Soil to Oil: The Agricultural Science Behind High-Quality Hemp Extracts

By James DuckerReviewed by Danielle Ellis, B.Sc.

Hemp refers to the botanical class of Cannabis sativa cultivars grown for industrial purposes and used throughout human history for paper, fabrics, and even medicines. Its first recorded use dates to 10,000 BC, when rope imprints on pottery were found in Northern China. More recently, there has been a surge in hemp production and its diverse applications.

From CBD oil to textiles and paper, hemp has many uses. However, it has gained popularity primarily due to cannabidiol, a non-intoxicating compound found in hemp with known therapeutic benefits desired by various industries such as health and wellness, skincare, and even pet care. The broad range of applications has made hemp production particularly attractive. For instance, European countries are now producing record amounts of hemp, estimated at 33,000 hectares in 2016 (Poniatowska et al. 2019).

The Science of Soil for Hemp Growth

The cultivation of hemp plants optimal for extracts requires specific soil quality and composition, which was reviewed in a 2020 study by Adesina et al. Hemp is a bio-accumulator, which means it absorbs substances from the soil it is planted in so that it can grow. The properties of the soil, therefore, directly affect its growth rate and overall resilience to the environment.

To optimize hemp growth, the soil must contain essential nutrients, be free from contaminants, and have a balanced pH level. Typically, hemp grows best in well-drained soil with a pH level between 6 and 7.5, which is slightly acidic to neutral. Additionally, hemp will prefer soil that is rich in organic matter and nutrients such as nitrogen, phosphorus, and potassium.

However, the study by Adesina et al. (2020) also mentions that research on optimal growth conditions has been limited to hemp fiber and hemp seed but rarely considers CBD hemp. Therefore, the conditions to optimize oil extract quality and quantity from hemp have yet to be considered in as much detail as other properties. Future research may benefit from broadening the scope of research to include other hemp properties of commercial use.  

Hemp Plant Genetics and Breeding

To supplement typical agronomical techniques of enhancing growth conditions, plant genetics, and selective breeding can also increase hemp productivity. For instance, if a producer is focusing on producing cannabidiol, the selective breeding of high CBD content, low THC levels, and improved terpene profiles in plants can increase the quality of hemp extracts. Additionally, genetic advancements have contributed to developing hemp strains with enhanced cannabinoid and terpene profiles, resulting in extracts with more consistent potency and targeted therapeutic properties.

Cultivators aiming to produce higher-quality oil extracts typically start by identifying parent plants with desired characteristics and then crossbreeding them to create offspring with a combination of those traits. Once harvested, cultivators can then evaluate the cannabinoid and terpene profiles of the plants, selecting those with the desired chemical composition. This process of selective breeding filters out plants of lesser value to focus on desired traits, ultimately producing hemp plants that yield extracts with targeted cannabinoid and terpene profiles.

Sustainable Farming Practices in Hemp Cultivation

To mitigate greenhouse gas emissions and reduce the dependence on water and energy, hemp cultivation often relies on organic farming techniques. Producers will rely on natural methods to maintain soil fertility and control pests rather than using synthetic fertilizers, pesticides, and genetically modified organisms. In turn, prioritizing soil health creates an environment that supports the growth of robust hemp plants with optimal cannabinoid and terpene profiles.

Sustainable practices also have a positive impact on the final oil extract quality. Specifically, organic methods preserve the integrity of the hemp plant and its extracts, ensuring a cleaner and purer product that aligns with consumer preferences for natural, environmentally friendly options. Therefore, avoiding chemical contaminants and promoting biodiversity may benefit producers, consumers, and the long-term production of high-quality hemp.  

Harvesting Hemp for Optimal Extracts

To obtain the best oil from hemp, understanding the effect of timing and harvest methods is key to getting the highest quality of extracts. A 2020 study by Marzocchi and Caboni in the Italian Journal of Food Science discusses the importance of timing the harvest of hemp. The study followed the fatty acid ratios as hemp matures and found that the ripening stage directly affects the quality of hemp seed oil.

Timing hemp harvesting to the right maturity stage is therefore important to ensure optimal cannabinoid and terpene profiles. Too early and the hemp may not have maximized its cannabinoid content; too late and the hemp may have higher THC levels, exceeding legal limits. Moreover, how plants are harvested also affects oil quality since physical damage to plants may affect the trichomes that contain cannabinoids and terpenes.

As a result, determining the perfect harvest window and the method of harvesting contributes to the quality of the product. It involves an empirical-based approach to assess the plant's chemical composition and physical attributes. One method is to measure the development and maturity of trichomes, which are the resinous structures on the plant's surface containing cannabinoids and terpenes. Visual inspection of trichomes under a microscope can help inform the harvest time based on the color and transparency of the trichome heads.

Another method to determine whether hemp is suitable for harvest involves testing plant samples for cannabinoid and THC levels. Although this may be more time and resource-intensive, it may track plant maturity more closely than visual inspection. Nevertheless, these monitoring methods allow cultivators to maximize the quality of extracts by harvesting the hemp plants at the peak of cannabinoid and terpene production.

The Extraction Process: Science and Techniques

Once hemp is harvested, several methods exist to extract the oil. Extraction can be done by passing supercritical CO₂, which is CO₂ in a fluid state, through the plant to extract all biologically active components. This form of extraction is an efficient process providing high product purity without residual solvents.

Ethanol extraction is an alternative method, which was reviewed in a study by Addo et al. (2022). Also referred to as the Soxhlet technique, ethanol is boiled, condensed, and cooled before warm ethanol is used to soak hemp material. This technique is often used since it maximizes the sample-to-solvent ratio and has a faster extraction time than CO₂ extraction or other methods, such as oil extraction.

Analytical testing methods are used to test the purity and content of extracted oil, including high-performance liquid chromatography (HPLC) and gas chromatography (GC). These methods are commonly used to measure cannabinoid and terpene profiles but also help identify contaminants such as pesticides, heavy metals, and residual solvents, which can be harmful to consumers. Testing from producers as well as third parties is considered crucial to verify product quality and safety, which in turn can instill consumer confidence and promote transparency in the hemp extract industry.