What causes the burnt taste when the atty runs dry?

[SilentJay]

I've been wondering this for awhile. If I'm dripping the taste is great at first but begins to get "burnt" as the liquid is consumed. Same thing with a tank that gets clogged. I've been vaping 100% UNFLAVORED VG, so it's not the flavorings building up on the atty. I've gotten the same taste with silica and cotton wicks (happens long before the wick is dry enough to burn).

Seems like it must be the VG oxidizing in the heat. Acrolein? Or some other by-product of over-heated VG? Or could the nicotine get affected as well?

 

[hazarada]

mostly acrolein, even though the actual amount of it is very little, its very offensive to human senses

 

[SilentJay]

mostly acrolein, even though the actual amount of it is very little, its very offensive to human senses

Hmm, despite what the rolygate article says, I wonder if it's harmful to experience that periodically (usually due to hitting the dripper one too many times, or on the first hit if unable to get the wick working in a tank setup). He also makes the argument that anything else dissolved in glycerine will drop the boiling point, which may offer some protection. However, I prefer 100% VG (no water, no flavor, no nothin but nic added). Maybe I should dilute it a bit just to move the boiling point away from the decomposition temp. Sad, water mutes the taste and throat hit.

 

[Kurt]

Unthinned VG boils at 290C, so pretty high. The coil is pretty hot when it goes dry, and thermal decomposition is easier. Even just 5% water will lower this a lot. And a little water added actually increases the TH to me, and opens flavors up more. With unflavored VG-nic, I use 20% distilled water. Increases wicking better too, which helps to feed the coil and keep it wet.

And yes, it is likely that acrolein is formed in the thermal decomp of VG, but it is a very small amount, as far as we know, and the nose is VERY sensitive to it, since it is a strong lacrymator (tear/burn maker). Other compounds can form too. Thermal decomp and burnt taste/smell should be avoided.

You may get less TH with a water-thinned VG-nic, but it vaporizes with less heat and is much less likely to decompose.