The Issue of Dark Color in Ethanol Extracts
One of our potential customers recently asked us how to remove dark color from their ethanol extracts. They were getting dark extracts and were wondering about their options to make them look better. The oil was coming from an ethanol extraction process.
As an illustration of how dark ethanol extracts can be, refer to the photo above. The sample on the left is an oil produced by supercritical CO2 extraction and diluted in ethanol. The sample on the right is oil produced by ethanol extraction. The deep green coloration in ethanol extracts is caused by chlorophyll and xanthophyll that are extracted in solution from the biomass.
The Ethanol Extraction Conundrum
If you extract hemp plant material with warm ethanol, pigments and waxes will be co-extracted. These pigments typically taste bad and give a poor-quality appearance to the oil. Rotary evaporators (rotovaps) or stills are typically used to remove the ethanol, but the pigments, waxes, and poor-quality elements remain in the extract.
To minimize the extraction of non-active compounds, some people use extremely cold ethanol chilled to below -20°C. The most common cold ethanol extraction is the quick wash ethanol (QWET) method. Chilling the ethanol has the effect of lessening the solvent’s hydrophilic properties, thus minimizing the waxes and pigments that are extracted.
However, just as with any other chemical process, as the process gets colder, friction factors increase exponentially. At the same time, diffusion coefficients of the actives in the ethanol plummet. While the level of chlorophyll extraction and plant waxes is reduced, the absolute amount of active compounds extracted (cannabinoids, terpenes, etc.) also decreases greatly. In short, you get to choose: low recovery or high pigments.
Ethanol Is a Flammable Solvent
Another important thing to consider about ethanol is its high degree of flammability. You should familiarize yourself with the regulations around storage and use of ethanol before attempting to build a process based on large amounts of flammable liquid. You should always consider the infrastructure requirements and permit barriers to using large volumes of ethanol.
If you’re planning a large-scale ethanol extraction operation, you should read our post about things to consider when scaling up ethanol production.
The National Fire Protection Association has published NFPA 30 guidelines for explosion proof fixtures and infrastructure required. You can also find OSHA regulations here.
Removing Chlorophyll from Ethanol Extracts
When it comes to extracts, chlorophyll is an undesirable plant compound to say the least. The issue for ethanol extractors is that chlorophyll is highly soluble in ethanol and will likely find its way into an extract at some level. This makes it very difficult for ethanol extractors to produce a distillate that does not contain chlorophyll and other phytochemicals.
In terms of extract, residual chlorophyll can create a dark, undesirable color and potentially lesser flavor and aroma in an end product. So, removing chlorophyll from ethanol extracts is a crucial part of creating a desirable product, and there are many ways to do this.
One of the most common methods to remove chlorophyll from an extract is through activated charcoal; however, there are some drawbacks to this method and alternatives that could prove more desirable for extractors.
Activated Carbon and Its Drawbacks
Activated carbon (or activated charcoal) is one of the most popular options for removing chlorophyll and other unwanted non-active pigments in ethanol extracts. While activated carbon is quite effective at pigment removal, it is also very effective at removing active compounds. Due to the large pore diameter distribution and particle friability of activated carbon, it also results in a much smaller yield.
Another problem with activated carbon is its natural origin and the contamination that it carries. Activated carbon is typically derived from coconut shells or bitumen or wood. These products have significant ash content that contain heavy metals. When the carbon breaks up under use, these metals distribute throughout the oil as very small particles. They become very hard, if not impossible, to remove via filtration. Thus, they end up in your extracts.
The most overlooked aspect of using activated carbon however, is the solvation and dissolution of benzopyrenes into the extract. This class of compounds is produced as a consequence of the combustion of the coconut or bitumen. The Wikipedia entry for benzopyrene states the following:
Benzopyrenes are harmful because they form carcinogenic and mutagenic metabolites (such as (+)-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide from benzo[a]pyrene) which intercalate into DNA, interfering with transcription. They are considered pollutants and carcinogens.
How to Remove Chlorophyll With carbonX
So, care must be taken to use the right carbon. carbonX has been shown to solve the problems above because it is not a natural product, but is engineered by vapor depositing carbon onto a porous substrate.
The substrate will not break up, so the introduction of micron-sized ash content that is not filterable is unlikely. Furthermore, the material is washed so that extractables are not leaching from the materials into the extract.
We typically use carbonX in a couple different ways:
- You can use carbonX as a filter cake in conjunction with a DrainDroyd to dewax up to 5 liters of oil in 5 minutes.
- You can use carbonX dispersively by pouring it in, mixing, and then waiting for results. Then a DrainDroyd is used to filter the carbonX out of the extract.