BHO is the acronym for Butane Honey Oil, which is cannabis essential oils extracted using LPG as a solvent.  That LPG typically contains n or iso Butane and may contain some Propane. 

Some processes use 100% propane, but those are more properly called PHO.

Butane and Propane are both listed as a GRAS Class III solvent by the FDA for use in food and pharmaceutical products.

LPG is a non-polar solvent, so isn’t prone to pickup polar elements like water, water solubles, or chlorophyll, but does extract nonpolar plant waxes, as well as deprotonated chlorophyll in the form of Pheophytin.

Essential oils extracted from fresh material is referred to as a Concrete, and an Oleoresin when extracted from cured material.  An Absolute is a concrete or oleoresin that has been winterized to remove the waxes, fats, and lipids.

Removing the plant waxes also removes an extracts cloudy haze and gives it bell clear jewel like qualities.

Absolute winterized Oleoresin

We have yielded as high as about 18% and as low as 5.7% absolute, depending on strain, but crude extraction contains non target elements, so yield will be higher depending on process.

Processes that extract with the LPG at subzero temperatures extract less non targeted constituents, so do not lose as much at winterization, or those elements are low enough to not require subsequent winterization.

Our BHO extraction experience has evolved from open blasting with simple columns or a thermos, to using a pressurized and vibrated column, and then to using both passive and active closed loop systems.

This article is about how to open blast with a column, and the other processes will be covered in a separate article. 

I actually deleted all of my previous open blasting blogs, because there were so many buildings being blown up, as the ill fortuned extractors were ignoring all caveats and violating the first cardinal rule of open blasting, which is to do it outside with adequate ventilation.

I’m posting this tongue in cheek, and only because closed loop system explosions have taken over the news of late, due to indoor extraction without proper NEMA 7, C1D1 electrical or adequate ventilation, but more importantly, medical cannabis patients around the world may not be able to obtain their medications from others and may not have the resources to assemble and operate a closed loop system.

If professionally extracted cannabis concentrates are available to you, or you do have the resources to assemble a closed loop system, I highly encourage you to do so, for not only safety reasons, but because of Mystery Oil issues when using LPG from lighter cans and environmental impact.

Consider the impact on Ma Earth from crude oil exploration, extraction, and refining, even before you release it directly into the atmosphere to become smog components.

Also consider other less impactful processes like QWET.

Having said that, if your options are limited to open blasting, lets discuss how to do it sanely. 

LPG is flammable and explosive between its Lower Explosive Limits (LEL) of about 1.8% (C-4) to about its Upper Explosive Limits 9.5% (C-3). 

Please read for those details before proceeding further and note the explosive limits of various solvents in the following chart:

Upper and Lower Explosive limits of various solvents

From an equipment standpoint, extraction columns are available online, or you can build your own, and they needn’t be fancy.  I’ve built them from copper and stainless, as well as had them custom made in borosilicate by a local scientific glass shop.  You can also repurpose existing devices like stainless turkey basters or barrel theives.

$7.99 Turkey baster column from Bed, Bath, and Beyond

18” Barrel Thief used in wine industry

DO NOT USE PVC PIPE, as LPG leaches the plasticizers out of the Poly Vinyl Chloride and deposits them in the extract.

If you use copper, use lead free 95/5% solder and keep the copper surface clean and free of oxides.  I also added a ground strap to mine, so that the column and can were at the same electrical charge and potential before injecting. 

For open blasting, I’ve found one inch diameter to be about optimal for efficiency, and 36” to be about the maximum efficient length.  Larger diameters get less even wetting, especially at the injection end, and longer can over wash one end of the column, while under washing the other.

One end of the column needs to be closed, except for a 1/8” injection hole for the nozzle of the lighter butane to be inserted, and the other open.  After the column is packed, the open end is covered with a filter and support screen, which is retained with bands or clamps.  Often the discharge end has a bell or feature aiding in retention of the filter and screen.

