So yesterday I did my fourth run using this method, but I made several adaptations to refine the technique. I wanted to update the procedure for anyone who might be following along.
This time I stowed the flask and beaker in the freezer for 2 hours before starting the cooling bath. The extra step helps to prevent possible fracture by avoiding the extreme temperature swing.
At the end of the cooling bath, I left the flask submerged for another 15 minutes with the stirring plate off, to ensure all water had fully crystallized. I ended up with what looked
like more ice than last run, though admittedly I should have measured before the adaptation. Differences (if at all) in the end product are negligible, but I want to ensure there is positively no water in my absolutes. If nothing else, the extra 15 minutes give me peace of mind.
After the cooling bath, I immediately filtered out the ice so it wouldn't melt in the butane and reintroduce water to the solution. To do this, I needed two measuring cups: Measuring cup #1 is used to filter ice and plant material from butane. Measuring cup #2 is used to pour hot ethanol into measuring cup #1. I could bring the pot outside, but I'm paranoid about static discharge so I'm trying to use as little metal as possible.
Due to adhesion, any surface the solution touches will be left with a film of solvent which will quickly evaporate and leave essential oils stuck to that surface. The fewer surfaces the solution comes in contact with, the greater the return. The order of solution transfer goes: flask > measuring cup #1 > parchment baking cups.
During the cold ethanol precipitation wash, 4 hours in an average household freezer is sufficient time for all fats/waxes to coagulate and separate from the ethanol. There was just as much precipitate after only 4 hours in the freezer; 18 hours was overkill to say the least...
I found 1.5-2 mL of ethanol per gram of starting material to be a perfect ratio for my applications. Yesterday I ran 32 grams of buds and trim, yielding a little over 7 grams in return. I used 60 mL of ethanol, divided it up into four baking cups at 15 mL each and ended up with 1.7 grams of absolute a cup.
If there is excess water dissolved during extraction, multiple pulls can sometimes be beneficial when vacuum purging. Using a cooling bath freezes up any water dissolved with the butane, so heating to viscosity and pulling a second time is unnecessary. This time I pulled to -29.9 in Hg only once, and held it until the ethanol had completely boiled off. Again, the differences are negligible but at the very least it gives me peace of mind knowing I'm evaporating only what is necessary.
Here is the revised procedure:
- 1000 mL Pyrex wide mouth Erlenmeyer flask with polypropylene screw cap
- 2000 mL Pyrex heavy duty Griffin beaker
- two standard size Pyrex measuring cups
- butane (Colibri, Colton, David Ross, Dunhill, Lucienne, Newport, Sarome, Unilight)
- 95-100% undenatured ethanol (16 fl oz)
- acetone (32 fl oz)
- dry ice (10 lbs)
- protective gloves (natural or latex only)
- a stove top
- a freezer
- a pot
- a drill
- 1/8" and 3/16” drill bits
- a rubber band
- No. 4 unbleached coffee filters
- parchment baking cups
- two stage vacuum pump and chamber
- magnetic stirring plate and PTFE stir bar
- ABSOLUTELY NO SMOKING
- always have a fire extinguisher at the ready
- always setup outside, never spray or evaporate butane indoors
- keep the butane away from any/all possible sources of ignition
- take precautionary measures to avoid static discharge, no synthetic clothing
- immediately wipe up any accidental spills or spray, change clothing if necessary.
- never use fans to pull, only to push butane vapors away
. Leave butane in the freezer for at least 4 hours; it needs to maintain a temperature well below 30.2° F in order to remain in a liquid state.2
. Break apart flowers to 1/4" pieces and load up the Erlenmeyer flask, be sure to drop a PTFE stir bar in first. Screw on the polypropylene cap and let the flask and Griffin beaker chill in the freezer for 2 hours. 3
. Remove the the flask from the freezer, place it in the beaker so it’s sitting on the bottom and unscrew the cap. 4
. Crush up the dry ice and pour enough into the beaker to bury at least half of the flask. Pour acetone into the beaker in 50 mL increments until a slushy/slurry consistency is reached.5
. Drill a 1/8" hole in the polypropylene screw cap for butane injection, and a 3/16” hole for ventilation. 6
. Take one unbleached No. 4 coffee filter, place it in the top of Pyrex measuring cup #1 and secure with a rubber band.7
. Using Pyrex measuring cup #2, measure 1.5-2 mL of 95% undenatured ethanol per gram of flowers and pour it into the pot.The next four steps are by far the most dangerous, please refer to the Safety Precautions*Soak
8. Screw the cap onto the flask, put on protective gloves and get butane from the freezer. Without removing the flask from the cooling bath, carefully inject enough butane to submerge the flowers. Turn on the magnetic stirring plate, let it run at 750 rpm and monitor discoloration.
Butane is fractionally soluble in water. If it gets cold enough (below 32 °F) any water that is dissolved with butane turns to ice. During the cooling bath soak, due to extreme temperatures (-109.3 °F), water acquired by butane from moisture that may be left in buds and/or trim (including chlorophyll) will freeze up for easy filtering.9
. After 30 minutes (or once desired consistency is reached) turn off the stirring plate. Leave the flask in the cooling bath for another 15 minutes to ensure all the water has fully crystallized.10
. Put on protective gloves, carefully remove the flask from the cooling bath, unscrew the cap and pour the solution into measuring cup #1 through the secured coffee filter. Remove the filter and squeeze any extra solution out of the flowers.
Prior to disposal, be sure the filter/flowers have adequately dried to ensure all residual butane has evaporated. It’s an easy way to avoid inadvertently introducing butane vapors indoors. 11
. Go inside, be sure not bring a draft of butane vapor into the house; walk around to a separate entrance. Place the pot of ethanol on the stove and bring it to a boil (172.4 °F). Remove from heat, pour the ethanol back into measuring cup #2 and bring it outside.Wash12
. Monitor measuring cup #1. As soon as one third of the butane has been reduced, immediately (but carefully) pour the hot ethanol from measuring cup #2 into measuring cup #1.
The hot ethanol will help the cold butane exceed 30.2° F and boil off, leaving the essential oils behind. Because of the ethanol, phenolic resins remain dissolved and will not solidify to trap any butane gas in bubbles. Once all activity and bubbling has ceased, all butane has been fully purged.
When using non-polar solvents to extract essential oils, non-polar fats and waxes are extracted too. Ethanol is polar and washes essential oils clean, leaving non-polar fats and waxes in suspension for easy filtering.13
. Stow the measuring cup in the freezer for at least 4 hours to ensure all of the fats and waxes have coagulated.14
. Take the measuring cup out of the freezer, lay out parchment baking cups and get another unbleached coffee filter. Filter the precipitated fats and waxes out of the ethanol solution into the baking cups, 15 mL each.Purge15
. Place four baking cups in the vacuum chamber, turn on the pump and evacuate down to -29.9 in. Hg. After the ethanol completely boils off, continue to pull until there is no visible reaction. Once there is absolutely no activity, close the pressure gauge valve, disconnect the hose from the pump and turn it off. Remove the baking cups and enjoy!