Kosher vegetable glycerin is an effective method for extracting cannabis concentrates directly from the plant material and produces a tasty medication that is easily ingested directly orally, or mixed with drinks and food.
Glycerin is a heavy, syrupy clear liquid sugar alcohol that has approximately 60% of the sweetness of sucrose, and about the same food value.
It is however not actually a true sugar and is often used as a sugar substitute, as diabetics are often able to use it without experienced the blood sugar rollercoaster they suffer with sucrose or other sugars.
Glycerin makes an extremely tasty and provocative cannabis tincture, that when made using cold extraction methods, is reminiscent of wild honey, as it preserves all the individual flavors, so that they dart off in all directions simultaneously.
Hot glycerin extraction also makes a tasty tincture, with the flavor more resembling a fine soup, where the individual flavors are married into one overall flavor. While not as whimsical and provocative as a cold extraction, it can be prepared start to finish in a couple days, where cold extractions take a minimum of 60 days and are commonly soaked for 120 days or longer.
Many of the provocative flavors and odors from cannabis are aromatic terpenes, and the reason that they are aromatic in the first place, is that they give off molecules at room temperature.
Heating speeds up the rate that the accompanying terpenoids and other aromatics are vaporized off, so many are collateral damage in a hot extraction and are lost.
The glycerin molecule is actually only a three carbon molecule chain, with three hydroxyl groups (OH) attached, and as hydroxyl groups are hydrophilic, glycerin is hygroscopic (absorbs water) and dissolves readily (miscible) in water.
It has a flash point of approximately 177C (351F), and a boiling point of 290 °C (554°F).
It is relatively non toxic. The MSDS tells us that the LD50 Oral rat dosage is 12,600 milligrams per kilogram of body weight, which is approximately 5.7 grams per pound of body weight, or 36 ounces for a 180 pound male.
By comparison, acute oral toxicity (LD50) Oral Rat for sucrose sugar is 29700 mg/kg and about 7060 mg/kg for ethyl (grain) alcohol.
At saturation, Glycerin only hold as 33% as much cannabis oil as the same volume of ethyl (grain) alcohol, so about three times more is required per dose.
To reach maximum saturation however, requires processing more than one batch of fresh material through the glycerin, because as the saturation level increases, the glycerin becomes less aggressive as a solvent and the partially dissolved cannabis boundary layer interface with the solvent is also no longer at full strength and as reactive.
To keep the reaction from slowing to a snails pace, or even stopping, some method must be used to keep removing this stagnant layer and refreshing the boundary between the solvent and resin.
In addition heat dramatically affects resin dissolution rates. The hotter it is, the faster it works, up to the point of overheating.
As glycerin is usually used as an oral med, we also need to consider decarboxylating the cannabinoids so that they are orally active.
If not in excess, some water solubles add to the flavor of a glycerin tincture, and taking all of the water out of the material before processing it, makes it frangible and prone to breaking into small fragments that may be hard to remove.
Let’s look at how these four variables can be manipulated to produce delicious and effective glycerin tinctures.
Drying and decarboxylation:
Plant material is typically dried to around 10/15% water content by weight for smoking and vaporizing purposes, which is low enough to make some delicious glycerin, but for those who prefer less water solubles in their glycerin tincture or wish to decarboxylate the material before extracting, you may add a drying and/or decarboxylation step.
To simply remove most of the remaining moisture, I place the plant material on a cookie sheet in a 200F oven and turn it, until it is frangible when I roll it between my finger and thumb.
At that point it is ready for extraction, but if you also wish to decarboxylate the plant material before making your tincture, you can then crank up the oven to 250F and after it stabilizes at the higher temperature, replace the plant material in the oven and hold it at temperature for approximately 30 minutes
That will add a roasted flavor to the tincture and many of the turpenoids will be lost, but it will decarboxylate approximately 70% of the existing carboxylic acids into their non acid orally active form.
An alternative to decarboxylating the material ahead of time, is to do it after the extraction is complete and the plant material has been filtered out. That eliminates the roasted flavor and preserves more of the turpennoids.
Elevating the temperature of the glycerin increases the rate of dissolution of the resins, especially if you raise the temperature high enough for the resins to be molten. THC, CBD and CBN are all molten at just under 180F, so we operate at that temperature.
The advantage of using as low a temperature as possible, is that fewer aromatic terpenoids are boiled off at that low a temperature, and it decarboxylates more slowly, so that the process doesn’t pass the peak of the decarboxylation curve and start down the other side toward low THC and high CBN. As previously noted, we can finish the decarboxylation later.
Keeping the boundary layer removed:
The boundary layer is the layer of partially reacted resin and dilute solvent that forms on the surface of the resin after the initial aggressive dissolution by the solvent. The solvent at that point is dilute, as is the resin concentration, so that the reaction slows or grinds to a halt.
To keep the reaction operating at a reasonable rate, we need to periodically or continuously remove that boundary layer, and there are four methods that I will present here.
The first is to stir. Simply stir gently and thoroughly with a wooden spoon
The second is to shake. Simply shake a jar of glycerin and plant material by hand regularly. A paint shaker would also work for this application.
The third is to tumble. Placing the jar of glycerin and plant material in a rock or photo film tumbler will keep the boundaries fresh. It is an effective and gentle way to speed up the process.
The forth is vibration. Placing jar of glycerin and plant material in a vibratory cartridge case cleaner, or other form of vibration, creates more shear energy that tumbling and will dissolve the material the fastest of any method we have tried thus far.