Hemp Grain Harvesting is generally performed by straight combining. Hemp will sprout easily so swathing is generally not recommended except for short varieties and in dry areas. Newer model combines generally handle the hemp harvest with few modifications. Standing hemp is harvested when the grain sample is in the range of 10 to 18% moisture. Drier seeds are susceptible to cracking. When hemp is mature, the bracts around the seed will dry up and the seed will be exposed. Early on, shattering is not a problem but as the plant starts to dry down and high winds are experienced, shattering can result.
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 to set and modify their combines. Most new combines work in hemp with few modifications. Cracked seed will result in oxidation that can turn the sample rancid. Newer combines have headers that can be raised high enough to harvest the majority of the crops with few problems. Growers report about 3 to 4 feet maximum height of the hemp crop should go into the combine. Over this height, wrapping and plugging will occur more often. 3 to 5 days after a killing frost the crop will likely be ready to combine as it dries down rapidly after the frost
Clean out the combine before harvest as residual grain can cause contamination that can result in downgrading, heavy dockage and possible product rejection. Draper headers are preferred because they have more room to give even feeding of the heads into the combine. Conventional headers also are used successfully. High moisture hemp will heat and spoil quickly. Harvest what your aeration or drying system can handle in a day. It is a good idea to turn the grain that is in aeration to prevent any hotspots or moisture build up that could start in “pockets” in the bin.
Start with canola settings for the initial combine settings of 550 rotor speed and 650 rpm for wind as a guideline. Adjust for each field. Bypass the chopper. Adjust the concave to minimize cracking of the seed coat. Operate grain augers full and at a slower speed to reduce cracking and de-hulling of the seed. 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. Machine modification takes time and planning to reduce problems during harvest. Watch for buildup of the fine dust in areas that build up heat like motors as it can cause fires.
Safe seed storage is below 10% moisture. It is suggested to use aeration fans on cold days to freeze the grain in the winter to help keep it fresh.
There are no grading or moisture standards but the industry is accepting 10% as being dry and the grain is safe for storage. Clean bushel weight is generally accepted at 44 pounds per bushel. 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 can have winter spoilage problems, so close monitoring of the bins is recommended. Some contracts want 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.
Sprouting in Hemp
Hemp grain can sprout very easily. This is an advantage in the spring for early and quick emergence after seeding. In fall, a prolonged period of high humidity and/or rainy weather can cause hemp seeds 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.
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.
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 standards have not been determined for hemp grain. It is expected that most buyers will be concerned about foreign material, seeds with adhering bracts, de-hulled, 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. 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 or further combine adjustments are required.
Health Canada regulations specify the grain must be stored in a secure and suitable location to which authorized persons only have access to.