Hemp grown for the CBD will be harvested when CBD is highest and THC is still below the 0.3% threshold. Many growers look at the color of the trichomes to determine when to harvest. Monitoring THC and CBD levels should be the driving factor to determine harvest date. There is instability in hemp genetics, factor in monitoring cannabinoids when you are assessing cost of production.
Growers are using different technology to harvest their CBD hemp and harvest method will likely depend on the size of the operation. Hiring laborers to hand-harvest is a common method. Some growers are using mechanized harvesting. Growers in tobacco production states are using KIRPY harvesters. Growers that are producing at a large scale are using combines. Some growers are working with custom made equipment, like the Revolutionary Hemp Harvester.
Most processors are requiring that plants be dried prior to arriving at an extraction facility. In Kentucky, growers are using existing tobacco barns to hang and dry their hemp. There are mechanical drying machines that run forced air over the hemp and facilitate quick drying for those that cannot hang dry. If you plan to hang dry, check the load-bearing capacity of your structure.
After the plant material is dried, some processors require that they receive material in super sacks already chopped or pelletized, while other processors want hand shucked hemp material. Each processor will have their own specifications about how the material should be harvested, dried, and shipped to them.
Processors can differ greatly in how they extract CBD and other cannabinoids from the raw hemp. Alcohol, hydrocarbon, and supercritical CO2 are all common methods of extraction.
Winterization helps separate waxes and lipids from the crude oil. This is typically done by mixing crude oil and ethanol and then exposing the solution to sub-zero temperatures for a specific amount of time.
Distillation is used to purify the extract further.
Isolation is used to refine the distillate to a pure cannabinoid, in this case, cannabidiol (CBD).
Formulation is necessary to make CBD oil that has the correct concentration of CBD in the bottle. Different carrier oils are used and sometimes flavors are added.
There will be a loss at each step of the extraction and distillation process. More detailed explanations of each type of commercial extraction can be found here.