Unless you want to hold both the column and the can throughout the extraction, you will need something to support the column, and of course you need a container to discharge into.

I like to repurpose things, so made simple wooden clamps to support the columns in conjunction with a modified cat liter plastic bucket.  The bucket was modified to straddle either a 10” Pyrex pie plate, or a stainless bain marie container from the local restaurant supply sitting in hot water.

The following picture is my first column sitting in its modified cat litter bucket stand, straddling a 10” Pyrex dish.  Note the ground clamp as well as simple tape retaining the end caps instead of solder.

Insulated copper column with support clamp, ground lead, modified bucket, and bain marie ware

Improvised can clamp

Borosilicate Columns.  Note flares on discharge ends to aid in retaining filter and screen

Note the borosilicate columns in 12”, 24”, and 36”, as well as the improvised clamp and pipe insulation.

Injection port

System ready for injection

You can also build a column using a stainless steel sanitary spool with a tri-clamp endcap.  Besides being sturdier than glass and easier to keep clean than copper.  You could also plumb a tank to it using a hose, so as to use commercial LPG vis a vis lighter fuel.

Stainless Sanitary Spool

FNPT Endcap

Before moving to closed loop systems, we also experimented with closed and pressurized systems, to increase the solvent resident time and provide agitation in the form of vibration. 

We built a horizontal column with removable elbows at each end.  The elbows had valves and unequal length risers, so that when we injected liquid in the tall one and liquid spurted out the short one, we knew it was free of trapped air.

We then closed both valves and turned on the vibrator donated to the experiment by an associate who found something that worked better for other experiments that they were conducting.

While the system extracted more material, it was primarily non target elements, so we moved on to closed loop designs.  That was before we became aware of the effects of subzero extraction, which would have changed the dynamics some and been more successful.

Prototype pressurized and vibrated test sled

Besides the column and ancillaries, you will need butane that has minimal undesirable contaminants, and all brands are not all created equal.  Consider that they need to be clean enough to not plug the lighters fine orifice with oleaginous waxes, and to operate at ambient temperature extremes.

We call those oleaginous waxes Mystery Oil and while there are measures that can be taken with a closed loop system to remove them, when open blasting from lighter cans, what you see is what you got.  That suggest discrimination in picking the brand of lighter LPG chosen to minimize the risk.

Check out my post at Mystery oil content by lighter fuel brand by Skyhighler or his original post at:

While lighter butane is primarily n and isobutane, they also contain propane to supply operating pressure at low temperatures.  That formulation can change depending on location and the temperature extremes they were formulated for. 

More predictable is 99.95% Instrument Grade or better supplied in reusable DOT rated tanks, which we get from places like Apis Labs in Eugene, OR.  They can be used in conjunction with a stainless sanitary spool with an injection orifice in the tri-clamp endcap, connected by a hose.

Once you have your equipment, the next step is to load a column, which brings up the question of what end product do you covet ending up with?

Oral and topical meds are treated differently from those intended for vaporization.  Primo buds are also typically treated differently than low grade trim, or fan leaves and stems.

We don’t manicure our own grows, just remove the fan leaves and hang the plants upside down for 5 days to a week until the small stems snap. To prepare those for extraction, we typically break the flowers into about ½” chunks either by hand, or using a bud buster such as the following:

Bud Buster

At the Pharm, we often had patients donate low grade trim, which we extracted and provided the concentrates to other patients pro bono.  We typically processed that trim by loading it on cookie sheets and placing them in a 200F oven until just frangible when rolled between the index finger and thumb, before scrubbing them through a 10 mesh pasta strainer.

Oven drying low grade material

Passing material through a 10 mesh pasta strainer

The next step is to pack the column.  I always pack the injection end of my column with a coffee filter, to catch blow back and diffuse the incoming LPG stream.  I use a wooden dowel the size slightly smaller than the column to pack it.

