Answer
A cannabis vape tastes burnt at high heat because the coil runs hotter than the oil can take. Terpenes break down above about 400°F. Cotton wicks char near 420°F. Glycerol and propylene glycol, the thinners in many carts, form acrid compounds above 450°F. The burnt note is degraded oil, not the strain.
Vaporization points of cannabis compounds
Each compound in cannabis oil boils at a set temperature.
- THC: 315°F (157°C)
- CBD: 356°F (180°C)
- CBN: 365°F (185°C)
- Pinene: 311°F (155°C)
- Myrcene: 334°F (168°C)
- Limonene: 349°F (176°C)
- Linalool: 388°F (198°C)
Most 510-thread carts and pod systems fire between 350°F and 450°F. A setting at the top of that range pushes past the point where terpenes survive.
Cannabis Concentrate Vape Temperature Chart: Best Temps for Dabs
What happens above 430°F
- Terpenes oxidize. Aroma drops, and the vapor picks up a bitter, ashy note.
- THC degrades into CBN. The hit gets heavy and sleepy, with less head effect.
- Glycerol breaks into acrolein. Acrolein is a lung irritant with a sharp, burnt smell.
- Propylene glycol forms formaldehyde and acetaldehyde at coil temperatures above 450°F.
- Cotton wicks char. Charred cotton tastes like ash and does not wash out.
- Plant waxes and lipids in less refined oil scorch before the cannabinoids boil.
Hardware causes
Wattage comes from voltage and resistance. A 1.5-ohm cart at 3.7 volts draws 9.1 watts. The same cart at 4.8 volts draws 15.4 watts. That extra 6 watts raises coil temperature by hundreds of degrees in a dry spot.
Three hardware faults lead to burnt hits:
- Voltage set too high for the cart resistance.
- A clogged airway. Pulling against a clog pulls oil away from the wick, and the coil fires dry.
- Low oil. Once the level drops below the intake holes, the wick runs dry and the coil spikes.
Oil causes
Cut agents lower the boiling point of the mix. Polyethylene glycol and propylene glycol thin thick distillate, and both break down at heat. Botanical terpenes added back after distillation burn off sooner than cannabis-derived terpenes. Oil that was winterized poorly still holds fats and waxes, which scorch at coil temperature.
How to fix a burnt-tasting cart
- Drop voltage to 2.5 to 3.3 volts. Most live resin and distillate carts work in that band.
- Take 2 to 3 second draws with 30 seconds between them. Long draws heat the coil faster than oil can wick back.
- Store the cart upright. Oil feeds the wick by gravity.
- Prime a new cart with 2 dry pulls before firing the battery.
- Stop when the oil level reaches the top of the intake hole.
When heat is not the cause
A burnt taste at 2.5 volts points to something other than temperature. Causes include a wick that was dry-fired at the factory, a cart near empty, or oil made from old oxidized material. In those cases a lower setting will not help. Replace the cart.