Butane Honey Oil, or BHO, is the essential oil from the cannabis plant, extracted using n-Butane as a solvent. If it is extracted from fresh material, it is a Concrete, and if from cured material, it is an Oleoresin. A concrete or an oleoresin that has been winterized to remove the waxes, lipids, and fats, is known as an Absolute.
Butane Honey Oil extraction refers to the method used to extract the essential oils from cannabis, and there are multiple theories on the best way to accomplish this, as well as what material is best to use.
Perhaps the first question is why use a BHO technique to extract the resins, instead of just boiling the material in alcohol to get the greatest amount of extracted material?
The answer to that is that because butane is relatively non polar, it doesn’t extract the water solubles like chlorophyll and plant alkaloids. Butane produces one of the cleanest extractions, albeit typically at a lower yield than polar alcohol.
On average we have extracted about 18% oil by weight from bud, but as low as 5.7% absolute and as high as 25 absolute%.
The first wash will usually extract 75 to 80%, leaving the balance for the second after repacking the column. The second extraction will be more sedative and less heady. If you use a hand microscope, you can easily see when the trichome heads are gone and the stalks look like wet fur.
We’ve only tried a few processes here at the pharm, so I will cover only simple flow through columns, a thermos bottle, a pressurized system, and a closed loop one.
We currently use a closed loop system for BHO, and as I am covering that process on a separate thread named The Tepenator, where I will detail building our second generation automated system.
Prior to using our DIY closed loop system, we did our BHO extractions using single pass flow through packed columns, and experimented with a thermos and a simple pressurized system to soak at ambient temperature. I will cover simple columns and thermos bottles separately, as the techniques are different and I need to make some more pictures for the latter.
Before we discuss how to extract the essential oils from cannabis, let us talk about the plant material to be used. That immediately brings to mind the qualifying question, “What do you want to use it for?”
Oil that is to be vaporized, is normally treated differently than oil that is used orally or topically, because it doesn’t need to be decarboxylated. For cannabis concentrates to be orally and topically active, it does require that the THCA and CBDA be converted to THC and CBD, by a heating or drying process. I will cover that issue under a separate thread on Decarboxylation, so as to not clutter this post.
Besides the cannabinoids, which are Di-Terpene alcohols and di-alcohols (diol), there are also other terpenes in cannabis essential oils, which add to its smell, flavor, and medicinal entourage effect. Some of these terpenes are highly aromatic alcohols, phenols, ketones, aldehydes, ethers, and esters, which are aromatic because they freely give off molecules at even ambient temperatures.
Heating the plant material or the oil to decarboxylation temperatures will evaporate off most of these smaller aromatic Mono-Terpene and Sesqui-Terpene molecules, before the larger and heavier cannabis Di-Terpenes are affected. Decarboxylated oil is smoother to the taste, but basically tastes like hash, with the floral undertones gone.
Gone also are the medicinal and entourage effects from those terpenes. The price we pay for decarboxylation, so we shouldn’t decarboxylate casually, and should first consider the end use before picking the process.
One of our process limitations, is that though non polar, n-butane has slight water solubility. At 20C/68F, it is only 0.0325 percent by vol/vol, but not zero and is still enough to pickup undesirable water solubles. 1 liter, or 1000 ml X 0.0325 = 32.5 ml of water.
With water, comes water solubles, which includes chlorophyll and plant alkaloids, that detract from the taste, so the dance is to maintain the volatile terpenes, while studiously avoiding the water solubles.
Freezing the water is one method that works well, but it is important that the material be dry when it was frozen and that it is not exposed to high humidity while frozen, or ice will form over the trichomes, preventing their extraction.
Another method is to simply remove most of the water. This will produce pristine extractions, but doesn’t preserve the terpenes. If the material is to be decarboxylated anyway, that is of little concern, because we will lose them anyway.
We also have the issue of purging out the remaining butane, while preserving the terpenes. Again, there are a number of ways to do that, but I will address only a few of the ways that have worked for us here. Those are light heat, high heat, and thin film vacuum.
So, besides decarboxylation, what are some of the things to consider selecting a process and how should the plant material be prepared?
