The Chemistry of Whiskey

"Understanding the delicate interplay between chemistry and aroma could be a huge help to distillers looking to tweak their whiskey to encapsulate that perfect blend of smoky and spicy….It’s research that means that the perfect whiskey–smoky, spicy, or however you want it–might not be so elusive after all."(2)

Inside the Jack Daniels Distillery

This Thanksgiving, as per usual, I'll be making the long overland journey to Nashville to see my brother. Although the visits are, of course, enjoyable the question always arises among my  family: what on earth are we going to do for four days while we're not stuffing our faces? This year, it looks like we're taking a tour of the Jack Daniel's Distillery in Lynchburg, TN.

My immediate reaction to this was, I bet they have a lab. Then, I wonder if they're hiring? Well, like most companies which produce alcoholic beverages, they do indeed have a lab and a fairly extensive one at that.

According to an article in the New York Times the use of high-tech analytical chemistry equipment and techniques wasn't fully implemented at the company until 2002, 136 years after it's founding. Sensory scientists were concerned that not all the key aroma compounds of their whiskey had been identified and that therefore there could be room to improve its taste (if not by changing the formulation then through ensuring the balance of compounds is perfect for each and every batch). This new research into their own product went as far as analyzing the effects of the type of oak used for aging barrels (1).

Whiskey Lactone: β-methyl-γ-octalactone

The basic process for making whiskey starts with fermentation of a blend of corn, rye, malt and barely. That product runs through several feet of sugar maple wood charcoal, is distilled, and allowed to age in an oak barrel (usually for years). Interestingly - well, there's two really interesting things here - the charcoal removes the esters from the whiskey making it less fruity and pungent, and the distillate leaves behind a material with upwards of 500 unknown compounds, some of which might be aroma or flavor chemicals. When this chemical mass was sifted through for potential whiskey additives, scientist's at Jack Daniels "identified 28 critical compounds that seemed to give the most flavor to the bourbon, including beta-damascenone, which give the taste of cooked apples; lactones, which provide coconut flavors and eugenol from the oak barrels, which give clove like flavors" and "when the 28 compounds were added to the alcohol and other compounds, the result was a pretty good bourbon" (1).   

Similarly, a Smithsonian Magazine article divulges the chemical complexity of whiskies in general. A University of California, Davis researcher (Tom Collins) and his team analyzed 60 American whiskies and found over 4,000 different non-volatile compounds in total, many of which overlapped among the brands and types. Because whiskey is made from a variety of grains and because yeast is involved there is an overwhelming number of potential chemicals that can be produced during the process (2). 

The purpose of the research was to answer on a fundamental level the question: why are all bourbons whiskey but not the other way around? The team found a more technical answer than production regulations can supply, "there are 50 to 100 chemical compounds such as fatty acids and tannins that can be used to distinguish a Tennessee whiskey from a bourbon" (2). 

An article from the Royal Society of Chemistry gets into the fine details and complexities of Scotch Whiskey production. The Scotch Whiskey Research Institute in Edinburgh, Scotland delves into the chemistry behind Scotch whiskey as its own class of liquor with its unique flavor and aroma compounds. 

Like most liquors scotch whiskey contains many of the major classes of flavor chemicals: fatty acids, aldehydes, esters, and more. Unlike Tennessee whiskey, the only raw material involved is barely (becomes malt upon fermentation, hence "malt whiskey") so the flavor combinations from starting materials is relatively limited. However, traditional scotch production has some interesting conventions: smoking the aging barrels over a peat-fire, the use of copper stills, and aging in oak barrels for 12 to 16 years. 

The complexities of peat-smoke is practically a field on its own: one study found that peat in different locations around Scotland produced a different chemical profile (4). Like dripping the undistilled brew through sugar maple wood charcoal in Tennessee whiskey production, the firing of the casks produces a layer of active carbon which removes undesirable chemicals. Additionally, lignin from the wood breaks down during ethanolysis which produced aromatic aldehydes and whiskey lactones which are often fruity and even coconut-like (3). 

Peat Site in the Shetland Islands

Like the charcoal, the use of a copper still reduces the amount of sulfur compounds that end up in the final product. Although these chemicals are important to produce meaty flavor, as noted in last week's post, no whiskey purist wants their drink to taste like turkey (3). 

The type of barrel used for aging also has effects on the product. Bourbon producers and some Tennessee whiskey producers like Jack Daniels only use their oak casks once before selling them to other companies (which seems incredibly wasteful to me…). Casks from different alcohol production processes effects the Scotch whiskey. For example, if rum or sherry casks are re-used, the whiskey will be darker and sweeter. More important than the type of cask used, however, are the reactions that occur when the liquor in is contact with the wood. These include the absorption of dimethyl sulfide into the wood, reducing the pungency of the final product and the oxidation of alcohols and aldehydes to form characteristic esters (3). 

Based on the articles I read it seems that the chemistry and complexity of whiskey is something that has only recently been deeply explored. It's left me wondering how much research has been done on other liquors and the various processes that go along with them. Wine, of course, has been extensively studied for some time but the in-depth analysis of flavor and aroma compounds of other alcohols are potentially just as intricate yet not fully understood or even appreciated. 

If you want to know everything ever about Scotch Whiskey production, here's a documentary narrated with an excellent accent. 

