Hemp cultivation requires the adjustment of nitrogen content to the local soil conditions, and in Poland optimal concentration of fertilizer is in the range of 40–120 kg⋅ha⁻¹ [37,38]. The study of other authors has shown that treatment with phosphorus, nitrogen, and potassium reduces THC and CBD levels in the inflorescence leaves. Moreover, the highest content of cannabinoids occurs in the hemp upper shoots and branches and declines in older leaves [39,40]. Another author observed that differences in sowing density between the levels of 40, 80, and 120 kg⋅ha⁻¹ do not significantly affect hemp yield. On the other hand, increasing the nitrogen dose and the sowing density causes slight changes in fiber yields [37].

The experiment showed no effect of nitrogen fertilization and sowing density on the content of CBD and Δ⁹-THC, suggesting that the applied doses of nitrogen were not decisive for producing cannabinoids in chosen varieties. Moreover, the obtained results showed the excellent adaptation of selected fibrous hemp varieties to the weather conditions during the study.

According to Pacifici et al., (2017), there is very little information regarding the characteristics of cannabinoids in aqueous extracts prepared from hemp [33]. The first records of cannabinoid concentration in tea obtained from narcotic cannabis indicate a reduced and heterogeneous recovery of cannabinoids, especially of pharmacologically important Δ⁹-THC. Prepared aqueous hemp extracts are a source of cannabinoids with medical potential. However, to obtain a product with a specific cannabinoid content, access to high-quality, homogeneous plant material and a stable method of cannabinoid extraction are required. Water extracts are currently not a traditional preparation method that could be used for recreational use.

The first few works on water extracts focused on the practical effects of cannabis water extracts and not on their characteristics. Nevertheless, there are mentions of the psychotropic effect of cannabis water extracts and their analgesic or non-psychotropic effect, which was due to the low content of Δ⁹-THC in cannabis tea [41,42,43,44]. At the same time, alcoholic extracts are the most common forms of preparation of pharmaceutical extracts. Therefore, the influence of temperature and concentration of the applied aqueous ethanol solution was investigated.

In their studies evaluating the ¹H NMR spectrum of an aqueous cannabis extract, Politi et al., (2008) also recorded the absence of typical proton signals indicating the presence of Δ⁹-THC and Δ⁹-THCA, which suggests reduced extraction of psychoactive Δ⁹-THC in the aquatic environment [34]. At the same time, the absence of Δ⁹-THC in the aqueous extract obtained from the narcotic variety explains the lack of this cannabinoid in extracts obtained from typical fibrous cannabis varieties (Futura 75, KC Dora, and Tygra) with the Δ⁹-THC content in plants below 0.2%. Moreover, Politi et al., (2008) reported that the use of elevated temperature (heating and boiling for 3 min) during water extraction causes Δ⁹-THC acid decarboxylation and increases the extraction and dissolution of Δ⁹-THC in water [34]. A similar tendency was found with the use of fiber hemp. Water extraction at elevated temperature increases the Δ⁹-THC content in the extracts, related to the low Δ⁹-THC content in the plant material, but the changes were insignificant.

There is a growing interest in obtaining cannabinoid derivatives by a solvent-free method based on mechanical separation rather than extraction. The solvent-free extraction is due to the semi-fluidity of the cannabinoids, which allows them to be extracted by appropriate heating and pressure [34]. Ice water separation (“cold water extraction”) is assumed to be ideal for producing a high-quality ice hash or bubble hash. The method involves the mechanical separation of the cannabinoid-rich trichomes from the biomass using water or ice and an excitatory force. Cold-pressed marijuana or hemp oil is cooled, placed under high pressure, and crushed to press the hemp oil out of the biomass. The method maintains the desired terpenes, flavonoids, and cannabinoids, but the yield is relatively low. Cold-pressed hemp and hemp oil appear in wellness products such as tinctures and topical formulations.

