Everyday millions of people around the world begin their day religiously with a morning cup of coffee. Though today we easily identify coffee in its beverage form, it wasn’t always this way in the beginning. Throughout history, coffee has taken on several physical transformations, initially serving as an energy source when nomadic tribes combined coffee berries with animal fat as an early form of an energy bar. Later it was consumed as a tea, then a wine, and finally to the beverage we’ve come to identify today. Since the beginning, coffee has always been a product of great mystery, having been discovered accidentally in wild forests of Abyssinia (Ethiopia) and consumed in its native cherry form, then later, passed through fire to significantly alter its chemical state. And although coffee has been in existence for thousands of years, its only been in the past half century or so, that scientists have been able to truly identify and understand what exactly is contained in this mystical bean. To date scientist have identified over 1,000 compounds in coffee, which when compared to products such as wine of chocolate that are composed of a few hundred, pale in comparison to that of coffee. Luckily through advancements in technology, much of coffee’s chemical make-up has been unlocked and we now have a better perspective on the chemistry contained within this mystical bean.
For many, coffee drinking is simply a delivery medium for a potent alkaloid we have come to identify as caffeine or technically as 1,3,7 – trimethylxanthine. Although caffeine is strongly associated with coffee, its production within the plant kingdom is not exclusive but is seen throughout several other forms of plant life. Mate, for example, which is traditionally consumed in parts of Uruguay and Argentina, contains less than one percent by weight. Whereas, tea leafs (Camellia sinesis) which originated in China, contain almost three times the concentration of caffeine than Arabica, with Brazilian mate almost twice that of robusta coffee. Turns out that Mother Nature was quite generous when it came to distributing caffeine amongst the plant kingdom.
But for humans, caffeine is very unique. Thus far we are the only living forms on Earth that readily seek caffeine for both its stimulatory and psychological effects. For all other life forms, caffeine is a potent toxin capable of sterilization, phytotoxicity and antifungal properties. As such scientists believe that caffeine, with its intensely bitter taste, has evolved as a primitive defense mechanism in coffee ensuring its survival in the wild for thousands of years. It’s no suprise then, that the caffeine content of the more “robust” Robusta species is almost double that of the more delicate Arabica. The belief is that as insects attack the coffee cherry, they are deterred by the bitter taste of caffeine and simply move on to the next crop. Since Arabica is typically grown at higher altitudes than Robusta, where the attack of insects is reduced, Arabica has evolved to produce less caffeine.
With caffeine playing such an important role in the plants survival, one may also expect it to play an equal level importance during coffee roasting. Turns out, the fate of this imperative compound is far from spectacular. Although caffeine has a boiling point (sublimation) of 178oC (352oF), model studies has shown that caffeine readily survives the roasting process even at temperature far exceeding 204oC (400oF). Though the reasons for this remain unclear, but it is believed that caffeine’s strong complex with other compounds within coffee matrix create a strong retention that prevent it from further sublimation.
One common misconception in coffee, is the belief that darker roasted coffee contains a higher level of caffeine than lighter roasted coffee. This common belief makes perfect sense and stems from the fact that as coffee is roasted darker, it also increases in both astringency and bitterness. Since caffeine is also bitter, the correlation makes perfect sense, though careful inspection would show otherwise. Lets take a closer look:
Lets say we have 100 grams of green Arabica coffee, we can estimate its caffeine content to be roughly 1.2% on a dry basis (1.2g caffeine / 100g coffee x 100). Now, lets assume that we roast this coffee to a light roast and lose 10% by weight in the process. At this point, we no longer have 100g but rather 90g of coffee. Since the caffeine content within each bean has remained the same, our total caffeine content is now 1.33% (1.2g caffeine / 90g coffee x 100). So in reality, although the caffeine content stays the same per bean, from a weight perspective we observe a slight increase. The case for which roast has more caffeine is more a matter of perspective, than science.
Another less known alkaloid that shadows in the light of caffeine is that of trigonelline. In Arabica coffee, trigonelline concentrations make up roughly 1% by weight with a slightly less concentration (0.7%) found its Robusta counterpart. Although its concentration is slightly less than that of caffeine, it plays a significant role in the development of important flavor compounds during roasting. But unlike that of caffeine, which survives the roasting process, trigonelline readily decomposes as temperatures approach 160oC (320oF). Model studies have shown that at 160oC, sixty percent of the initial trigonelline is decomposed, leading for the formation of carbon dioxide, water and the development of a large class of aromatic compounds called pyridines. These heterocyclic compounds play an important role in flavor and are responsible for producing the sweet/caramel/earthy- like aromas commonly found in coffee.
Another important byproduct produced during the decomposition of trigonelline is nicotinic acid, or vitamin B3 – more commonly known as niacin. Depending on roasting conditions niacin can increase up to ten times its initial concentration, providing anywhere between 1mg of niacin per cup for Americano type coffees and roughly two to three times this concentration in espresso type beverages. When one considers that most people in the United States consume on average 3.2 cups of coffee per day, according to the National Coffee Association (2008) – makes coffee an ample source of dietary niacin. So far that great news for people suffering from an unbalanced diet, but there is another therapeutic benefit to coffee that is even more suprizing. Recently, Italian scientists discovered that drinking coffee may lower our incidence of dental caries. According to researchers, trigonelline prevents the adhesion of mucus-like byproducts onto teeth enamel (created during fermentation) that eventually leads to teeth damage. In the end, it looks like drinking a cup of coffee may not only keeps the doctor away, but also the dentist.
Lipid production and its subsequent survival after the roasting process play an important role to overall coffee quality. In general, most of the lipids exist in the form of a coffee oil and are located within the endosperm (bean) of the cherry, with only a small percentage deposited onto the outer portion of the coffee wax. Coincidentally, scientists have analyzed and discovered that much of the chemical make-up of coffee oil is very similar to that of vegetable cooking oils. As such, much of the lipid content in coffee remain unchanged and relatively stable even at the elevated temperatures associated with roasting. In its green form both Arabica and Robusta coffee contain on average 15-17% and 10-11.5%, respectively. But because Arabica contains about 60% more lipids than Robusta, many believe this stark difference is one reason responsible for quality difference between both species. Thus far, the claim has remained unconfirmed, until French scientists recently discovered a direct correlation between lipid content and overall cup quality. It turns out that as lipid content increases within the bean, so does overall cup quality. It’s a very plausible explanation when one considers that the majority of important flavor compounds in coffee are also fat soluble.
So did you ever wonder how complex coffee can be? With over 1,000 compounds coffee is more than just caffeine. In part II of this series we will discuss the role of carbohydrates, proteins and a number of aromatic compounds give coffee’s its alluring flavor.