And for kicks, here's your holiday guide for whiskey tasting. 

Ashley 

1. Chang, Kenneth. "What's in that Bottle of Jack Daniel's? A Chemistry Mystery." The New York Times (Archives), Nov. 5, 2002. Web. Accessed Nov. 23, 2014.

2. Geiling, Natasha. "How Chemistry Can Explain the Difference Between Bourbon and a Tennessee Whiskey." Smithsonian Magazine Online. Sept. 9, 2013. Web. Accessed Nov. 23, 2014.

3. Gills, Victoria. "A Whiskey Tour." The Royal Society of Chemistry "Chemistry World." December 2008. Web. Accessed Nov. 23, 2014.

4. B Harrison et al, J. Inst. Brew.,  2006, 112, 333  

Thanksgiving: A Food Chemist's Holiday

With Thanksgiving rapidly approaching you're surely interested in knowing the science behind roasting the tastiest turkey. The Maillard reaction is one of a few fundamental chemical processes that relates to cooking. While I've long been aware of this I've never delved deeper than casually noting that it causes the browning of toast and the dark streaks on grilled food. Besides changes in appearance the reaction involves a number of well-documented chemical steps that result not only in the darkening of food but also the formation and release of aroma compounds. Just think about this: does raw meat have the same flavor as grilled? Right. So, that's a very clear example of just how much the Maillard reaction affects what we eat.

Raw fish does NOT taste like cooked fish

Just over a hundred years ago Louis Camille Maillard wondered what could make cooked food turn brown and release carbon dioxide. Although he was unable to discover the specific mechanisms involved he did realize that the reaction produced a class of previously unknown compounds which he called melanoidins, i.e. compounds that are produced through a reaction of sugar(s), amino acid(s), and heat.

Louis Camille Maillard

The reaction itself has now been illustrated in a variety of ways. In The Chemistry and Technology of Flavors and Fragrances Liam O'Hare and John Grigor chose to represent the process as the simplified  scheme proposed by John Hodge in 1953. His schematic goes something like this:

A carbonyl group, such as glucose, and an amino compound, such as lysine or glycine, react when heated together. Condensation occurs to produce a Schiff Base. A glycosylamine forms and either an aldose or ketose results. If an aldose forms the Amadori rearrangement creates an unstable intermediate while when a ketose forms the Heyns rearrangement leads to an unstable intermediate. The next step in either case is a dehydration followed by a deamination leading to a variety of flavor and aroma products like furans and thiazoles.

Hodge Schematic from The Chemistry and Technology of Flavors and Fragrances

In this system, water acts as a mobility-enhacing solvent. Additionally, analogous reactions can occur with thiols. Sulfur-containing compounds, while acrid or foul-smelling in high concentrations, are surprisingly critical to flavor of cooked meat.

I found this video helpful in understanding the reaction: 

And that brings us back to Thanksgiving. Why does only the surface of a roasted turkey turn that gleaming golden-brown color? That's due a different - but also important - reaction: caramelization. When sugars are heated above 150 degrees Celsius, anhydrides form. All meat contains ribose and therefore sugar is available for a reaction to occur. The high temperature and lack of water on the surface of say, a turkey in the oven create ideal conditions for caramelization. The anhydrides break down into furfural or 5-hydroxymethylfurfural and with continued application of heat become furans, aldehydes, ketones, aliphatic and aromatic hydrocarbons. Some furans present in cooked meat are critical to their flavor. For example, bis-2-methyl-3-furanyl is a key "beefy" component and has one of the lowest odor thresholds known being detectable at 0.00002ppb.

White on the inside, browned on the outside: caramelization 

"Flavor moderators" also impact the taste of cooked meat. The degradation of phospholipids leads to fatty aldehyde - key components of "meaty"flavor - formation. One experiment to prove their importance extracted all the lipids from a piece of meat and upon cooking the lipid-less tissue a biscuit-like smell was produced.  A high proportion of fatty aldehydes limits the production of heterocyclic aroma compounds during cooking (i.e. the Maillard Reaction).

There's a balancing act going on at the chemical level: too many high-impact aroma compounds can cause strong and unpleasant sulfurous odors while too few aroma compounds will leave your turkey tasting like the biscuits it's served with.

Ashley



Sources

"100 Years of the Maillard Reaction: Why Our Food Turns Brown," J. Agric. Food Chem. 2013. 61. p.10197. http://pubs.acs.org/doi/pdf/10.1021/jf403107k 

Hodge, John. "Chemistry of browning reactions in model system." J.Agric. Food Chem. 1953, 1, 928−943.

Rowe, David J (ed.) (2005) Chemistry and Technology of Flavors and Fragrances. Blackwell Publishing: Poole. Ch.3.

News Review: Pumpkin Spice

"Retail sales of pumpkin offerings have experienced double-digit growth for the past several years, reaching nearly $350 million in 2013, according to market research firm Nielsen. And that figure doesn't count Starbucks pumpkin spice lattes…." 

Carmen Drahl, C&EN 

I admit to hoarding Chemical and Engineering News (C&EN) articles that mention flavors or fragrances. Or food additives. Or food regulations. Pretty much anything that mentions chemicals and things consumers consume. In addition, I recently discovered - to my joy - a section of their website called "What's That Stuff" (which is also the header of certain articles in the magazine).

