Hemp is combined at a moisture content of 10 to 20% moisture. The majority of the moisture comes from broken plant material, immature seeds and seeds enclosed in bracts. Dockage will range from 10 to 20%. The wetter the sample, the more urgent the drying process is. Drying should begin within hours of harvest. Heated air grain dryers and aeration can be used for drying the seed down.
The industry has accepted 10% moisture as dry. A safer level is 8 or 9%. Percent moisture requirement should be checked with contractor.
Heated Air Dryers
A wide range of batch to continuous flow heated air dryers can be used.
- Hemp grain generally has a lot of bracts and broken plant parts that are higher in moisture than the grain. Once drying begins these plant parts dry quickly and the speed at which the grain dries also increases at the end of the drying cycle.
- Monitor grain dryer temperatures to ensure the seed and seed oil quality is not compromised. Overheating the seed can cause the seed to turn yellow and discount the oil quality.
- Use grain drying when seed moisture is over 13 or 14%
- Monitor the dryer operation closely. Batch and continuous flow dryers are the most commonly used. Augers should be run full and slow to prevent cracking of the grain.
- Use heat of 150 to 160 degrees F for the first ½ of the drying period and then use 120 to 130 degrees to finish off the drying.
- The grain requires frequent turning to avoid the development of hot spots.
- 9% or less seed moisture is considered dry for long term storage.
- Aeration is used to reduce the moisture content by a few percentage points, or to hold the grain until a dryer is available.
- Use a full floor aeration system.
- Aeration is not effective when fall conditions are cool.
- Heaters have been used in combination with aeration fans. Care should be taken as the grain at the bottom of the bin can over dry which can lead to cracking and quality deterioration.
- Turn the grain to prevent pockets or columns from forming which will harbor mold, spoilage, etc.
- For hemp in long-term storage, aeration can also be used in the fall when the weather is cold enough to freeze the grain. Freezing the grain maintains the quality, reduces the chance of spoilage and maintains a fresh quality for a longer shelf life.
- Many producers will turn the fan on two or three times during the winter to ensure it is frozen and to prevent moisture migration in the bin.
Aeration drying with and without a heater requires good ventilation at the top of the bin. During the drying process the roof will be cold and if there is inadequate ventilation the warm, moisture laden air will develop condensation on the inside of the roof. This moisture will then move down the sides of the bin and can lead to spoilage and mold buildup on the sides. Check for these conditions before emptying the bin because the mold buildup can fall into the grain during the emptying process and contaminate the entire bin.