So you’re ready to learn how to vacuum purge BHO, aka butane hash oil. If you haven’t already extracted any BHO, you can check out our tutorial: How to Make BHO.
It is very important to properly vacuum purge your BHO. Vacuum purging improves its texture, consistency, taste, and purity by removing your solvent and contaminants.
The easiest way to remove a solvent from your oil is to boil it. However, when boiling BHO, it can get too hot and cause decarboxylation and darkening of the oil. To get around this problem we need vacuum purge BHO in order to allow the solvent to boil off at a different temperature.
The Science of Vacuum Purging
Back in high school, you may have learned how a vacuum affects a boiling point’s temperature. As the atmospheric pressure in a system is lowered, the stuff in the vacuum becomes more volatile and will boil at a much lower temperature. For us, this means we can vacuum purge to boil off the butane and not damage the quality of the BHO.
The graph below shows the boiling points of various solvents at different atmospheric conditions. Since you generally use butane for BHO, we should pay special attention to the green line. If you happen to use IsoButane, check out the orange line.
Measuring The Pressure
When purging BHO, most people and vacuums will measure the atmospheric pressure in “inches of mercury”. Most commonly denoted as inHB or “HB, the term “inches of mercury” has its roots in old school barometers. At 1 atmosphere, the mercury in a barometer will move up to 29.92 inches in the tube. This is the pressure you and I are experiencing this very moment, varying slightly based on altitude, relative to sea level.
Our goal when purging BHO is to achieve a system as close to -29.92 inHG as possible. When -29.92inHG is met, an absolute vacuum is created, devoid of all atmosphere. It is tough to get a true vacuum, really tough, but that is the goal we are heading for so how close can we get? Fairly close it turns out, depending on how extreme you want to get.
Choosing The Right Purging Equipment
How do we get it done? There are several levels of quality of equipment, and in general, you get what you pay for. Any vacuum purging will help, but for lab grade quality you need lab grade equipment.
On the entry level, or personal production side of things there are people using vacuum sealers designed for food preservation such as the FoodSaver 3460 seen here. In this video, it is demonstrated the lowest pressure that a food saver can achieve is -20 inHg. This will absolutely help the quality of your BHO and is easily accessible, but we can do better. If you already have one of these around, picking up a jar may be a good cheap start down the purging path.
Another entry level method is a hand pump made for bleeding brake lines, seen here demonstrated by a gentleman rebelling against shirts. In this video, he states that the lowest pressure achieved was -27 inHg. This is a pretty good vacuum, especially considering it is coming from a hand pump. It will work fine for small chambers, and batches. In practical terms, however, it would take forever to pump out the air in a larger vacuum chamber for larger batches. If you are making small batches for personal use, this is a fine option, and should be readily accessible.
The next step up is a purpose made vacuum chamber and an electric pump. If you are the handy type and see value in creating things from scratch, here is a great video on making a vacuum chamber. Be forewarned you will need some machining experience, and general handiness to pull this off and get a perfect seal. If you have the skills, this is a great option for customizability and scalability.
If you are more of the pick up a thing that someone who knew what they were doing built type (like me), You will want to head toward pre-made vacuum chambers. There are some companies that sell them with Pyrex glass chambers, but I don’t like that idea as a little crack turns into a big problem under vacuum. I recommend staying with a metal chamber, just get the size that makes sense for your batch size. Remember to leave some room for expansion as your solvent boils off as the BHO tends to bubble and rise up, forming a ‘cookie’. If I was making larger batches, this is the kit I would go with today.
Once you have a vacuum chamber you will need something to run it, specifically a 2 stage electric vacuum pump. You can have terrific results with a regular two stage vacuum pump, and keep getting better the more you are willing to invest. Ideally, you will be moving towards an oilless vacuum pump, avoiding the oil break down from solvent being pulled through the pump, and any chance of oil being pulled back into your dab. Just read up on descriptions and ensure that it is strong enough to pull the desired vacuum.
One example of a ready made vacuum chamber and pump combo can be seen here degassing silicone. This is very similar to the process we are trying to achieve.
It is crucial you only use high-quality silicone in a vacuum chamber. Cheap silicone has plasticizers in it, and the will leech into your oil and make it take like rubbery hell. One way to tell if the silicone has plasticizers in it is to pinch and twist the silicone. If it turns white and cloudy as you twist it is no good to use in a vacuum. Silicone Alley makes a very nice kit that has mats, storage containers, tools, and a sweet holder to make dabbing super easy. Rest assured that these mats are good to go inside of a purging chamber, these are the exact ones I use. If you are doing larger runs, they also make some larger silicone mats as well that will fit inside of your purging chamber nicely.
BHO Purging Safety
You are working with solvents that may be explosive. There is a real danger here, and a few precautions are needed to limit your exposure to fireballs. Throughout the process, you need to be aware of ventilation, to avoid butane build up in your room. In addition to that, you need to also be cognizant of flame, sparks, and heat. Any of these things can set off a fireball that fills the room faster than you can think or react. This WILL result in severe injury, loss of life and property
How To Vacuum Purge BHO
Now that you have extracted you BHO and you have the right equipment, it’s time to get to the vacuum purging.
Take your solution of butane and THC goodness and put it in a Pyrex dish. Then place it in a bath of hot water that’s no hotter 140 degrees. It should be about the temperature of a hot tea or coffee. One you have safely boiled off the majority of your butane, you will be left with the BHO in the pan, as it reaches a syrupy consistency, and can be scraped up, use a single edge razor blade to scrape it up, and place your dab on a silicone mat. Try to keep your pile on the thinner side for best results.
Take your silicone pad and place it inside of your vacuum chamber of choice. If you are using one of the smaller containers, and a dab mat will not fit inside of your chamber, Parchment paper can also be used. Once your dab is in the chamber, seal it up, and start pumping. You will want to run the pump until your gauge stops moving, somewhere between -27 and -29.92 inHg, the stronger vacuum you can pull the better. Once it reaches that point, place your chamber somewhere warm preferably on a digital heating pad. I like to set the heating pad to 110 degrees at this point, as I try to not be in a hurry and rush things that can lead to poor quality in otherwise great oil. You now have a sealed container heated to 110 degrees that contains oil on a silicone mat inside.
This container is under a vacuum and you should see your oil boiling as the butane, and any water in your dab boils off leaving nothing but pure wonderful behind. After a few minutes I like to let the atmosphere back in and then pull another vacuum, this allows any solvent that is in the system to get pulled out rather than forming a vapor layer in the chamber. Repeat this until your dab bubbles slowly, then pull a full vac, put it on the heating pad and leave it for at least 24 hours. If you are bored, letting off the vacuum and then re-vacuuming will not hurt a thing, just let air in slowly each time you reintroduce atmosphere. After 24 hours I like to take it off of the heat, pull the pad out, stick it all together in one pile, and revac, squish into one pile, roll it out super thin and then re vac for a few more hours. I then remove my dab, place in a freezer for a minute or two just to firm up, and It is good to go.
Thanks for reading our post on how to vacuum purge BHO. Please let us know how your BHO turned out in the comments below.