I load the column and pack it evenly, firmly leaning on the dowel until it stops, but not using percussion to pack it further.  I get about 3.8 grams per cubic inch of column packing ½” chunks, and about 4.1 grams per cubic inch packing 10 mesh that has been oven dried.

I pack my columns within about an inch of the discharge end, and then wad up and pack coffee filters on top to protect my discharge filter cover from blinding. 

Lastly I cover the end of the column with a doubled coffee filter, which I cover with a piece of silkscreen or wire mesh as a blowout preventative, and hold the whole thing in place using a screw type radiator clamp. 

It will be more secure if the discharge end of the column has a slight flare and blowing a column into your collection vessel is messy, so close attention is required here.  As you inject the LPG, if the end filter begins to blind and pressure builds up in the column, I can either blow a hole through a paper filter, or blow the whole filter assembly off the end of the column.

At this point I recommend that you place your packed column into a -18C/0F freezer overnight, and place your cans of butane in a cooler full of ice overnight, sitting somewhere so that if a leak occurs, there is adequate ventilation and no ignition sources.  Chilling elastomer seals hardens them and they can be less forgiving.

These freezing steps are not absolutely necessary and are intended to limit pickup of longer chain non targeted elements like plant waxes.

We found that it takes about one can of lighter LPG per foot of 1” column, but the way to tell how much oleoresins are still coming through is by both looking at the color of the discharge and feeling it between a finger and thumb for stickiness.

We originally discharged our columns into a 10” Pyrex pie plate and then set it in hot water to purge, but subsequently switched to a stainless bain marie sitting in hot water and that is what I recommend.

10” Pyrex pie plate purging in deep dish full of hot water

Not only is it less messy, it is more efficient for most applications.  As you can see from the following picture, the column is supported by a wooden clamp sitting on a modified plastic bucket, and discharges into a stainless bain marie container sitting in another stainless bain marie full of hot water.

Bain Marie components

Assembled and ready to inject

The next step is injecting the lighter LPG into the column.  Install the proper size taper tip on the lighter fuel can, and place it into the injection hole in the top of the column and press down hard enough to seal the taper against the injection port and discharge the can,

You can hear the can discharging until it reaches the end and then the best way I’ve found to tell is to wiggle the can so as to slosh any remaining liquid about, which will chill the can.  Careful removing the can if injection is interrupted or you are changing cans, because any pressure build up in the column can blow backwards and contaminate your extract with small plant particles.

Injecting.  Note outdoors and fan blowing, not sucking fumes away from area.

After the last can is empty, we blow the remainder of the liquid out of the column with a bicycle pump.  Some simply blow with their mouth.

Blowing out remainder with pump

When open blasting, we try to extract about 80% with the first pass, and gleaning the rest after emptying and repacking the column.  The second extract will have more of the heavier molecules and will be more sedative than heady.

How we treat the extracted oil after blasting, depends on our intended purpose.  For instance if we don’t intend to winterize it after extraction, the evaporating mixture can be poured into parchment paper trays once it is mostly evaporated, but before it turns to thick syrup. 

The parchment trays are then placed in a vacuum chamber or oven for final purging into shatter.

If it is going to be winterized, as soon as all visible LPG has evaporated, we add 190 proof Ethanol directly into the bain marie to dissolve the oleoresin and then pour that into a canning jar before sealing and storing in a -18C/0F freezer for about 48 hours.

If it is to be decarboxylated for oral use, the bain marie can be set directly in a 250F oil bath, so as to purge and decarboxylate in one step.

A form of concentrated marijuana called ‘shatter.’ When dried, this substance is brittle and easily shatters into tiny shards or flakes. After being heated the concentrate is spread out on parchment paper to cool. This shatter has cooled, which contracts the liquid, creating the holes in the poured material.


Winterized precipitated waxes ready for filtration

Winterized shatter

Decarboxylating.  Note fine fizzy CO2 bubbles.

Fully decarboxylated extract.  Note quiescence.

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