Grain Harvest

Combining is possible any time after the combined sample is 25% Moisture content or below. Generally hemp will be one of the later crops to be harvested. When the hemp is ready to combine, the seed will become exposed and start to push out of the bracts that hold it. Early on shattering is not a problem but as the plant starts to dry down and high winds are experienced, shattering can result.

Growers have found the optimum moisture level is in the 12 to 20% moisture range for grain harvest.

There is no grading or moisture standards but the industry is accepting 10% as being dry and the grain is safe for storage. Conversion tables for use with model 919/3.5 and 393/3.5 Labtronic moisture meters are found on the Canadian Grain Commission website. Hemp has had winter spoilage problems so close monitoring of the bins is recommended. Some contracts want the hemp grain at a lower moisture level so it is important to check your delivery contract requirements.

Maximum heated air drying temperatures to maintain grain oil and meal quality or seed viability are not known. Growers should err on the side of caution and use low plenum temperatures in heated air dryers. Air flow through hemp grain is relatively easy because of the seed size, the stem pieces and leaves. Many times the grain will be dry but the stems and leaves cause the sample to test tough. The stem pieces, leaves and trash can build up in driers and cause a potential fire hazard. Close monitoring is recommended.

Unheated air drying (aeration) is an option for drying hemp but consider the crop will often be combined late in the season when temperatures are cooler and unheated air drying is slow with marginal success. When using unheated air it is often wise to remove a few truckloads of grain to “turn” the bin to prevent hotspots from forming causing spoilage. Hotspots can occur in a matter of a very few days. When using aeration watch for excessive condensation on the roof which will run down the roof and side of bin causing spoilage.

Drying due to the presence of green material should commence immediately after combining to ensure quality remains high.

Hemp has a short storage life. Two or three years has been found to be the maximum shelf life when kept in storage. Processors like fresh hemp grain so that quality is maintained. The oil in hemp oxidizes in storage and taste qualities become altered. After grain processing the only other market is for bird seed, however the market price is about one-third.

Prevention and control of insects and mites in farm stored grain
Grain Drying and Storage of Damp Grain

 

Sprouting in Hemp

Hemp grain can sprout very easily. This is an advantage in the spring for early and quick emergence after seeding.

In the fall a prolonged period of high humidity and/or rainy weather can cause hemp seeds in the head to sprout in the standing crop. This can affect quality. Once the seed coat is cracked, the nut is subject to oxidization which creates quality concerns in regards to taste and storage.

Sprouted Seeds

It is suggested that if sprouting does occur that it be binned separately. This allows you and the processor to work with the samples to obtain the best use for the grain without affecting a larger lot.

Some of the shorter varieties or crops have been swathed in the past. Rain and humidity conditions do not need to last long before there would be sprouting in the swath. Swathing should be done with an eye on the weather to reduce this risk.

Grain Cleaning:

Hemp grain needs to be cleaned to rigorous standards for food processing. Conventional seed cleaning equipment should be able to deal with most foreign material or weed seed problems. Wild buckwheat and volunteer barley may be difficult to remove. Of particular concern in cleaning will be seeds to which the floral bracts adhere, or other hemp leaf or flower fragments. These may contain THC which could contaminate the oil when it is extracted (THC is not present in the seeds themselves). Most of the bracts are easily removed when the grain is dry. Contact contracting companies about cleaning requirements. Licensed facilities must be used.

Mature hemp seeds have dark markings. Frozen or immature seeds have a colorless light brown seed coat and must be removed in the cleaning process.

Grading

Grading standards have not been determined for hemp grain. It is expected that most buyers will be concerned about foreign material, seeds with adhering bracts, dehulled, cracked or otherwise damaged seeds, and off-type crop or weed seeds. Check with the market contractor/processor for quality requirements.

Peroxide level is a grading factor used by the industry. Peroxide values are a measure of rancidity that happens in the sample. Industrial hemp processors prefer a grain sample with a peroxide value under a value of 2 meg/kg. Table 7 illustrates peroxide values. The USO sample was combined at a low moisture content of 10%. The Alyssa sample was combined at 17% moisture. The peroxide levels are quite different with the USO sample on the threshold of not being accepted by the industry for processing. Table 7 suggests that because the USO sample was combined so much dryer there was probably more cracking of the grain. Once the seed coat is cracked, the nut is exposed to the air and oxidation can occur. This oxidization is the cause of rancidity. Adjustments maybe could be made to reduce the seed injury or perhaps the crop needs to be combined at higher moisture levels. More research is required.

 

Combining

Producers have invested considerable time and money to adapt and develop harvesting systems that work in hemp. Most types of combines have now been successfully used in hemp. New growers need to be prepared to invest time and money to learn and modify their combines.

The best approach for harvesting grain appears to be direct combining when moisture content is between 12 to 20% or when shelling becomes evident. The header cutter bar should be operated at a height that cuts off approximately the top half to one third of the crop. Operators have found that trying to cut more than 3-4 feet causes wrapping problems in the combine. New combines manufactured in the past 5 years are working in hemp with minimal modifications.

Some modifications that have been made to combines include covering all shafts, bearings and wires that might allow fibre to catch or wrap on the machine. Hemp is straight combined. Auger style and draper headers have been used successfully. If producers have a choice a draper header is used as it has more room for the stalks and feeding is often smoother. In most machines, the feeder housing is narrowed at the bottom to force the crop up the middle of the machine, keeping it away from the edges where the bearings are located. Some machines need an endless rubber matt to replace the feeder chain. Modifications have been made to some of the rotors of rotary combines. Machine modification takes time and planning to reduce problems during harvest.

Drying capacity is required for hemp production. The green bracts, leaf material and hurd in the grain sample means the crop needs to be dried quickly. It is recommended to only combine in a day the amount that can be dried before the next day.

Health Canada regulations specify the grain must be stored in a secure and suitable location to which authorized persons only have access to.