I'm far from the first and surely far from the last to bring this topic up, but the most recently featured stuff was the (in)famous "pumpkin spice flavor" in the October 27 issue. According to this article the complexities of natural flavorings don't necessarily need to be present for the human brain to understand what a flavor is meant to be. "Pumpkin spice" is considered to be a mixture of spices containing around 340 flavor-relevant compounds. However, given just a fraction of those compounds and concentrating on the inclusion of key aroma and flavor molecules - about 15-30 components of the spice mixture's complete profile - the overall taste is interpreted as true-to-nature by the consumer.

I wrote a blog post on another website on Natural and Artificial Flavors where I basically concluded that both have their pros and cons but that artificial flavors aren't any "scarier" their "natural" counterparts. That said, there's a lot more that goes into making the perfect product that isn't flavor related. Take, for example, that famous Starbucks Pumpkin Spice Latte.

Is Your Coffee Toxic?

Sugar, preservatives, coloring. There's probably even some sensation-generation molecules in the mix. Things to make warm and cozy feelings all over your mouth. The above info-graphic might be exaggerating a bit about the side effects but then again….

But I digress.

I wanted to tell you about the main chemicals involved in pumpkin pie spice according to this article in C&EN. Zingiberene (ginger), (E)-cinnamaldehyde (cinnamon), sabinene (nutmeg), eugenol (clove) and possibly cyclotene (maple or brown sugar flavor) and - everyone's favorite -  vanillin. Other, smaller contributors to the wildly popular pumpkin spice flavor include allspice, anise, and mace. Find their mug shots below….(thanks to Wikimedia Commons for having awesome drawings of chemicals and pictures of foodstuffs). In addition to the images, definitely check out this resource from NBC to learn more about the molecules in these spices.

Zingiberene

(E)-cinnamaldehyde

Sabinene

Eugenol

Cyclotene

Vanillin

Just as the pictures I've paired with the chemical names show very different things than what the chemicals themselves are, key flavor compounds are representations of the full flavors found in nature. Like the images these critical components of a flavor are enough to give the brain context and therefore understanding for something that is as poor a representation of the true thing as still, flat drawings of an-ever-moving molecule. Pretty tricky on the food industry's part, don't you think?

All of this begs the question: what aroma compounds are actually in a pumpkin? As it turns out real pumpkins, like, the kind from a vine in a patch contain a very different set of aroma compounds. If you've ever taken a bite out of a pumpkin at Halloween (anyone?) you'll recognize that they aren't sweet and have a subdued not-all-that-appealing flavor.

According to this article in Scientific American, pumpkins smell like vegetables or squash (not surprisingly) because of "leaf alcohol" or cis-3-hexenol. Other major flavor and fragrance compounds include 2-hexenal, diacetyl, 2-meythlbutanal, furfural and pyridine.

Credit: "Pumpkin, Hold the Spice" Scientific American
Clockwise, from top left: cis-3-hexenol, diacetyl, 2-methylbutanal, furfural, pyridine

This is a good chance to look at some of these totally natural molecules and get some perspective. Things created in labs aren't necessarily more harmful than things created by plants. I mean, take water hemlock, for example (my go-to for putting nature on the spot).

This isn't to say that all chemicals made in labs are fine and dandy. In fact, there are loads of problems with chemical formulation and manufacturing due to waste, toxic materials usage, and more. But both sides of the natural/artificial arguments have their pros and cons. Take diacetyl, one of the chemicals found in pumpkins. It's responsible for the buttery aroma of pumpkins when it occurs naturally and is harmless. However, in its pure form - or in large quantities on microwave popcorn - it poses a risk of severe lung disease.  Pyridine is another chemical mentioned above and it's commonly used as a solvent in the lab which is certainly not something you'd want to ingest.

So, in conclusion, while pumpkin spice flavors might not contain any real pumpkin they do contain some of the key aroma compounds from the spices they're supposed to represent. And while this might be an unsatisfying answer for consumers the chemicals used are simply mimics of things found in nature. In short, I'll continue to eat my pumpkin spice oatmeal, thanks very much.

Ashley

Theories of Odorant Structure-Function Relationships: The Future for Designing Fragrance Compounds?

“Perfume is decidedly not about two things: it isn’t about memory and it isn’t about sex. Perfume is about beauty and intellect. A perfume is a message in a bottle—not a smell—and the message is written by the perfumer and read by the person who smells it.”¹

"I think everyone (scientist or not) at some point wonders how smell works. The Italian physicist Giorgio Careri told me that Enrico Fermi in his presence once sniffed the air while frying onions and said “wouldn’t it be nice to know how that works?” I started reading up on smell and it gradually became clear to me that there were big gaps in our knowledge, so I started thinking about it."2

-Luca Turin

Upon getting back into the Chemistry and Technology of Flavors and Fragrances text, I discovered (via Chapter 11) just how much we don't know about how to design odorants. The discovery process of flavor and fragrance molecules throughout history has been haphazard and involving a great deal of luck. The author of this section identifies one of the main methods of finding novel odorants as "Serendipity." While humorous, the fact that scientists consider this a legitimate method for finding new compounds is telling of how little we actually understand the process. It's funny to see how differently contributors to this book speak about our level of understanding of the olfactory system; in this section, internationally recognized biophysicist and perfumer Luca Turin presents two major theories - stress: theories - behind rational odorant design: vibration and shape.

