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Aroma Chemistry

Why Does Bacon Smell So Good? – The Aroma of Bacon

Aroma Chemistry – The Aroma of Frying Bacon
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Aroma Chemistry – The Aroma of Frying Bacon
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When it comes to breakfasts, there are few aromas better than that of bacon, sizzling and crisping in a pan. As part of a brief new series looking at the chemicals behind aromas, this graphic considers the chemicals that lend bacon it’s characteristically mouth-watering scent.

Considering that bacon is such a universally worshipped food item, you’d’ve thought research on anything relating to bacon would be a hot commodity. The world of scientific research doesn’t seem to be quite as enamoured with bacon as the general public, however, and research on the compounds behind the aroma of frying bacon is surprisingly sparse. Clearly science has a few priorities to get in order.

After some rooting around online, I was able to turf up one fairly detailed study, however. In this research, scientists tried to discover the compounds that give frying bacon its aroma, by comparing it with the aromas released when cooking pork loin. They did this by frying the meat, mincing it, then passing nitrogen gas over it to collect any volatile organic compounds that were being released. The collected volatile compounds were then passed through a gas chromatograph and mass spectrometer in order for identification to be carried out.

The volatile compounds collected originate in part from the Maillard reaction, in which sugars in the foodstuff are broken down by reaction with amino acids as heating occurs. In bacon, other volatile compounds are produced due to the thermal breakdown of fat molecules. As well as this, in the case of smoked bacon, nitrite used in the curing process can also react with the fatty acids and fats present in bacon on heating – this leads to a higher percentage of nitrogen-containing compounds than in standard pork meat.

So, what compounds give bacon its aroma? The researchers compiled an exhaustive list of the volatile compounds present; they found that hydrocarbons, alcohols, ketones and aldehydes were present in large quantities in both the bacon and pork aromas. They also found some compounds present exclusively in bacon, and suggest that these play a major role in its scent.

These were all nitrogen containing compounds; they included 2,5-dimethylpyrazine, 2,3-dimethylpyrazine, 2-ethyl-5-methylpyrazine and 2-ethyl-3,5-dimethylpyrazine. The researchers found that, individually, none of these compounds had the precise smell of bacon – however, they suspect that, combined, and in combination with other volatile compounds, it is most likely that they are responsible.

As well as these compounds, compounds which had previously been identified, from other meats, as having a ‘meaty’ scent were isolated. These included 2-pentylfuran, an oxygen-containing organic compound, and 3,4-dimethylpyridine, another nitrogen-containing compound. Although unsurprising, it’s perhaps a little disappointing that it’s not a lone compound that is responsible for bacon’s aroma; however, the difficulty in ascribing the origin of the smell hasn’t stopped the attempts of some to capture its essence in perfume form…

EDIT: Reactions, the American Chemical Society’s YouTube channel, made a short video based on this graphic, which you can view right here.

An edited version of this graphic and article will appear in the upcoming graphical book on the chemistry of food & drink, available to pre-order now!

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48 replies on “Why Does Bacon Smell So Good? – The Aroma of Bacon”

This is so embarrassing as an active member of ACS. This story is based on one manuscript in a non-ACS journal from 2004 (certainly not new) and was further being picked up by NPR. If any one with remote understanding of flavor chemistry had been consulted, this would have look quite different, been more accurate, and more meaningful. Thumbs down!

I can only work with the available research – this paper, whilst it may not have been in an ACS journal, was still in a peer-reviewed journal, and the research methods seem to be sound. I’ve also been in contact with several flavour chemists, none of whom have flagged any concerns with the content of the graphic or the article. The graphic, and the research for that matter, does not presume to state that the research is categorical, or that specific compounds can be precisely pinpointed. It does, however, point to likely contributors, which this article reflects. I’ve also never claimed the research was new – I can’t help the inferences of news outlets!

If you have any further information you can contribute to improve the information in the graphic or in the article, then that would be fantastic, and I’d be keen to alter the post here to incorporate it. As it is, your comment simply comes across as rather snide and unconstructive.

We have reached out to ACS to discuss how the professional leadership (members) can support the media in accurately depicting chemistry in the news. Hopefully we can establish better alignment. I believe all of us who publish understand that there will be misrepresentations and that the peer review process is not perfect. And technology changes. Two ways to help avoid misrepresentations are: use more than a single manuscript for reference and look at recent publications, especially in an area that is so rapidly changing as demonstrated by the Nobel Prize being awarded to Linda Buck and Richard Axel in 2004 for work publishing in 2001 on understanding the multidisciplinary aspect of flavor chemistry (chemosensory sciences).

