How carbonation affects flavor and aroma

http://www.sciencedirect.com/science/article/pii/S0022030291783823
Abstract: Raspberry, strawberry, peach, and root beer flavored milks were carbonated at subthreshold, low, and high carbonation levels with mean carbonation volumes of <.60, .74, and 1.42, respectively. The effect of carbonation on perceived aroma and flavor by mouth attributes was determined through evaluation by a trained panel. Panelists detected a significant difference in carbonation intensity between the high carbonation level and the subthreshold and low carbonation levels. Carbonation significantly suppressed cooked milk aroma and flavor by mouth at the low and high carbonation levels, but CO2 significantly enhanced sourness and astringency at the high carbonation level. Chalkiness and bitterness were rated significantly higher at the high carbonation level than at the low or subthreshold levels.

http://chemse.oxfordjournals.org/content/23/4/397.short
Abstract: Previous studies of the effect of carbonation on taste perception have suggested that it may be negligible, manifesting primarily in increases in the perceived intensity of weak salt and sour stimuli. Assuming CO2 solutions in the mouth stimulate only trigeminal nerve endings, this result is not altogether surprising; however, there are neurophysiological data indicating that CO2 stimulates gustatory as well as trigeminal fibers. In that case, carbonation might alter the quality profile of a stimulus without producing substantial changes in overall taste intensity&#8212;much as occurs when qualitatively different taste stimuli are mixed. To address this possibility, subjects were asked to rate the total taste intensity of moderate concentrations of stimuli representing each of the basic tastes and their binary combinations, with and without added carbonation. They then subdivided total taste intensity into the proportions of sweetness, saltiness, sourness, bitterness and &#8216;other taste qualities&#8217; they perceived. The addition of carbonation produced only small increases in ratings of total taste intensity. However, rather dramatic alterations in the quality profiles of stimuli were observed, particularly for sweet and salty tastes. The nature of the interaction is consistent with a direct effect of carbonation/CO2 on the gustatory system, although the possibility that at least some of the observed effects reflect trigeminal-gustatory interactions cannot be ruled Out.

http://www.sciencemag.org/content/326/5951/443.short
Abstract: Carbonated beverages are commonly available and immensely popular, but little is known about the cellular and molecular mechanisms underlying the perception of carbonation in the mouth. In mammals, carbonation elicits both somatosensory and chemosensory responses, including activation of taste neurons. We have identified the cellular and molecular substrates for the taste of carbonation. By targeted genetic ablation and the silencing of synapses in defined populations of taste receptor cells, we demonstrated that the sour-sensing cells act as the taste sensors for carbonation, and showed that carbonic anhydrase 4, a glycosylphosphatidylinositol-anchored enzyme, functions as the principal CO2 taste sensor. Together, these studies reveal the basis of the taste of carbonation as well as the contribution of taste cells in the orosensory response to CO2.

I started a different thread asking the question in the title of this thread but didn't get the answers I was looking for so here are a few scholarly articles on the subject. I find the first one to be really interesting because it states that carbonation affected flavor AND aroma, albeit in flavored milk beverages. I wish I could find some more beer-specific work on the subject.

Enjoy!

More:
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.1992.tb06871.x/abstract
The effects of CO2 level on sweetness and of sweetener level on carbonation perception were measured in two sweetened systems. The effects of CO2 level on sourness and of acid level on carbonation perception were measured in two acidulated systems. The effects were measured at concentrations in ranges of 2-16% (w/v) sucrose, 0.015-0.12% (w/v) aspartame, 0.02-0.29% (w/v) citric acid, and 0.015-0.06% (v/v) phosphoric acid. Little effect of carbonation on sweetness was found in either sweetened system. Sucrose at 16% (w/v) reduced carbonation perception. Carbonation enhanced sourness ratings at the lower acid levels and had no effect at higher acid levels for either acid. No effect of acid level on carbonation perception was found.

http://chemse.oxfordjournals.org/content/16/4/337.short
The objective of this study was to determine the effect of temperature on carbonation perception in carbonated spring water and to determine the influence of the degree of panel training on this effect. Spring water was carbonated to two carbonation levels, 2.4 and 3.0 volumes CO2. The samples were served at 3, 10, 16 and 22°C, and evaluated by both trained and naive panels. Two assessing conditions, swallowing and expectoration, were employed to rate samples. Carbonation intensity was perceived to be higher at lower temperatures than at higher temperatures, even after having taken into account the fact that there was less CO2 in the samples at higher temperatures. This effect held true for both naive and trained panels. The temperature effect on carbonation perception was carbonation level dependent; differences were more evident at the higher carbonation level.

Yikes -- this is fantastic. I just posted a (very unscientific) question about carbonation/carbonic acid and "sour" flavor here:

https://www.homebrewtalk.com/f128/low-mash-ph-results-sour-taste-128883/index2.html

BTW -- after reading just the abstract from the first one, I'm thinking that my own sourness in my finished beers might result from slight overcarbonation (something not immediately perceptible in the mouthfeel or the look -- but now I'm wondering if cut back the priming sugar slightly, I'll actually lose little in the carbonated mouthfeel but perhaps gain quite a bit with decreased sourness. I'm interested, too, in the idea of increased bitterness at higher carb levels.)

At any rate, this carbonation discussion is not something I've come across too often in all my forum reading. I read about overcarbonation and undercarbonation -- and the usual questions about what levels are appropriate to what style -- but not too much about the actual sensory impact of carbonation -- at least not as it relates to pH of the finished beer (which is my question with the above link).

As an aside, it's interesting to note that while pH control -- or attempted pH control -- at a homebrew level often results in better tasting brew it also opens up a pandora's box of additional questions and concerns and possibilities.

I wasn't able to find much on here either so hopefully this thread will get the discussion going. I think it's something that's overlooked but, based on the papers I posted above, getting your carbonation levels right can make a significant difference in your beer. I'm glad someone else is interested!