In 1946, Linus Pauling suggested for the first time that the shape of molecules affected their function. This idea has proved to be critical to chemistry but when applied to the flavor and fragrance industry it doesn't always pan out. If the character of odorants relied entirely on their structure they could be designed just like pharmaceuticals. Unfortunately, it's more of a trial-and-error process. In the first place, there's a lack of understanding about the exact structure of olfactory receptors. Receptor antagonists, for example, are important in pharmacology for turning receptors "off." No odorant has been found to do this which means there's something amiss in our comprehension. The olfactory receptors must be somehow different than those that absorb drugs. Additionally, there are a number of  little contingencies like the fact that we can accurately identify functional groups no matter what the rest of the structure looks like. In every case, "rules" about structure-character relationships are broken; catalogues which have tried to place odorants into structural categories are essentially "catalogues of exceptions." 

The counter-theory is that molecules with similarities in vibrational spectra should be similarly perceived by the nose. It should be noted that Turin believed pretty ardently in this theory, even to the point of founding a company called Flexitral, Inc. based on the concept. This theory is supported by evidence of things like boranes and thiols: IR spectra shows that they exhibit the same frequency range and they also smell a lot alike. However, chemically they're completely different…so there's another mystery. Vibration theory only accounts for odorant character so the cause of varying intensity of odorants remains mysterious. Additionally, no one has proven that receptors can respond based on vibrations of molecules and the theory is essentially untested at this point. 

Both theories have their strengths and weaknesses (there's a lot more to them than what I've summarized here). It's possible that human olfaction operates through a combination of both theories, or something altogether different. What was most astounding to me about this chapter is that we understand so poorly something so commonplace yet we're crashing protons together and trying to identify the tiniest bits of matter that seem so distant from our day-to-day reality. That's certainly not to say one area of study is more important than the other, simply that there's an incredible amount that we don't know. With continued research, it's possible we'll find some of the answers right under our noses.

Ashley
1 Suhrawardi, Rebecca. "Style.com/Arabia Pulls Fragrance Legend Luca Turin As Its Fragrance Critic," The Fragrance Foundation Jan 7, 2014. Web. Accessed Oct. 28, 2014.

2 Sinatra, Nina. "Opinion: The Science of Smell; Luca Turin on the Vibration Theory of Scent," The Tech, Online Edition. Massachusetts Institute of Technology: Cambridge, Massachusetts. Apr. 23, 2010. Web. Accessed Oct. 28, 2014. 

3 Rowe, David J (ed.) (2005) Chemistry and Technology of Flavors and Fragrances. Blackwell Publishing: Poole. Ch.11.

Modern Science Writing: A Reflection and Reading Reaction

For this post, I'm going to completely change gears. I've been writing on the Chemistry and Technology of Flavors and Fragrances, but earlier this week I read about a hundred pages from a very different kind of text: The Oxford Book of Modern Science Writing. This book is a collection of extracts, articles, criticisms, poetry, and more from well-known scientists of the twentieth century (everyone from Albert Einstein to Primo Levi), seamed flawlessly together by its editor, Richard Dawkins.

When I finished the last chapter I read ("Who Scientists Are"), and carefully slipped the book back into my bag it felt like one of those moments up to which my whole life has been leading. I've spent a lot of time with my face pressed against textbooks, hoping the knowledge would sort of find its way from the pages through an unknown channel of skin and cell membranes and nerves channels, eventually sticking itself into my memory. I've spent a lot of time wondering why I chose to major in chemistry. What I'm going to do with it, if anything. What I was thinking, if it's worth the stress. If my math skills will inhibit me. If my dreams, as they often have been, will always be bigger than the operating budget and more time-consuming than I can afford.

That said, I've been granted more than my fair share of opportunities. But I've suffered from what I imagine to be a fairly common disillusion about studying science: the idea that learning the secrets of life will be all fireworks and miraculous, Nobel-prize winning discoveries when in reality it takes patience, failure, and compromise. Even though when I set off I knew it would be a difficult path to follow, I didn't comprehend the gaps in knowledge that would cut me off at every turn and have me confused, turned around and frustratingly rummaging in the woods. It seems that after almost three-and-a-half years of studying the subject, I remain hopelessly clueless about it.

Then, there's the whole other branch of that inner argument I mentioned above: I love art in general and poetry in particular. Can those worlds really mesh or will pursuing one inevitably draw me further and further away from the other? Is it a fantasy to think I can do both well?

Here in this book though, the highlighted scientists have an incredible faith in curiosity and the imagination. Many of them - including a number of actual Nobel-prize winners - reflect on their personal difficulties in certain subject areas, their doubts, resource limitations, judgements from others, and more than anything gratitude for what they consider simple good luck (see page 195, Maitland Edey and Donald Johanson's reflection on a chance finding of Lucy in Ethiopia and on page 229 where there's a quote from James Watson, "All through my undergraduate days, I worried that my limited mathematical talents might keep me from being more than a naturalist….there seemed no choice but to tackle my weakness head-on….[math] soon became rather satisfying, even in the age of slide-rules, instead of a source of crippling anxiety").

