Vegetable glycerin (glycerol) extraction is an easy effective way to extract cannabis concentrates, and within the capability of most folks to perform. It can be as simple as soaking in a fruit jar for 90 days, or as complicated as using vibration, tumbling, stirring, and heat cycling for the more adventuresome brother or sister.
Vegetable glycerin tincture made with prime bud can be as tasty and whimsical as wild honey from local pollen when done cold. The provocative flavors darting off in all directions at the same time, are of course the terpene, terpenoid, and flavonoid solute in the glycerol, so older less aromatic material will be less tasty.
It is still a tasty soup, with the individual flavors married when extracted hot. Not as whimsical and tasty, but extraction time is shortened from 60 days minimum, commonly 120 days or longer, to only a couple.
We obtain our organic and Kosher vegetable glycerin from Glory Bee in Eugene Oregon. https://wholesale.glorybee.com/organic-liquid-vegetable-glycerin-17379-1
It is a thick syrupy, colorless complex sugar alcohol, with about the same food value a sucrose, but only about 60% as sweet. The following picture is the sucrose molecule, followed by the glycerol molecule.
As you can see, the glycerin molecule has only three carbons with hydrophilic OH hydroxyl groups attached, which makes it highly water soluble (miscible). It has a boiling point of 290C/554F, and an LD50 Rat dosage of 12,600 mg/Kg of body weight, or about 5.7 grams per pound of body weight.
Here is a link to Science Labs MSDS for glycerol: http://www.sciencelab.com/msds.php?msdsId=9927350
Its dielectric constant is 42.5, so it is more polar that Isopropanol, Ethanol, or Methanol, yet is less prone to pick up chlorophyll, we're guessing because of its slight negative charge and chlorophyll's slight positive charge from the magnesium ion.
Material selection and preparation have a big impact on the results. If you want tasty glycerin, you have to start with tasty material. We prefer to strip the fan leaves from our plants and hang them upside down for 5 to 7 days, or until the small stems just snap. At that point most of the water has been removed, but the material is still rife with monoterpenes and flavonoids.
Older drier material will produce more hashy flavors from the remaining Diterpenoids.
Cold extraction is accomplished by simply soaking the plant material in the glycerin. We break the buds up loosely by hand and pack into a canning jar loosely, before covering with about an inch of glycerine at ambient temperature.
Jar of leafy trim.
Every day we shake the jar, and store it in a dark cool place.
After a minimum of 60 days, more commonly 90 days, and sometimes 120 days or longer, the material is pressed to squeeze the glycerin from the plant material. I actually have a sample I squeezed after around four years, with a wonderfully delicate flavor.
There are a number of ways to press the glycerin out, but since we started with a simple cold extraction in a fruit jar, let’s also look at a simple method for pressing as well. The following picture shows a commercial potato ricer, which can handle a quart of material per load.
Commercial potato ricer from Hong's Restaurant Supply.
To press the glycerin out of the material, first place about a 12" square piece of about 200 thread count bed sheet over it and press it into the sieve to make a pocket. Dump the jar of glycerine and plant material into the pocket, guts, feathers, and all.
Press out the glycerine and save the plant material for a second run. More on second runs later.
Squeezing material wrapped in cloth from old bed sheet.
For larger quantities, I came up with this DIY press out of an $18 six ton bottle jack, a couple stainless dog dishes, and some scrap metal I picked up by the pound. I've also used this press for Cannabuttons, and will next equip it for pressing Rosin:
If you look close at the edge of the pans held in place by the jack, you will note that there are actually two pans there and the bag of material to be pressed is placed between them, so that only stainless is in contact with product.
The glycerin tincture pressed out of the bag is caught in the third pan underneath.
View of Glycerin Press platen
Sooooo, what if you don't have 60 to 120 plus days? What are the options?
A couple of options. One is to use heat to speed up the process, performing an extraction in a couple days, instead of 60+ days.