Thanks for taking the time to write a more constructive response, both here and on the NPR site. I would say that I don’t think the graphic and article here misrepresent the research they are based on. I do agree that the evidence would be stronger with more than the one study, however – I did attempt to find other, more recent studies on bacon, but this was the only one I could track down. You mentioned on the NPR site that “a review of the current literature reveals the number is probably far fewer than 150” – does this mean that you’ve managed to track down something more recent? If you have, it’d be great to edit the article and graphic to reflect this.

My purpose in making the graphics on the site is to communicate the everyday side of chemistry with students, as well as more generally. Obviously, I want to information represented to be as accurate as possible, and I do usually spend a fair amount of time trawling through the research myself, as well as getting others to check the information I’ve researched. It’d be great if you could get in contact via the site’s about page, so that we could have further discussions via email, to ensure that the site content is as accurate as possible with respect to the flavour chemistry side of things. Hope to hear from you!

As mentioned ACS has been approached on how to better utilize the professional membership of the Agricultural and Food Chemistry Division in order to communicate related chemistry in an accurate manner. I do not agree that this “graphic” communicates anything meaningful about the “everyday side of chemistry”. It totally lost site of the fact that flavor chemistry is not just about the chemicals, but must also factor in the human response.

I do not see what chemistry knowledge of value is being communicated through this graphic. What I interpret as the central point of the graphic – “there are a relatively large number of chemicals that make up the aroma of bacon (or any food)” provides no value. The fact that many chemical compounds are present, yet only a few actually contribute to the aroma is one of the first things taught in any introductory course on flavor chemistry at most reputable universities (e.g. U Florida, Cornell, U Minn, UC Davis, UC San Diego, U Nottingham, Tech U Munich, etc) and in the ACS run Flavor Research Workshop. Actually this fact has been assumed to be so central that it may not have even been covered in the last ACS Flavor Research Workshop in 2010

The review of recent studies – numerous review articles, ACS short course, and ACS symposia – and generally the flavor chemistry literature since the advent of CharmAnalysis and AEDA in the 1980’s reveal that no food aroma (bacon or otherwise) is driven by anything nearly on the magnitude of 150 compounds. Even if all 150 compounds extracted from the headspace were able to activate a perception in the human (activate an olfactory receptor), which is rather unlikely, so many other factors would enter into the equation. This is a basic premiss of flavor chemistry –
not specific to bacon. This is what it is so disturbing about this
misrepresentation of the most basic concepts in the area of flavor chemistry.

My review of this graphical communication still gets a resounding 2 thumbs down from me, more if I had more thumbs, for content. It is pretty though.

I guess my main point is, I resent the use of “ACS”‘s name and reputation to represent “science” that did not even originate from an ACS source and has not received vetting through actual ACS professionals in the expertise of the research. Further, isn’t there enough interesting work published in the last few years, not to have to dig something up from a decade ago? The reputation of ACS is central to our mission statement.

I think you’ve become a little confused over the content of the graphic. It clearly states that there were 150 volatile compounds given off from cooking bacon in the study – it does NOT claim that all of these contribute to its aroma. I’m disappointed that you don’t have a further reference to add to that which I had found – as I stated I can only work with the research available, and I think that the graphic and article accurately represent this research. Even the research itself doesn’t claim all 150 contribute to the odour, it merely identifies some LIKELY contributors – as reflected here. As this is primarily a chemistry blog, I’m focused on the chemical molecules present.

I would hasten to add that this graphic and post HAVE been seen by other flavour chemists (including some at one of the institutes you’ve mentioned), who have not found fault with it. Also, it was the ACS who approached me to use the subject of this graphic in their video. You’ve surely realised that this site focuses on explaining everyday chemistry; it’s not a new research news portal by any means. I think that the graphic, and the ACS Reactions video, have done a fantastic job of getting people interested in chemistry, which I think can only improve the standing of the ACS. It’s as much about the public reputation as the reputation amongst chemists, and I think that’s something you’re overlooking. Other flavour & food chemists I’ve spoken to have been enthusiastic about the potential of the site’s food graphics to enthuse students about chemistry – I’m sorry you don’t feel the same way. Your attitude to science communication I’m afraid gets a comparable number of thumbs down from me.

Having done some detective work, I’m aware you certainly have far more experience and knowledge in the field of flavour chemistry than I, so I’m a little disappointed that you haven’t taken up my offer to communicate further and in more detail via email. As such, unless you’re willing to engage constructively in such a manner, I’m going to consider this conversation closed.

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Hello! I’m using this article as a resource for a class presentation on aroma chemistry. Would you mind explaining in simple terms the chemistry behind how Nitrogen Gas is able to capture or collect all the volatile compounds from the minced meat?

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