They have much to say about art. Many of those featured are themselves artists: poetry, short stories, music. Carl Sagan, who I personally admire, wrote spectacular prose (it might make me tear up a little every time I read some). Dawkins says in his introduction to an excerpt from The Demon-Haunted World "open any one of [Sagan's] books and you need go no further than the Table of Contents to experience the tingling of the poetic nerve endings that will continue throughout the book" (239). Just pages before this, before a poem written by Julian Huxley, Dawkins remarks, "I have long thought that science should inspire great poetry, but scientists have published disappointingly few poems" (234).

There are too many great excerpts in this chapter on "Who Scientists Are" to summarize them all, but I figured I could make an attempt to concentrate this book, which is kind of a summary itself, into some of my favorite lines (the most heavily underlined, numerously starred, exclamation point-adorned sentences). One quotation from each of the extracts in this chapter will be listed below. They're words that inspire me, say something I think is really profound, and/or exemplify the kind of person I think I could be (in addition to being quotations able to stand outside the context).

No, I didn't include the authors or the works from which these quotes are specifically excerpted. But as I said, I hope they stand on their own and I hope anyone who reads them says, "wow this book sounds amazing I'm going to go read it." As I prepare to go out "into the real world" with a background in chemistry, a passion for art, and many doubts I can't imagine something better to draw from than a book that, to me, seems like the purpose and justification of science, distilled.

(Page number: "quote.")

156: "Generosity and imagination were, for once, awarded in full. This is a story of human virtue."

161: "How could one seriously believe that the electron really cared about my calculation, one way or the other? And yet the experiments at Columbia showed that it did care…Why it is so, why the electron pays attention to our mathematics, is a mystery that even Einstein could not fathom."

167: "I think we believe that whenever we see an opportunity, we have the duty to work for the growth of that international community of knowledge and understanding…with our colleagues in other lands, with our colleagues in competing, antagonistic, possibly hostile lands…"

171: "She pursued her crystallographic studies, not for the sake of honors, but because this is what she liked to do….at scientific meetings she would seem lost in a dream, until she suddenly came out with some penetrating remark, usually made in a diffident tone of voice, and followed by a little laugh, as if wanting to excuse herself for having put everyone else to shame."

178: "But more incisive than the question, What right have we to form inductions? is the question, How do we form them? [David] Hume gave no explanation of this except habit."

183: "People who write obscurely are either unskilled in writing or up to mischief."

189: "There is poetry in genetics which is more difficult to discern in broken bones, and genes are the only unbroken living thread that weaves back and forth through all those boneyards…it is easy to forget that human fossils remained virtually unnoticed until Darwin."

192: "'It just looked interesting.'" (An archeologist's comment on how he picked the nondescript gully wherein the first Homo erectus fossil was found)

196: "I felt a strong subconscious urge….I am superstitious." (Another archeologist, remarking on the morning of the expedition when the skeleton of Lucy was unearthed)

206: "We who lack an appreciation of history have so little feel for the aggregated importance of small but continuous change scarcely realize that the very ground is being swept from beneath our feet; it is alive and constantly churning."

214: "Suddenly - and how exciting it is when it happens - something will go right and give one a flash of insight into how things work."

219: "There seemed to me an integrity, an essential goodness, about a life in science, a lifelong love affair. I had never given much thought to what I might be when I was 'grown up' - growing up was hardly imaginable - but now I knew: I wanted to be a chemist."

225: "We are coded differently [than social insects], not just for binary choices, go or no-go. We can go four ways at once, depending on how the air feels: go, no-go, but also maybe, plus what the hell let's give it a try. We are in for one surprise after another if we keep at it and keep alive. We can build structures for human society never seen before, thoughts never thought before, music never heard before."

227: "Much better to be the least accomplished chemist in a super chemistry department than the superstar in a less lustrous department."

231: "He gazed at the model, slightly bleary-eyed. All he could manage to say was 'It's beautiful, you see, so beautiful!' But then, of course, it was."

233: "Science often explains the familiar in terms of the unfamiliar." (which is often exactly what poetry does)

237: "In my view, it is the most important function of art and science to awaken this [cosmic religious] feeling and keep it alive in those who are receptive to it."

And finally,

243: "When we shy away from it because it seems too difficult, we surrender the ability to take charge of our future."

On a final note, I started wondering after reading this chapter: at what point can I say that I'm a scientist? Now, I admit that's kind of a fluffy philosophical question. But I was thinking - and maybe this is a product of reading too much Sagan - are we all born scientists, curious about the world and eager to investigate? There's a lot of discussion out there about interest in science waning significantly during adolescence due to poor teaching, peer pressure, and perceived difficulty.
Is the question that should be asked, "at what point is one no longer a scientist?" if the chosen path leads elsewhere? Neil deGrasse Tyson doesn't have a segment in this book but said once - and it's one of my favorite quotations of all time - "In whatever you choose to do, do it because it's hard."

These are the kinds of things I want to keep in mind when taking a terrifying step in life whether that's starting a job, or moving to a new place, or leaving this beautiful little brick bubble.

Ashley

Overview: From Fruit to Flavor

This might sound odd, but I think it would take me a very, very long time to get bored from reading about the development of the flavor industry. This week, I’ve been reading about flavor applications. Everything from the history of the analytical methods used to the gritty technical details of getting the most bang for the bite. As I’ve mentioned previously in this blog, flavors were first commonly synthesized and purified during the mid-nineteenth century, i.e., the Industrial Revolution. However, flavor compounds were not identified and tinkered with by chemists en masse until the invention of gas-chromatography mass-spectrometry (GC-MS) in the 1950’s.