Another is to aggressively keep the boundary layer removed so that fresh solvent is in contact with full strength resin. When a solvent and a resin come in contact, a reaction occurs, but as it progresses, the solvent in contact with the resin becomes more saturated and therefore of lower strength.
Likewise the resin in contact with the solvent becomes partially dissolved and is no longer full strength either.
To keep the reaction going at maximum efficiency requires that we constantly remove the boundary layers. In the above extraction, we shook the jar once a day, but alternatives to that is using vibration or tumbling. We've used both to good effect and we'll be discussing it more later:
RCBS Vibratory shell case polisher.
We've run three half pint jars wrapped in news paper in the RCBS Vibratory shell case cleaner to good effect and will show samples later.
More common and popular is a tumbler. Here is one we use that handily tumbles a gallon of bud and glycerin:
Tumbler using gallon jar
We'll get to show and tell shortly, but first lets explore heat and heat cycling, in conjunction with agitation to keep the boundary layers refreshed.
We typically hot extract at 180F and do it in a fruit jar as well, though care is required to not break the jars. We use a Cussinard fondue pot full of canola oil with jar lids in the bottom to keep the jars elevated.
Here is a picture of material being processed and shows a metal spoon being used for stirring, but we have the best luck with a wooden spoon that can't accidentally tap the thermally stressed glass hard enough while stirring, to initiate a crack.
The thermometer is how we keep track of the solution temperature vis a vis the bath temperature.
Hot oil bath for cooking glycerin extractions.
We start out by placing the jar in the 180F oil and turning the thermostat up to 200F. We stir regularly and once the internal temperature of the jar reaches 180F, we turn the thermostat back down to 180F and continue to process and stir regularly for 30 minutes.
We then turn off the heat and let the jar cool down to ambient. Once it is at ambient, we again place it in the hot oil and repeat the process about five times total.
When done, we press it just like the cold extract, except that we do it hot. Careful to not burn yourself with the 180F oil or glycerin.
Flavoring glycerin tincture:
Aside from how tasty glycerin tinctures can be all by their lonesome, you can also add to that flavor with other additions.
We started by making a thin paste out of Bing Cherry and Blueberry raisins in a blender, using 1/2 cup of 190 proof ethanol to thin it out.
We then added a half measure of Japanese Gari, with a dash of Almond extract, and pureed it well.
Next we cooked it in a 180F hot oil bath until the alcohol was gone, before setting it aside to cool.
After adding two tablespoons of this concentrate to a 1/2 pint of infused glycerin tincture, we place the jar in the 180F oil bath and cook for 30 minutes while stirring regularly. When finished, we filter while still hot, with the worker bees sharing eating the spent flavoring material from the filter bag.
Sooo, which process to pick??? My suggestion is to try them all and pick the one that you like best, but here are some results to help you narrow it down.
The first is a comparison of the color density a 60 day cold extract and a 2 day hot cycling extract.
60 day cold extract versus 2 day hot cycle extract.
As you can see, the hot has considerably more color, begging the question of what happens to glycerin itself when you heat it to 160F.
The first sample below is virgin vegetable glycerin that has been heated to 160F seven times without any plant material present. The second a 60 day cold extract, the third a 90 day cold extract, and the last a 120 day cold extract.
Heat cycled virgin glycerin, 60, 90, and 120 day cold extract samples.
120 day cold, hot, and hot heat cycle.
Hot, shaken not stirred, hot heat cycled at 160F, cold vibrate, and hot vibrate plus 160F cycling.
Lastly lets talk about gleaning. As glycerin is limited in how much cannabis essential oil it can hold in solution, and extraction slows down as the concentration of solute builds, the "spent" plant material typically still has enough target elements left to justify a second and even sometimes a third extraction of the material.
We crumble the pressed pucks up by hand and run another cycle on them. Here is an example of a second pressing, which demonstrates how much material was still left.
2nd processing showing gleaned concentrate density