The total mass of the alkali insoluble matter is expressed as a percentage of the 40g test specimen. It forms an important part in the calculations of Wool Base and Vegetable Matter Base. Hard Heads and Twigs are calculated separately.
Other impurities remaining in the scoured sample are very small amounts of mineral matter and fatty residues. The percentage of ash content is determined from a 10g test specimen of the dried sub sample.
The test specimen is incinerated at a temperature of 780 degrees, or measured by Near- InfraRed Spectrophotometry.
The level of fatty matter is determined by ethyl alcohol extraction using soxhlet apparatus. A 10g test specimen is washed in ethyl alcohol which dissolved any fatty matter and transfers it to the soxhlet flask. After 21 cycles the ethyl alcohol is evaporated, leaving the fatty residue which is weighed and expressed as a percentage, or measured by Near-InfraRed Spectrophotometry.
At each stage of the testing process these values recorded. The system examines if the differences between the sub sample results of a test, are within specified tolerances. If not, additional sub samples are tested.
A certificate is issued showing the WoolBase (WB)and Vegetable Matter Base (VMB) obtained from the above process. Additional information is also given on the certificate.