GC-MS Diagram

 Not only did scientists identify and isolate many compounds that they were already peripherally aware of: they also discovered novel flavor and fragrance chemicals, including some of those sensation-causing ones I’ve been rambling on about. Critically, it was determined that flavor is dependent on key aroma compounds - molecules which must be present in order to for a certain taste to result. 

n-decanal

(wikimedia commons)

For example, it was found that n-decanal must be present for an orange to taste like an orange¹.
 Although there are other chemicals present that affect an orange’s flavor, even with their nature-designed uniquely balanced proportions, in the absence of n-decanal an orange just won’t taste right. Pretty nifty. 

In the mid-1970’s, sprectral data from GC-MS was computerized. Yay, digital revolution. Data collection went from counting signals by eye, determining the abundance of signals on UV paper, and comparing the signals present to tabulated collections of compounds. Sounds like not-fun. But it makes me infinitely grateful for the technology I have now. In ten years (or sooner?) we’ll probably be able to tell a computer what was mixed together and under what conditions and the computer output, with a high degree of certainty, what product will be. Until then, we’ll have to work with graphs and charts, albeit digital ones. 

After going through all the fruits and vegetables and whole food natural-type products, flavor companies found the research into new flavor compounds relatively unprofitable. This makes me sad. There was a forray into the flavorful world of common food reactions like fermentation and the Maillard reaction. By 2005, after cataloguing over 2,800 active compounds, the flavor and fragrance companies concluded they should perfect what they have before trying to find more tasty and smelly things. To my chagrin. There is the possibility that mixing and cooking ingredients together produces entirely unrecorded flavor and fragrance compounds but the vast majority of these combinations has not been researched. 

Marie Wright, flavorist, South Brunswick, New Jersey
Wall Street Journal "Creating Portraits"

To manage and master all the compounds we did find out about, the training of Flavorists came on the scene. This is an amazing job and what I want to be when I grow up. Here’s how the making of a flavor/fragrance compound goes: discovery of a compound in nature, perfection of synthetic imitation, painstaking purification, application of creativity to combine flavors in cool new ways, creation of a flavor profile (via an aromagraph), and playing around with the potential uses of the active compound. Upon his visit to Marie Wright's laboratory in New Jersey, Wall Street Journal Photographer Kyoko Hamada remarked: “I had been warned that Marie’s lab might be a bit like Willy Wonka’s Chocolate Factory. Upon entering the lab, we were overwhelmed with the smells of bubble gum, lemon, coffee beans, chocolate, tangerine, and what I’m guessing may have been cupcake, soap, vanilla, banana and amaretto, all mixed together in what was an otherwise very stark and minimal laboratory. It was strange to think that the smells which were so omnipresent in the air were completely invisible to the naked eye….Marie, the flavorist, was a self-assured, charismatic and very charming woman who didn’t dress at all like any scientist I had photographed before. It was great pleasure to meet her and such fun to visit the lab. I am grateful that she didn’t call the Oompa-Loompas when I ended up breaking one of their beakers in all the excitement.²”

Here’s a case study: a European blueberry (billberry) of interest due to its complex taste profile (in contrast to domesticated varieties) was found to contain 132 potential aroma compounds. A complete profile was created of all the aliphatic and aromatic structures, how ripeness affects the the flavor, and how growth location affected chemical composition. Extraction and purification was done using solid-phase micro-extraction (SPME) and analysis was done with GC-MS. Then, the compounds were assigned adjectives like “mint-spicy note” (1-8,cineole) or “flowery-fruity note” (acetate) or “herb-spicy note” (terpinolene). Collecting these results creates a sort of database for the fruit.³ A chemical map.

With enough information and structural alterations, the flavorist can say, “this smells basically like the kind of blueberry I want” as the sniff the mist that sprays out of the GC-MS. Say, a perfect billberry scent. “Now,” says the flavorist, “I’m going to go into the kitchen part of my lab and try it out in a blueberry muffin mix and then eat the muffins” And the processes is repeated until the desired flavor is acheived. 

The problem, as always, is that it’s not that simple. There’s quite the leap from knowing what a food is comprised of and getting those compounds into an applicable form, which is what the rest of the chapter details. 

Therefore, next time: the many, many technical difficulties of actually getting synthetic flavor compounds into food! (And how some very smart people figured out very cool things.) 

In the meantime, enjoy this video on Goldfish Cracker production. It's always fun (scary?) to learn about how our food is made - and to think about all the details they won't include. 

Ashley

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1 Ahmed, E., Dennison, R., Dougherty, R., Richard, H., Shaw, P. “Flavor and odor thresholds in water of selected orange juice components” J. Agr. Food Chem. 26(1) pp.187-91 ^↩


2  Horne, Rebecca. "Favorite 'Creating' Portraits" Wall Street Journal 2011. Accessed 14 Oct. 2014. http://blogs.wsj.com/photojournal/2011/07/18/favorite-creating-portraits/ ^↩

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3  Rohloff, J., Nestby, R., Nes, A., Martinuseen, I. “Volatile Profiles of European Blueberry: Few Major Players, But Complex Aroma Patterns” Latvian Journal of Agronomy. 2009. 12:98-103. ^↩

4 Rowe, David J (ed.) (2005) Chemistry and Technology of Flavors and Fragrances. Blackwell Publishing: Poole. Ch.9.^↩

Sensory compounds are, of course, not limited to cooling and tingling compounds. The breadth of tasteless, odorless chemicals that cause sensation is surprisingly wide and includes chemicals that cause feelings of warmth, pungency, heat, and astringency. Very few synthetic chemicals create the warming and heating sensations. Most of what I'm going to cover in this post comes from things like ginger, Szechuan pepper, chili pepper, mustard, horseradish, wasabi, cloves, and onions.