In our experience, for best flavor and taste, freshest material works best, whether it is fresh frozen material or dried. Older cured material loses the nuances of the floral undertones and just tastes like hash. That means that the degree of drying and curing is also critical, if your goal is to maintain maximum terpene content.
Oil from buds is tastier than oil from even sugar trim, because most of the terpenes are produced by the buds, and that is where they are the most plentiful. Tasty is usually not a word used to describe oil from fan leaves or stems, though effective may be.
The absolutely most flavorful BHO extract to me personally and to the test panels thus far, is fresh picked buds, that are immediately frozen to tie up the water, and extracted while still frozen. It produces an oil that abounds in whimsical flavors darting about and the word most often used to describe it by panel members, was the word “fresh.”
Next most flavorful, from a BHO standpoint, is material that has only been cured 5 to 7 days, and is at the small stem snap stage, where you might jar it if you were curing it to smoke.
Part of the formula is of course the degree and methods used to purge out the remaining butane. While there are a number of ways to do that as well, I will address only a few of the ways that have worked for us here. Those methods are low heat, high heat, and thin film vacuum.
Lastly, selecting a suitable butane source is a key step, in that all butane sources aren’t created equal. n-Butane (normal butane) is a simple alkane, with four carbon atoms linked together in a row, with the remaining possible carbon bonding sites taken up by hydrogen atoms.
The simple alkanes all are gaseous at room temperature and atmospheric pressure. They are removed from crude oil before it is further processed, by simple heating. The simplest is Methane, which is only on carbon and four hydrogen atoms, followed by Ethane with two carbons, Propane with three, and Butane with the four.
Pentane is the next simple alkane, the first to be liquid at room temperature and the first to have zero water solubility. From Pentane on, the simple alkanes are named from the Greek alphabet, and are Hexane, Heptane, Octane, etc, on through the light naphthas, oils, waxes, and asphalts.
The formula for all simple alkanes, is the number of carbon atoms times two, plus two, because each carbon atom has four possible bonding sites. A mnemonic device for remembering the first four alkanes, which were named before the Greek system was applied, is Mary Eats Peanut Butter.
After removal from the crude oil, the gases are typically de-sulfurized using steam and a catalytic reactive bed, and fractionally distilled into the four basic gases. As fractional distilling separates the gasses by specific gravity, the principal contaminants in n-Butane at that point, will be Iso-Butane, a branched molecule isomer of n-Butane, as well as n-Propane, and Cyclo-Propane, plus low levels of heavier, longer oleaginous alkane wax chains.
Neither of the butanes or propanes are particularly toxic at any sort of reasonable levels. The following for instance is taken from a typical MSDS sheet for n-Butane. The Rat LD-50 (50% dead) is 658000 mg/m3 4 hours. That is breathing a 65.8% pure butane atmosphere and asphixiating.
Section 11. Toxicological information for n-Butane; Diethyl; Freon 600; Liquefied petroleum gas; LPG; n-C4H10; Butanen; Butani; Methylethylmethane; UN 1011; UN 1075; A-17; Bu-Gas.
Carcinogenic effects No known significant effects or critical hazards.
Mutagenic effects No known significant effects or critical hazards.
Reproduction toxicity No known significant effects or critical hazards.
No specific information is available in our database regarding the other toxic effects of this material to humans.
Chronic effects on humans May cause damage to the following organs: central nervous system (CNS).
Other toxic effects onhumans
Butane LC50 Inhalation Vapor
Rat 658000 mg/m3 4 hours
Product/ingredient name Result Species Dose Exposure
Products of degradation: carbon oxides (CO, CO2) and water.
Section 12. Ecological information
Products of degradation :
Environmental fate : Not available.
Environmental hazards : No known significant effects or critical hazards.
Toxicity to the environment : Not available.
