I found a very interesting article here dealing with Citric acid and how/not to use it:
Here is the article, albeit old, it has some fantastic pointers. Be sure to read the comments on the OP.
I accidentally posted this over at DIY_eJuice, oops.
As some of you are aware, I've been spending quite a bit of time and fundage on figuring out citric acid (and malic and tartaric as well).
Over the past year or so, my theory was that the reason for citric acid's efficacy was mostly because it lowered the pH level of the e-liquid -- it made it more acidic. Repeated trial and error of mixing various non-flavor acids into solution showed me I was totally 100% wrong about pH.
A month or so ago, I came across a great research paper on pH in the soft drink industry: "Effect of changes in pH on the release of flavour compounds from a soft drink-related model system" by Hansson et. al -- Sept 1, 2001 in "Food Chemistry" volume 74(4)
This 15 year old paper opened my eyes to something I had never come across before but finally brought to confirmation what I had also never considered: citric acid works on certain flavors because of a molecular interaction between each acid and those specific flavor compounds.
Anyone who has a registered login to my juic.org site will be able to read the entire paper for their own purposes, but since I bought the paper myself I'm not able to release it publicly. For everyone else, here's the run down:
The study monitors just 6 ester aroma compounds:
Also interesting in the paper is that different amounts of citric acid had different effects on different volatiles! Adding a little bit released some of the compounds, adding a lot muted some compounds but released others.
This is a huge piece of research to uncover because it is something that mega compounders already are aware of but the laymen mixers (and smaller e-liquid vendors) probably have no idea about.
Since I cam across this paper, I started to do really really small tests with citric acid in solution -- much smaller than before. The paper tested their own outcome by taking 10mL of water with 0.1% of flavoring (in PG) and then adding 1g, 0.1g, 0.002g and 0g of citric acid and testing headspace for the aroma volatiles.
The 0.002g value showed the greatest overall release of aroma compounds into headspace -- which means if the flavoring was 0.1% of 10ml (let's call it 0.01g of flavoring), then the most aroma release happened at 0.002g of citric acid, or about 0.2% citric acid to flavor and 0.0002% citric acid to overall solution!
These are TINY amounts. MUCH tinier than I had ever played with before.
It appears it might make more sense to measure out citric acid as a percentage against flavor percentage rather than measure it out against the total volume of the solution.
In the past week I've started to super-dilute citric acid even lower than before and definitely have (anecdotally) seen a difference in flavor release.
Also, this paper references some other older papers which discuss apricot AND bakery flavors as seeing usefulness in adding TINY amounts of superdiluted citric acid -- I never tried citric acid with bakery flavors, but will be playing with it this week -- primarily taking OEM premixed bakery flavors and seeing if adding 0.0002% citric acid might make a difference in flavor release.
Regardless of your usage of CA in solution, it does appear that we're just going overboard with how much we use. Note that we do use a LOT more flavor (v/w) than soft drinks do, which means we would also probably use more CA, but nowhere near the values we've been discussing in the past.
Here is the article, albeit old, it has some fantastic pointers. Be sure to read the comments on the OP.
I accidentally posted this over at DIY_eJuice, oops.
As some of you are aware, I've been spending quite a bit of time and fundage on figuring out citric acid (and malic and tartaric as well).
Over the past year or so, my theory was that the reason for citric acid's efficacy was mostly because it lowered the pH level of the e-liquid -- it made it more acidic. Repeated trial and error of mixing various non-flavor acids into solution showed me I was totally 100% wrong about pH.
A month or so ago, I came across a great research paper on pH in the soft drink industry: "Effect of changes in pH on the release of flavour compounds from a soft drink-related model system" by Hansson et. al -- Sept 1, 2001 in "Food Chemistry" volume 74(4)
This 15 year old paper opened my eyes to something I had never come across before but finally brought to confirmation what I had also never considered: citric acid works on certain flavors because of a molecular interaction between each acid and those specific flavor compounds.
Anyone who has a registered login to my juic.org site will be able to read the entire paper for their own purposes, but since I bought the paper myself I'm not able to release it publicly. For everyone else, here's the run down:
- pH doesn't matter.
- Citric Acid and other acids work because they release esters into headspace (this is what creates smell/odor perception)
- Without any citric acid added, the solution releases some esters into headspace.
- With a tiny tiny bit of citric acid added, the solution releases MORE esters into headspace.
- With too much citric acid added, the solution doesn't release ANY esters into headspace.
The study monitors just 6 ester aroma compounds:
- isopentyl acetate
- ethyl hexanoate
- cis-3-hexenyl acetate
- linalool
- 1-menthone
- limonene
Also interesting in the paper is that different amounts of citric acid had different effects on different volatiles! Adding a little bit released some of the compounds, adding a lot muted some compounds but released others.
This is a huge piece of research to uncover because it is something that mega compounders already are aware of but the laymen mixers (and smaller e-liquid vendors) probably have no idea about.
Since I cam across this paper, I started to do really really small tests with citric acid in solution -- much smaller than before. The paper tested their own outcome by taking 10mL of water with 0.1% of flavoring (in PG) and then adding 1g, 0.1g, 0.002g and 0g of citric acid and testing headspace for the aroma volatiles.
The 0.002g value showed the greatest overall release of aroma compounds into headspace -- which means if the flavoring was 0.1% of 10ml (let's call it 0.01g of flavoring), then the most aroma release happened at 0.002g of citric acid, or about 0.2% citric acid to flavor and 0.0002% citric acid to overall solution!
These are TINY amounts. MUCH tinier than I had ever played with before.
It appears it might make more sense to measure out citric acid as a percentage against flavor percentage rather than measure it out against the total volume of the solution.
In the past week I've started to super-dilute citric acid even lower than before and definitely have (anecdotally) seen a difference in flavor release.
Also, this paper references some other older papers which discuss apricot AND bakery flavors as seeing usefulness in adding TINY amounts of superdiluted citric acid -- I never tried citric acid with bakery flavors, but will be playing with it this week -- primarily taking OEM premixed bakery flavors and seeing if adding 0.0002% citric acid might make a difference in flavor release.
Regardless of your usage of CA in solution, it does appear that we're just going overboard with how much we use. Note that we do use a LOT more flavor (v/w) than soft drinks do, which means we would also probably use more CA, but nowhere near the values we've been discussing in the past.
