I've been extracting flavor from tobacco and making NETs for years. NETs are notoriously hard on wicks and coils, they're "gunky". To be fair any natural extract that's used to flavor e-liquid (juice) will be gunky for the same reason NETs are. Regardless of what solvent and method of extraction is used, along with the desired "flavor" plenty of wax, oil, resin, sugars, chlorophyll and other undesirable constituents of the tobacco are inadvertently leeched into the extract. To be terse, I simply refer to these undesirable elements as "muck".
When you vape NET the muck it contains doesn't completely vaporize. The PG, VG and most of the flavor molicules do but the majority of muck gets left behind, gathering in the wicking material. It saturates the wick and begins caramelizing on hot coils forming the thick, crusty, burnt coating (and taste) you're familiar with. Depending on a person's level of tolerance this can lead to re-wicking and dry-burning coils after just a single tankful (~3ml). The type of tobacco, how it was cured, casings, top notes and even the method/solvent used to extract it directly impact how gunky a NET will be. Many people have accepted the gunky nature of NET as being unavoidable and to an extent, they're right. NETs will never enjoy the same level of performance as a clear, unsweetened, synthetic flavored juice. Some people even go so far as inferring this muck is necessary in order for NETs to have a full tobacco flavor but in fact this isn't true. The muck is actually a flavor inhibiting, coil/wick trashing contaminant that contributes -nothing- beneficial. It's an unavoidable byproduct of the extraction process.
Mechanical filtration removes any particles of tobacco and other debris from the extract helping to improve its performance. Unfortunately, mechanical filtration is of limited effectiveness in removing the extracted muck. This is because mechanical filtration is good at catching particulates (small particles suspended in the solution) but not good at removing compounds that are dissolved in the solution (solutes). In extracts the solutes (dissolved muck) and extraction solvent form a "homogeneous mixture" that will pass straight through even high retention absolute filters (<1 micron). The only way I've found to remove the muck (without also removing flavor) is by first changing it's state from a solute to a "precipitate" (a separated semi-solid), only then will mechanical filtering be effective at removing it.
When using 190 proof Pure Grain Alcohol (ethanol) as the extraction solvent, a good portion of the muck can be removed through a "freeze filtering" process. This is accomplished by placing the sealed container of extract in a freezer for 72 hours, the colder the temperature, the more effective the process will be. Exposure to extreme cold causes a "precipitation" reaction to occur and over time a substancial portion of the muck will fall out of solution, changing from a solute (dissolved muck) into a "precipitate" (seperated semi-solid muck). As it falls out of solution the precipitate coalesces in the bottom of the container. After 72 hours (and while still in the freezer) the extract is filtered. Here's how much precipitate (muck) was removed from ~50ml of an ethanol based tobacco extract;
For larger batches of ethanol based extract, there's a more effective technique of purification available. It involves freeze filtering "reduced" extract. To reduce an ethanol based extract you simply evaporate a large portion of the ethanol off, the portion that remains is highly condensed. Once reduced the remaining condensed extract becomes oversaturated with solutes making the freeze filtering process even more productive. To illustrate how effective the purification process can be here's what coils and wick look like after vaping (dripping) ~10ml of NET made from highly purified extract;
The most common extraction solvent used by DIY home extractors and retail NET vendors is Propylene Glycol (PG). Neither PG nor VG based extracts can be freeze filtered, however, out of necessity, I did find a way around this. I Mixed a well aged, highly filtered PG/VG based extract with an equal amount of 190 proof PGA (ethanol). I allowed this mixture to sit at room temperature for a day and then placed it in a freezer at -20F. After 72 hours (and while still in the freezer) the extract was filtered. Here's a pic of the muck removed from just 55ml of PG/VG based tobacco extract;
The 80/20 PG/VG extract had already been vacuum filtered through an absolute 1 micron borosilicate glass lab filter so what you see is what mechanical filtration alone couldn't catch without first adding ethanol and then freeze filtering the mixture. You're looking at "the muck" that makes NET so hard on wicks/coils. I don't suggest purifying PG/VG based extracts this way, there's no point since you could just use ethanol for the extraction solvent to start with. I developed this method because I have a lot of well aged PG/VG based extracts made from tobacco that is no longer sold/available. Since these extracts are irreplaceable I wanted to find a way to purify them. After freeze filtering was complete I simply evaporated the added ethanol off and re-filtered the extract through a 1 micron paper lab filter.