The MSDS LD-50s on Iso-Butane, Propane, Cyclo-Propane, and oleaginous waxes are as follows:
n-Propane; Dimethylmethane; Freon 290; Liquefied petroleum gas; Lpg; Propylhydride; R 290; C3H8; UN 1075; UN 1978; A-108; Hydrocarbon propellant. LC50 Inhalation Gas: Rat >800000 ppm 15 minutes
Cyclopropnane; Trimethylene; Trimethylene (cyclic); UN 1027; No LD-50 established;
Iso-Butane; 2-methyl-; Trimethylmethane; 1,1-Dimethylethane; 2-Methylpropane; isoC4H10; i-Butane; Isobutane mixtures; UN 1075; UN 1969; R 600a; tert-Butane; A 31;Methylpropane; Propane, 2-methyl-isobutane LC50 Inhalation Vapor Rat 658000 mg/m3 4 hours
Oleaginous Waxes- Paraffin, no notable toxicity or LD-50 available
n-Butane is used for any number of things, so it is processing beyond this point, or sharing storage tanks with other contaminated sources that may create health concerns. While n-Butane is non-toxic enough used as a food propellant, if it is to be used as a stove fuel, it will in most cases have an odorant added for leak detection, as n-Butane has only a very light sweet petroleum odor.
Ethyl Mercap is most often added for that purpose, and is the familiar rotten egg smell is detectable at the astonishing low concentration of under 3 parts per Billionth! Hexane (Gasoline) by comparison, has an odor threshold of around 30 parts per millionth, or about 10,000 times more is required for us to smell mercaptoethanol.
The MSDS for Ethyl Mercaptan shows 4420 ppm/4 hour(s) inhalation-rat LC50; 682 mg/kg oral-rat LD50, with the target organs being the central nervous system. Not super toxic, but tastes and smells of rotten eggs, so that point may be mute.
Butadiene may be added to stove fuel as well, and is of serious concern. While the following typical MSDS example shows relative low toxicity, take a look at the carcinogenic effects.
LD50 Oral Rat 5480 mg/kg -LC50 Inhalation Vapor Rat 285 g/m3 4 hours
LC50 Inhalation Vapor Rat 285000 mg/m3 4 hours
LC50 Inhalation Gas. Rat 128000 ppm 4 hours
Mutagenic effects No known significant effects or critical hazards.
Reproduction toxicity No known significant effects or critical hazards.
No specific information is available in our database regarding the other toxic effects of
this material to humans.
CARCINOGENIC EFFECTS: Classified 1 (Proven for humans.) by IARC, 1 (Known to
be human carcinogens.) by NTP, + (Proven.) by NIOSH, 1 (Proven for humans.) by
European Union. Classified A2 (Suspected for humans.) by ACGIH.
MUTAGENIC EFFECTS: Classified 2 by European Union.
May cause damage to the following organs: the reproductive system, mucous membranes, upper respiratory tract, skin, eyes, central nervous system (CNS).
n-Butane may also be further refined to increase its purity, or to make it suitable for use in butane lighters. R-600 Refrigerant and Instrument grade n-Butane are examples of higher purity n-Butane suitable for extractions, and are distributed by suppliers like Matheson and Airgas.
As those sources are expensive and not usually available to non commercial customers, in support of federal guidelines listing it as a controlled substance used in the manufacture of illegal drugs, most folks use butane made for butane lighters.
Each manufacturers blend is slightly different, with n-Propane usually added as a propellant, because below the freezing temperature of water, butane is a liquid instead of a gas.
They also further refine the n-Butane to remove more of the low level oleaginous waxes, which clog the small orifices in expensive butane lighters. This is often shown on lighter butane cans as a number followed by an X. IE: 5X.
The common name for Oleaginous Waxes from petroleum, is Paraffin, which is non-toxic enough to have no known LD-50 data and be used to seal jelly jars, so they are of low concern when extracting.
Here Madison Avenue has gotten a foot hold, and even 7X butane is available for even more money, though there is no advantage over a good 4X for the purpose of extraction.
One refiner has started labeling the brand names that they produce, Near Zero Impurities, guaranteeing under 50ppm impurities. An independent test showed that they in fact are under 50 ppm, and even under the 15ppm testing cutoff, as were competitors brands not touting near zero impurities.
If using lighter butane, the safest course is to use tried and proven brands, but if forced to improvise, first obtain a MSDS sheet from that specific manufacturer, showing the contents. Reject any containing mercaps or Butadiene.
