It pays to calculate grain shrinkage
GROWERS can avoid grain-drying and moisture-loss charges by having the correct facilities on farm, says John McArthur of Mecmar Driers.
When grain is accepted by merchants at a higher-than-contracted moisture content, the weight loss due to drying must be calculated. This enables the actual value of the grain to be worked out.
The loss in weight during drying is known as water shrinkage. It occurs when grain is dried, whether in the field or mechanically. The weight of dried grain may be calculated using shrinkage factors or the HGCA moisture calculator.
Shrinkage tables can be applied to all combinable crops – they are not influenced by crop type. But remember, there is a larger percentage reduction in weight for any given percentage reduction in moisture content.
For example, to determine the final weight of 18t wheat of 74kg/hal specific weight at 20% moisture content when dried and cooled to a final moisture of 15%, calculate the following:
- Look up the factor in the HGCA Final Weight of 1t after drying (kg) the intersection between the initial and final moisture contents – 941.2 kg
- Convert the figure to tonnes (divide by 1000) – 0.9412 tonnes
- Multiply the wet weight by the factor – 18 x 0.9412
- Answer – you are left with 16.938 tonnes at 15%
This demonstrates that for a 5% reduction in moisture content you actually see a 5.9% reduction in weight. Total shrinkage may then be calculated by adding the water shrinkage to handling losses during the drying process.
Research by the United States Department of Agriculture shows that on-farm handling losses can be anywhere between 0.22-1.71% and commercial installation handling losses range between 0.64-1.33%.
How these figures translate to UK farming practises is uncertain. But being able to calculate total shrinkage is one of the first steps in constructing an economic case for on-farm grain drying.