When you vape NET the muck it contains doesn't completely vaporize. The PG, VG and most of the flavor molicules do but the majority of muck gets left behind, gathering in the wicking material. It saturates the wick and begins caramelizing on hot coils forming the thick, crusty, burnt coating (and taste) you're familiar with. Depending on a person's level of tolerance this can lead to re-wicking and dry-burning coils after just a single tankful (~3ml). The type of tobacco, how it was cured, casings, top notes and even the method/solvent used to extract it directly impact how gunky a NET will be. Many people have accepted the gunky nature of NET as being unavoidable and to an extent, they're right. NETs will never enjoy the same level of performance as a clear, unsweetened, synthetic flavored juice. Some people even go so far as inferring this muck is necessary in order for NETs to have a full tobacco flavor but in fact this isn't true. The muck is actually a flavor inhibiting, coil/wick trashing contaminant that contributes -nothing- beneficial. It's an unavoidable byproduct of the extraction process.
Mechanical filtration removes any particles of tobacco and other debris from the extract helping to improve its performance. Unfortunately, mechanical filtration is of limited effectiveness in removing the extracted muck. This is because mechanical filtration is good at catching particulates (small particles suspended in the solution) but not good at removing compounds that are dissolved in the solution (solutes). In extracts the solutes (dissolved muck) and extraction solvent form a "homogeneous mixture" that will pass straight through even high retention absolute filters (<1 micron). The only way I've found to remove the muck (without also removing flavor) is by first changing it's state from a solute to a "precipitate" (a separated semi-solid), only then will mechanical filtering be effective at removing it.
When using 190 proof Pure Grain Alcohol (ethanol) as the extraction solvent, a good portion of the muck can be removed through a "freeze filtering" process. This is accomplished by placing the sealed container of extract in a freezer for 72 hours, the colder the temperature, the more effective the process will be. Exposure to extreme cold causes a "precipitation" reaction to occur and over time a substancial portion of the muck will fall out of solution, changing from a solute (dissolved muck) into a "precipitate" (seperated semi-solid muck). As it falls out of solution the precipitate coalesces in the bottom of the container. After 72 hours (and while still in the freezer) the extract is filtered. Here's how much precipitate (muck) was removed from ~50ml of an ethanol based tobacco extract;
For larger batches of ethanol based extract, there's a more effective technique of purification available. It involves freeze filtering "reduced" extract. To reduce an ethanol based extract you simply evaporate a large portion of the ethanol off, the portion that remains is highly condensed. Once reduced the remaining condensed extract becomes oversaturated with solutes making the freeze filtering process even more productive. To illustrate how effective the purification process can be here's what coils and wick look like after vaping (dripping) ~10ml of NET made from highly purified extract;
The most common extraction solvent used by DIY home extractors and retail NET vendors is Propylene Glycol (PG). Neither PG nor VG based extracts can be freeze filtered, however, out of necessity, I did find a way around this. I Mixed a well aged, highly filtered PG/VG based extract with an equal amount of 190 proof PGA (ethanol). I allowed this mixture to sit at room temperature for a day and then placed it in a freezer at -20F. After 72 hours (and while still in the freezer) the extract was filtered. Here's a pic of the muck removed from just 55ml of PG/VG based tobacco extract;
The 80/20 PG/VG extract had already been vacuum filtered through an absolute 1 micron borosilicate glass lab filter so what you see is what mechanical filtration alone couldn't catch without first adding ethanol and then freeze filtering the mixture. You're looking at "the muck" that makes NET so hard on wicks/coils. I don't suggest purifying PG/VG based extracts this way, there's no point since you could just use ethanol for the extraction solvent to start with. I developed this method because I have a lot of well aged PG/VG based extracts made from tobacco that is no longer sold/available. Since these extracts are irreplaceable I wanted to find a way to purify them. After freeze filtering was complete I simply evaporated the added ethanol off and re-filtered the extract through a 1 micron paper lab filter.