The first thing you're probably thinking is (maybe): well, warmth and heat are basically the same thing. This is not true in the complex world of sensory compounds. Warming compounds are generally considered to be more gentle (think: the comforting pleasure of vanilla) and heating compounds actually produce their sensation in the form of pain (think: one too many chili peppers). It does get a little confusing here since warm and hot compounds both typically contain "vanillyl moieties." Moiety was a new word for me, too, but it's a just another way to say that there's a structural component that resembles vanillin somewhere in the compound. It seems that the "warm" compounds tend to more closely resemble vanillin than the hot compounds. Most of these chemicals are also oleoresins - another great vocab word - meaning that they are oil-soluble extracts. This makes sense in context with many of the flavor and fragrance molecules being found in the essential oils of plants and naturally their sensory component isn't going to be too far away.

Vanillin
Wikimedia Commons

These warming and heating categories are really cool in all ways but the literal. I've heard a lot of arguments over the years about killing off your taste buds with spicy foods, or whether or not people in Thailand have genes that allow them to eat "Thai Spicy" curry, or if a food actually gets spicier the more of it you eat. Things like that. Science, as it often does, confidently answers these questions.

To answer a few urban unknowns:

Number 1. Desensitization at the nerve level does occur when eating spicy food, that is, something containing anything with a vanillyl moiety which can activate the VR1 or VRL-1 receptors in the mouth. These nerve channels will not activate as readily in a person who eats lots of spicy things compared to a person who does not. In short, no one's "killing their taste buds" with General Tso's Chicken, but they are acquiring something like an immunity to the sensation.

Number 2: This kind of blends into number 1, admittedly, but genetics does give one a sort of pre-determined threshold for spiciness. It's certainly not something that can't be overruled, however, by the above desensitization through regular exposure.

Number 3: Food doesn't technically get any "hotter" the more of it you eat, i.e. the chemicals I'm discussing here won't build on one another's presence. It might feel that the more chili you eat the hotter it gets as a result of repeated exposure to one of these sensory compounds (here, capsaicin) because the nerves simply haven't had time to recover from the prior exposure. Warming and heating compounds will cause the mouth to produce more saliva to "defend" itself against these irritating agents and help the nerves out but sometimes (I'm looking at you, wasabi) it's just not enough.

Hopefully that knowledge gives you a little insight into just how carefully crafted heating and warming compounds are in terms of their being additives in our food. Think about mild, medium, and hot salsas, for instance. Or muscle-warming lotions. Cosmetics are often considered more convincing and desirable from a consumer point of view if the user can feel the effects instantly, such as in products that enhance skin colors, like artificial tans. Maybe something about feeling a warming sensation causes the consumer to associate with lying on the beach? In any case, companies design use these compounds to enhance the flavors and smells of food, gum, mouthwash, lotion, liquor and more.

A kitchen staple? 

A current *hot* area of research, in fact, is finding synergies between these sensory compounds. What cooling, tingling, and warming compounds will enhance one another or create entirely new experiences for the consumer? Takasago International Corporation found that combining vanillin, a cooling agent, gingerone, and capsaicin created cool, warm and tingling effects all at the same time. This patent from von Borstel et al. on creating a better cigarette experience discusses throat feel, mouth sensation, and even reducing the nerve irritation caused by nicotine itself. Although I'm not sure what kind of product outside of cigarettes wouldn't overload one's mouth with all these nerve stimuli - gum, perhaps? - it's not an area of study that's likely to cool off anytime soon.


Ashley



1 Rowe, David J (ed.) (2005) Chemistry and Technology of Flavors and Fragrances. Blackwell Publishing: Poole. Ch.9.^↩

Very Cool Compounds

Just as there are molecules that make your tongue tingle, there's a class of compounds that create a cooling sensation. Why, you might ask, would major companies all over the world invest lots of time and money into creating chemicals that simply make your skin or tongue feel cold?

 First, there's a perception among consumers that coolness equates to freshness and cleanliness so the appeal of these characteristics in personal hygiene products like toothpaste, shampoo, shaving cream, etc. is high. Consumers want gum, medicines, breath fresheners, and more that cool without being bitter, burning, stinging or tingling.

Secondly, flavor and fragrance companies are seeking less expensive means of creating this popular refreshing sensation, so a number of both natural and synthetic molecules have come "on the market." The more "natural" a chemical is the better: it's appealing to consumers and often less complicated to make. Cheaper production of either, however, allows flavor and fragrance businesses to compete with each other for contracts to industrial producers.

Finally, research is being done to find out which cooling compounds work synergistically with other ingredients to enhance or alter products for desired traits. A number of new cooling compounds have been created as a result of this research that also work as stand-alone cooling agents.