Ingredients less than 1% need not be shown on the MSDS sheet, unless they present a health risk at the levels present, so they are not all inclusive, but a good place to start.
If the MSDS looks OK, spray a five second burst on a mirror or clean glass pane and let it completely evaporate. Check for residue. Smell it for mercaps; you can’t miss them.
Each brand extracts slightly differently, because the mixes are slightly different. Adding propane for instance, increases water solubility and the propensity to pick up water solubles.
Here are some brands that we’ve tried and work well, as well as being tired and proven brands by others. This list is by no means inclusive:
Butane is highly flammable, so let us next talk about safety. First and foremost, always perform the extraction outside in a well ventilated area. Have a fire extinguisher handy, as well as a blanket to roll up in, should the unthinkable happen.
It goes without saying that smoking around a butane extraction is asking for a disaster, but I have literally grabbed the hand of folks starting to light up because they “forgot” where they were at and what they were doing. May I suggest that you leave your lighter and smokes somewhere else when you are doing extractions.
Same with your cell phone!
Wear no synthetic fabrics, including your socks, because static electricity sparks probably ignite more butane unintentionally than bone headed smokers.
We use a fan to disperse the butane rapidly so as to keep it from pooling. Butane is heavier than air and will collect in low spots given its own devices. We use a plastic fan so that no sparks are created by a piece of gravel or other hard material passing through the fan blades.
In dry cold conditions, we add a grounding strap to our cans, so as to not draw static electricity sparks between the can and the column.
Material prep will of course depend on the application, so lets cover that subject generally.
Fresh buds should be dry and cut into small pieces, before being stuffed into a column or thermos and placed in a -32C/0F freezer for 48 hours to solidify.
Buds for maximum terpene retention are best ground up after 5 to 7 days hanging, or as soon as the small stems break freely. They should be jarred immediately to retain freshness and run as soon as possible to prevent molding.
Buds for decarboxylation and most pristine appearance, should be placed on a coffee sheet and baked in a 94C/200F oven until just frangible, when rolled between the finger and thumb. They can then be ground or scrubbed through a pasta strainer to remove the sticks and stems. They should be jarred after grinding, to keep moisture pickup low.
The material shouldn’t be bone dry as it will become too frangible, nor should a coffee grinder be used, because of the fines that it produces, that have to be subsequently removed.
We also dry our trim and leaves until frangible as above and scrub ti through a pasta strainer, using a leather gloved hand and firm pressure, so as to minimize the amount of fine particles generated.
So now that we have covered some of the basics, lets move on to the different processes:
Simple Flow Through Column:
One of the simplest methods of extracting using butane, is a packed column. A column is a long narrow containment that allows a solvent to be passed though it using either gravity or pressure. The column is packed with plant material to be extracted and the essential oils are dissolved by the butane and carried out the filter in the bottom of the column, into a collection device.
Columns may be made from any number of different materials, but not all are suitable for butane service. http://www.coleparmer.com/Chemical-Resistance is an excellent site to check material compatibility with the various solvents. You do however have to read between the lines, and for medical use, stick with those materials listed as excellent.
Using those guidelines, a quick check reveals that Poly Vinyl Chloride (PVC), Acrylonitrile Butadiene Styrene (ABS), Low Density Poly Ethylene (LDPE), for instance, are not suitable, even though listed as good to fair, because the butane leaches out the constitutes, so they will end up in the meds.
They list copper as fair, not because the butane attacks it, but because of sulfur compounds and water that may be present in the butane, which form sulfuric acid and attacks the copper. Dry low sulfur butane doesn’t present the same issues, but copper columns have to be kept meticulously clean of oxides, as for instance, welding copper without adequate respiratory protection, produces a medical condition known as fume fever. If you do not have the time or inclination to keep the extraction column pristine, glass or stainless is a better choice.
Poly Propylene (PP), Poly Vinylidene Fluoride (PVDF), Polytetrafluorethylene (PTFE=Teflon), are listed as excellent, and High Density Poly Ethylene (HDPE), Ultra High Molecular Weight Poly Ethylene (UHMW), or Cross Linked Poly Ethylene (XLPE) may be, but are not listed.