As suggested by Pacifici et al., (2017), it should be considered that differences in the content of cannabinoids within the variety may result not only from the applied agrotechnical conditions but also from the heterogeneous recovery of cannabinoids [33]. Water is a poor solvent, so hemp-based water preparations are unsuitable for accurate dosing [25]. Additionally, the above theory could be confirmed by the analysis of CBD and Δ⁹-THC in plants, where agrotechnical conditions did not influence the composition of cannabinoids within the varieties. Use of water for the separation of cannabinoids needs further analysis. Recently, simple techniques to limit solvents have been revived. Hence the interest in cold water extraction is sometimes called ice water extraction or cold water extraction. Low temperatures and mixing eliminate the need for aggressive solvents, leading to a clean and solvent-free concentrate [45,46]. Coldwater extraction also produces terpenic products such as live resin and extractions with a high terpene spectrum.

Under hot, cold, or room temperature conditions, alcohol extraction is one of the most effective extraction methods for processing large batches of cannabis flowers [16,29,35]. The advantage of using ethanol extraction is its properties. The ethanol extraction process is less explosive and toxic compared to hydrocarbon extraction or supercritical extraction with CO₂. Much cheaper infrastructure, higher bandwidth, and simplicity of use are further advantages. Due to its bipolar properties, ethanol is ideal for extracting a wide range of cannabinoids, especially at lower temperatures, and other compounds such as aromatic cannabis terpenes. During the extraction with ethanol, a crude oil is produced in the first stage, containing almost all hemp derivatives. After further refining and purification, e-cigarette oil, gel capsules, edibles, tinctures, sublingual drops, and topical products are obtained. Ethanol can also be used for large-scale extraction based on column or flash chromatography. Ethanol has its limitations. It does not purify individual cannabinoids and is not suitable for terpenes.

The obtained results from three hemp varieties demonstrated that the water extraction of cannabinoids enabled the extraction of cannabidiol without the detectable presence of Δ⁹-THC. The application of ethanol for extraction increased the level of cannabinoid extraction. The content of cannabinoids was proportional to the increasing ethanol concentration, leading to the better extraction of CBD and Δ⁹-THC. Hemp producers are increasingly starting to use ethanol extraction methods. Extraction is safe, efficient, and effective. Ethanol is often used as a food preservative and is considered “generally safe” by the FDA. The hemp plant is soaked in ethanol to extract the cannabinoids. After extraction, the product undergoes a refining process that improves the purity of the product. Ethanol will remove unwanted compounds from substances, offering one of the best-tasting and cleanest concentrates available.

Ethanol is a very efficient solvent, used in a wide range of temperatures from sub-zero up to the boiling point. Ethanol has been used for botanical extraction for thousands of years. The ethanol solvent binds to the chlorophyll, making the product taste bitter and isolating cannabinoids, terpenes, and flavonoids. Extraction tincture with alcohol allows one to obtain honey tar oil. It requires an initial stage of heating the material to about 121 °C, which leads to decarboxylation. The material is soaked in water and placed in pure, high-percentage alcohol. After draining and removing the alcohol, a classic oil is obtained.

The CBD content found in the extract at the level of 1.945% to 2.622% after applying ultrasound differs from the CBD content found in industrial hemp grown in Europe. Brighenti et al., (2017) reported the presence of CBD in selected varieties of fibrous plants at a similar level from 2.2 mg/g to 4.6 mg/g. The Futura 75 variety was also assessed, with 3.2 mg/g CBD [31].

In the case of the prepared tinctures, Politi et al., (2008) reported an increase in cannabinoid content with an increase in the concentration of ethanol used. The analysis of the ¹H NMR spectrum in ethanol extracts prepared from Δ⁹-THC-rich cannabis and Δ⁹-THC-free varieties showed a high Δ⁹-THC content in the 80% tinctures obtained from Δ⁹-THC-rich types, but no signal corresponding to Δ⁹-THC in the Δ⁹-THC-free array [34].

The conducted research also demonstrated that the selected varieties of fibrous hemp Futura 75, KC Dora, and Tygra contained the content of Δ⁹-THC consistent with the Polish law. Glivar et al., (2020), in their research conducted in 2017–2018, found that the content of Δ⁹-THC and CBD may be affected by environmental conditions such as temperature and hydration and that a warmer and dry summer increased the range of cannabinoids [1]. The dependence of cannabinoids on environmental conditions may also explain why variations in CBD content were observed among cultivars with different requirements of seeding density and nitrogen fertilization. Other studies also indicate that using ultrasound and HPLC for the ethanol extraction of cannabinoids allows for the proper characterization of the cannabinoid profile in the plant material [1,31].