There is a wide variety of cooling products.

The two most important traits of a cooling compound are duration and intensity. The best ratio of these traits varies depending on the product. A minty gum, for instance, might require a burst of flavor when initially bitten but maintain a refreshing feel as long as it's being chewed. A body spray, on the other hand, might be intended to make the skin feel slightly cleaner at the moment of contact (versus oily or dirty).

The many different uses of cooling compounds makes the chemistry tricky. The amount of menthol needed to make the gum seem to burst with flavor would likely go unnoticed on the skin because cells in the mouth, and thus nerves, are more nearly exposed. Likewise, the amount of a cooling agent used to make the skin feel fresh would probably be bitter and disgusting if used in a piece of gum.

In general, cooling compounds have a hydrogen bonding group, a compact hydrocarbon skeleton, both hydrophilic and hydrophobic structural components, and a molecular weight between 150 and 350g/mol. Certainly, the hydrogen bonding and lipophilicity are the two most crucial components of a cooling agent. The industry's favorites have h-bonding groups that are hydroxy, n-alkyl carboxamides (for rapid cooling), sulfides, and phosphine oxides.

Carboxamide Functional Group

The lipophilicity is crucial as many cooling components are added to the flavor or fragrance oil and mixed before other ingredients are added. Since many liquid products such as sodas or alcoholic beverages contain theses chemicals, it's important that the cooling agent is in an easily miscible vehicle to prevent separation.

Hydrogen Bonding in Water

There are many, many of these cooling compounds so I'll detail just a few to give you an idea of the chemistry behind their design and the desired properties that they fulfill. 

Menthol and its direct derivatives are among the most common and oldest cooling compounds because of their "natural" sources in peppermint and cornmint oils. Although the naturally derived menthol is subject to price fluctuation due to crop success, it's still usually cheaper than fully synthetic menthol. Interestingly, the L-enantionmers are up to 45X more active than their D-menthol counterparts and the cooling effects of L-menthol can be detected on the skin in a solution with less than a 1% concentration.  Even at as low as 2%, the effects of menthol become "anesthetic" or "irritating" and at greater than 0.3 micrograms, say, in a piece of gum, it is irritating to cells in the mouth.

L-menthol is a ~45x more active cooling agent. 

Flavor and fragrance companies take potent and common chemicals such as menthol and toy around with them, hoping to achieve something more marketable. Takasago, for example, used the highly purified menthol isomer L-(-)-Isopulegol to make a specialty ingredient that "provides freshness, crispness, and coolness to citrus fragrances."They renamed it "Coolant P," a practice common throughout the industry to simplify long and often structurally confusing IUPAC names. The author says of one popular carboxamide:

“When called by its chemical name the structure is confusing, indeed a rather more sane chemical name would be N-methyl 2-isopropyl-2,3-dimethyl propionamide. In any event, it is sold by some companies as WS-23…” (p.219). 

Sometimes chemicals will be developed for specific industry purposes, such as the completely synthetic L-Monomenthyl  succinate. First reported by the British American Tobacco Co. in 1962 for use in manufacturing tobacco, this cooling agent was reported again in 1965 as a flavoring agent in cigarettes. The tobacco industry found this chemical desirable and worth further research because it is easily synthesized by a reaction of menthol with succinic anhydride. Its addition to cigarettes makes them taste less disgusting, presumably, and is intended to leave the smoker's mouth feeling…clean? 

Other cooling compounds are designed without a specific product in mind, but rather for their appeal to consumers as an ingredient. L-(-)-Monomenthyl glutarate, a.k.a. “Cooler 2," is "nature identical" meaning that it's exactly the same as a natural product, just created in a lab. International Flavors and Fragrances markets this as just that - nature identical - because the designation funnily enough lies in slightly higher esteem than "synthetic." 

There are a few cooling compounds that I recall actually having seen on ingredients labels before: mannitol, sorbitol, urea, methyl salicylate and camphor. Though not related to menthol, these compounds all have a sweet cooling character. What's really cool is that in mannitol, urea and sorbitol this effect is achieved through heat of dissolution. So, it's not just your brain being tricked into thinking it feels cooler, but there's an actual heat exchange occurring over the surface of the cell. Pretty neat.

The final category is what I like to think of as experimental cooling compounds. These are things that aren't actually on the market because they're potentially not safe or not perfected. AG-3-5 or "Icilin" is one such compound. Although it's a very potent cooling agent that is reported to create a refreshing sensation from the mouth all the way to the stomach, it's also a suspected mutagen. No big deal.

In short, there are a lot of cooling compounds used for a variety of business and chemical reasons. So, next time you're chewing a piece of gum, try to mentally separate the cool, refreshing feeling from the flavor itself. It's a pretty cool exercise and something I hadn't thought about before. Plugging your nose while taking the initial chews also helps make this distinction - you'll notice that your mouth feels cool and clean without experiencing the mintiness to the same degree. And there are actually panels of scientists who decide which cooling compounds achieve this sensation most successfully! What a job.

Next time on the Taste of Chemistry: Warming Compounds!

Ashley

Speaking of stinky breath: Bonus Video!

 





1 Rowe, David J (ed.) (2005) Chemistry and Technology of Flavors and Fragrances. Blackwell Publishing: Poole. Ch.9.^↩