Glass and borosilicate (Pyrex) work well, as does 300 series stainless steel. Neither are dirt cheap, but our local cost for borosilicate columns from the local scientific glass blower is only a buck an inch, plus five bucks to flare one end and close to an orifice on the other end. 1″ Stainless schedule 10 pipe was only $6.20 a foot, last time I checked, but prices vary considerably, so you should check local sources for pricing.
I don’t recommend single pass columns with a larger ID than 1″, as extraction efficiency drops rapidly above that size. Primarily because the material near the injection end is inadequately wetted, and because the larger the column, the easier it is for the butane to just find an easy route through, and continue to follow it.
The absolutely cheapest stainless column that I’ve found is one made from a stainless turkey baster from Bed,Bath, and Beyond for $7.99. Throw away the bulb and pull the press fitted needle out of the threaded adaptor, and you are good to go.
I’ve made a number out of copper, usually with a union near the injection end, so that it could be easily opened and cleaned. I also made a copper one with a can holder at the top, using a contractors size caulking gun, and my first experiments with pressurized butane extraction, were in a copper test sled.
In the latter case, we also added vibration and as we try to use free donated material where at all possible, I draw your attention to the gold plated personal vibrator used for that action and give thanks to the donor, whom wishes to remain anonymous.
A stainless column can be made by screwing a cap on one end and screw radiator clamping a double coffee filter over the other end. Drill a 1/8″ hole in the cap for the butane nozzle, and after thoroughly cleaning the insides by washing out with alcohol and boiling in hot soapy water, it is ready to go.
You can also stick a one hole Neoprene cork in the top of the column, instead of using a cap. It works well enough, though more sensitive to blowouts.
We have our borosilicate columns made and some development was required to stop breaking them in cold wet weather. What was required to stop spalling off conchoidal divots from the injection port in frigid weather, was to make the closed end a smooth even radius of uniform thickness, so that stresses from uneven expansion and contraction were not an issue. You also need to insure that the column is annealed after forming, to relieve all residual stresses.
We add a flare to the ends of our borosilicate columns, to make filter retention easier, so as to reduce blowouts.
A blowout, is where the filter at the end of the column ruptures and blows the column contents into your collection vessel, or the filter blows off entirely, doing the same thing, or when using a cork in the top, it blows out during injection.
You can guard against filter rupture, by backing the coffee filter with stainless mesh, or cloth.
Preventing a blow off gets trickier with glass tubes, in that you can’t just crank down harder on the radiator clamp, without breaking the glass. Alternatives that work better with glass, are twine wraps, zip locks, or rubber bands. We mostly use rubber bands, and stretch them tight.
When loading the material in the tube, we use a wooden dowel to keep it uniformly and firmly, but not tightly packed. A dowel close to the ID of your column will make even packing easier.
Before loading the tube, we wad up a coffee filter and stuff it in the injection port end, to diffuse the butane as it enters and so that no plant material blow back out into our extraction, should for any reason we need to release butane pressure in the middle of the process.
We cut the top out of a water bottle to use as a funnel, and pack the material as we load it, stopping about every foot to compact. When the column is full of plant material, we double a coffee filter over the end, and then cover that with a cloth patch, securing both with multiple tight wraps of a heavy weight rubber band.
We also scissor trim away all extra filter material, so as to minimize the oil soaked up during the process. I find that if I am careful removing the filter after an extraction, that I can reuse it multiple times, so as to further minimize losses. We also wash out our filters in alcohol, to recover any essential oils soaked into them.
Skunk pharm use of a column is common general practice, though our collection and processing techniques deviate from the norm. We simply support the column full of pulverized plant material over a collection vessel and inject butane through the top port in the column, and let gravity carry it through the column.
As the butane passes through the material in the column, it dissolves the trichomes, and conveys them out the end of the column, into the collection vessel. The butane subsequently evaporates off, it leaves the extracted cannabis oil behind.
When the stream of solvent running out of the bottom runs clear, we cease injecting butane and insert a basket ball pump needle into the injection hole and blow out any remaining liquid. A modified butane can nozzle adapter will adapt the needle to seal the hole.
