By David Karki
Corn marketed at the standard moisture content of 15.5% and 56 pounds per bushel typically contains 47.3 pounds of dry matter and 8.7 pounds of water. At harvest, a producer has to decide whether to sell (or even store) his corn at ‘as is’ moisture content or mechanically dry before taking it to the buyer. For proper storage, grain moisture content has to be reduced to acceptable levels. Corn at 15.5% can be stored up to six months, 14% up to 12 months and 13% for more than one year. Total weight loss while drying grain to desirable moisture levels is called ‘shrink’ and grain buyers usually take this into consideration to estimate how much actual grain they will have after it is dried down.
Moisture Shrink, Shrink Factor, and Total Shrink
MOISTURE SHRINK
Moisture shrink can be calculated by the following formula:
1 − [ (100 − Initial Moisture) ÷ (100 − Final Moisture) ] × 100%
For example: Corn with 25% initial moisture and 15.5% (final moisture) after drying has a moisture shrink of 11.24%
MOISTURE SHRINK FACTOR
Moisture Shrink Factor is determined as:
100 ÷ (100 − Final Moisture)
From the example above, water shrink is calculated as 1.18% for each point of moisture removed when the final moisture is 15.5%. Table 1 shows the moisture shrink factor when drying corn grain at different moistures.
Table 1. Moisture shrink factor when drying corn grain at different moistures.| Final Moisture Content (%) | Shrink Factor (% Shrink per point) |
|---|
| 15.5 | 1.18 |
| 15 | 1.18 |
| 14 | 1.16 |
| 13 | 1.15 |
| 12 | 1.14 |
| 11 | 1.13 |
| 10 | 1 |
TOTAL SHRINK
The total shrink accounts for both moisture shrink and handling loss. When shelled corn is dried from 25% to 15.5% total weight reduction is 11.24% of the original weight. When handling loss is added the total weight reduction would be greater than 11.24%. To estimate the total shrink or total weight loss grain buyers generally use a constant shrink factor which can range from 1.2% to 1.5%. The handling loss alone can range from 0.22 to 1.71% and the research shows that less than 1% handling loss is considered ‘reasonable’. This handling loss can vary depending on corn quality, drying method, and the handling throughout drying process. Generally, when the constant shrink factor increases, total handling loss also increases.
Source : sdstate.edu