Hydrocarbon extraction based on propane, butane, or hexane has been used for many years for food extraction. Hydrocarbon extraction enables the extraction of a greater variety of terpenes from the hemp material than alcohol extraction. The preservation of the terpenes helps give the extract flavor and aroma [14,34]. The extraction of butane honey oil (BHO) is widely used in the food and perfume industries. The extraction method involves placing the cannabis in a container before spraying butane on the cannabis. Cannabinoids and butane are collected in another container. The mixture should then be allowed to evaporate, or a vacuum oven can be used to remove all butane from the variety. Extraction of BHO is dangerous due to the high flammability of the substance. THC levels when the BHO extraction method is used remain at around 80%.

Hydrocarbon extraction equipment is generally considered cheaper than CO₂ and ethanol extraction equipment, but hydrocarbon extraction does not necessarily yield CBD and THC. Butane is mainly used on the desired product, followed by propane and hexene, due to the difference in boiling points. Mixtures of hydrocarbons may also be used. The cannabinoid concentrate obtained under the influence of liquid butane contains terpenes and cannabinoids (THC, CBD, and other smaller cannabinoids), vegetable waxes, and lipids. It is subject to further refining, including dewaxing, centrifuging, and wintering. The final step removes the hydrocarbon solvent from the extract by degassing. The use of hydrocarbons helps maintain the strain’s flavor profile, and it is a quick process using different parts of the cannabis plant. The hydrocarbon is ideal for producing edible cannabinoid derivatives such as budder, butane hash oil (BHO), crumble, honeycomb, aggregate, resin and wax, topical products, edibles, e-cigarette cartridges, tinctures, and capsules.

Edible oils such as extra virgin olive oil, coconut oil, and butter are used on a small scale to extract fat-soluble cannabinoids by gently heating the decarboxylated cannabis flowers directly in the edible oil [15]. The resulting oil is much less powerful and has a shorter shelf life than other extraction methods. In the first stage, the plant material is heated, which enables the conversion of cannabinoids into more bioavailable forms, for example, CBDA into CBD and THCA into THC by decarboxylation or decarbonization (approx. 140 °C for 30 min or 120 °C for 60 min) [15,47]. The vegetable oil is then added and heated to 100 °C for 1–2 h, allowing the decarboxylated cannabinoids to bind to the fat molecules in the oil. The plant material is filtered out, leaving a vaporized cooking oil containing a mixture of vegetable oil, terpenes, waxes, cannabinoids, etc.

CO₂ extraction is a non-toxic, environmentally friendly method of separating cannabinoids from the cannabis plant, requiring precision equipment. It is also used in producing beer, coffee, fruit extracts, and tea. There are three main modifications: CO₂ extraction in supercritical, subcritical, and medium-critical states [34,35]. The former is assumed to be the gold standard of extraction. However, the need for specialized equipment and skilled personnel remains an issue, leading to limitations in implementing these methods as simple and easy-to-use techniques. Due to the above, no extraction with the use of CO₂ was undertaken in this study. Supercritical CO₂ is heated and passed through the cannabis buds to produce waxes and oils. Low extraction temperatures at very high pressure ensure pure oil extraction. Nearly 500 cannabis compounds can be obtained [14,34,35].

Subcritical CO₂ extraction proceeds at low temperatures and pressures, despite longer extraction times and lower yields than supercritical extraction, preserving the “full spectrum” of beneficial cannabis compounds (e.g., fine terpenes). Medium-critical CO₂ exists in ranges of temperature and pressure between subcritical and supercritical.

Isopropyl alcohol is required for this extraction method. The dried hemp flowers are soaked in alcohol and then gently shaken. Isopropyl removes hair from the plant. The mixture is strained into a vessel, and then the solvent is removed using a vacuum oven which keeps the temperature below 181 °C. Once the solvent has evaporated, the remaining substance is oil-rich in THC. A new patent involving a new extraction method that uses algorithmic extraction to manipulate temperatures to extract cannabinoids and terpenes without losing some of the plant’s properties was prepared by Curo Medical Ltd., which specializes in the delivery of cannabis in the form of pills or sublingual strips instead of traditional smoking, vaping and eating. All extracts must be appropriately stored and refrigerated to maintain durability and quality.