Examination with a microscope will tell you when the trichomes have been dissolved away, and looks like wet hairs lying down, with the capitate heads missing. Our average yield at this point was around 17 to 18% by weight, but we’ve yielded up to 21.6% by dumping the column, repacking it, and making a second run.
This second run will be less heady, and of lower viscosity, with more sedative properties, so we keep it separate from the first.
How we are going to use the oil, to a large degree dictates how we collect it, so lets look at some of the methods we’ve found effective.
Pyrex Pie Plate:
The first that I tried, was collecting in a 10″ Pyrex pie plate, sitting in a larger Pyrex dish full of hot tap water. That works well and the key is the hot water that it sits in, in at least this neck of the Pacific NW rain forest, where we often have high humidity. If we don’t set it in hot water, ice forms at the edge of the evaporation pool, adding considerable water to the mixture.
The hot water also rapidly boils off the butane, until all of it visibly gone, although some remains un-purged and in solution with the oil. Techniques for purging the remaining material vary, so we will cover those steps as a separate issue.
This technique is suitable for any process, with certain precautions and subsequent processing.
Stainless Bain Marie:
Even better in this land of the midnight rain, is a deep stainless bain marie container, sitting in a hot water bath. The deep vessel fills with butane fumes, which floats away the atmosphere, so that no moisture laden atmosphere is anywhere near the evaporation line of the butane. That is how we processed most of our oil, when using single pass columns.
The real advantages to using this type of collection, are that it can be wiped dry on the outside and the pot set directly into a hot oil pot for a rapid purge and decarboxylation, followed by formulation in the same stainless vessel, so that nothing is lost to films left behind in transfer pots. We have the tare marked on each of them, so that we can weigh the material while still in that pot, to establish yield, and the quantities for the rest of the ingredients.
This system works well for decarboxylated and formulated meds, but presents a challenge to remove the oil afterwards, if you are not, and has less surface area for evaporation if you aren’t planning to hot purge or wash it out with alcohol and do thin film vacuum purging. Absolutely the best method we’ve found overall, subject to the above limitations.
Butane is relatively easy to purge from cannabis oleoresins or concretes, as it has a boiling point of around -.5C/31.5F, or right about the freezing point of water. Given enough time just sitting around, it will purge below our 5000 ppm smell sensory threshold, and even our far more acute sense of taste, either of which is a small percentage of the 658, 000 ppm, that the MSDS LD-50 tells us it took to asphyxiate 50% of the test rats in 4 hours.
We can speed up that purge, by using a dish with a large surface area, relative to the depth of the pool of oil. Usually small extractions, so as to keep the pool depth thin, are the easiest to purge.
Typically, the thin film is scrapped and stirred periodically, to speed up the process, and a flame may periodically be lightly run over the surface, to warm it and determine if the bubbles exiting are butane and terpenes, or CO2. Some care needed here, as THC, CBD, and CBN are di-terpene alcohols, and are flammable themselves, as are the other terpenes present.
Air movement over the pool speeds up evaporation, by whisking away the saturated boundary layer and providing the extra energy for the molecules of butane to escape the surface of the oil, as it is ricocheting about in the pool. Care must be exercised here, as any dust or lint in the air will end up in the oil, so usually a cheese cloth or similar porous cover is placed over it, before blowing over the top with a fan.
We can also speed it up with the application of heat. Any heat will speed up the evaporation, and one line of thought is to keep the heat low and around 60C/140F, using a hot pad after the hot water bath and scraping and popping any bubbles with a razor blade. A typical purge might take an hour and provides maximum terpene retention.
When adding bottom heat, you can also add a loose fitting lid, which will speed up the purging and keep out lint and dust.
For a faster purge, the temperature can be raised to above the melting point of the cannabis essential oils, or around 82C/180F, to give the butane molecules maximum mobility.
Instead of heat, vacuum may be applied to speed up the purge process. That is the process that we use when we wish to maintain the cannabinoids in their carboxylic acid forms.
In thin film vacuum purging, we place about an 3/16″ of the oil in a 6″ Pyrex Petri dish, and place that in a vacuum chamber, which also contains a hot plate. That allows us to manipulate both the temperature and atmospheric pressure, so that we can achieve boiling at very low, or even ambient temperatures.
While we use 180F to vacuum purge a raw oleoresin, adding heat isn’t necessary when thin film vacuum purging raw oleoresins redissolved in ethanol. The alcohol will boil away under 28.5″Hg at ambient temperatures, as will the water that is left behind, even without adding any heat.
For our oral and topical meds, we exclusively used the bain marie collection vessel, and simply wiped the water off the outside, following the hot water purge, and set it in an electric fondue pot full of hot 121C/250F Canola oil.
The residual butane will boil off first, exiting in larger, multi sized bubbles, followed by the smaller equally sized CO2 bubbles from decarboxylation.
Depending on the use, we remove it from the hot oil when the bubble activity suddenly slacks dramatically off, indicating the 70% peak of the decarboxylation curve, or when it becomes quiescent, if we are looking for maximum sedative effect.
Hot oil Pots:
We use electric fondue pots for decarboxylation and I prefer the Quisinart, for their sensitive controls and narrow dead band. We also have a couple of Rivals, which work well too, but whose controls aren’t as sensitive.
Some fry cookers may have sensitive enough controls, but most are designed to primarily run at 375F, and lack control sensitivity, as well as have a large dead band at 250F.
It is important to make sure that the container is sitting on something that suspends it up off the bottom of the oil pot, to eliminate direct transfer hotspots. We keep several jar lid rings in the bottom of our electric fondue pots for that purpose.
We never trust any controls however, and use a good mercury lab thermometer, a digital, or an infra red optical pyrometer to establish and control temperatures.
Thermos extraction is a technique allowing an extended soak period at atmospheric pressure. At sea level, n-Butane boils at approximately -0.5C/31.5F, so unless the local ambient temperature happens to be under that temperature, the butane will warm up enough to return to its gaseous state.
In thermos extraction, the prepared material is loaded into a stainless steel thermos bottle and frozen before having pre-chilled butane added. The thermos acts as a Dewar to keep the butane temperature low enough to keep it in its liquid state.
Dropping the temperature will of course also slow down the extraction rate, so the resident soak time must be increased to compensate.
An advantage of keeping the temperatures low, is that it allows you to run fresher material, as the water will be tied up in the form of ice.
Butane has the very slight water solubility of 0.0325 vol/vol, or about 32 milliliters per liter. That means if there is any water available, some of it will come along and bring with it undesirable water solubles, such as chlorophyll.
Tying the water up as ice, allows a longer soak resident time, without picking up those water solubles. Operating at 50F outside temperatures locally, an optical pyrometer showed the butane in the thermos to hover around +8.7F, with mild bubbling action and minimal loss of liquid.
Because of the low operating temperature, you can run either fresh frozen or dried material equally well and can therefore control a wide range of flavors, by simply controlling the pre extraction state of drying, and evaporation of aromatic terpenes.
A fully cured material will produce hashy tasting oil, and fresh material will produce floral oils, and the rest of the flavors will be in between. The flavors besides cannabinoids, are the lighter mono and sesquiterpenes, which are the aromatic alcohols, phenols, ketones, aldehides, and esters.
Equipment required for this process are minimal. I scored a gorgeous little stainless steel thermos at the local Goodwill for $4.99 and my only alteration was to drill three holes in the cap. One to fit a lighter butane can nozzle, and a couple to allow venting during injection. I tossed the inner lid, as the gasket was unsuitable for butane.
After soaking one hour, we pour the butane through a strainer suspended over a bain marie catch vessel, but we also subsequently winterize, so if you aren’t going to, you can rubber band a coffee filter over the opening and dump through that.
A second soak in chilled butane may be used to extract any remaining essential oils. Jump, one of the developers of the process, reports using a 30 minute first soak, and a 2 hour second soak, with pictures showing pristine quality from both extractions.
Once in the catch vessel, the extract can be purged any number of different ways, like any other BHO extraction.
Notice in this case, we broke up the buds and removed the stems in a harvest box, which we subsequently harvested the kif out of for our pipe while standing around.