Hmmmm... 2-furylmethanethiol, guaiacol, 3-mercapto-3-methylbutylformate, (E)--damascenone ... the smells of a good, rich cup of coffee. The molecules that give rise to that distinctive odour that for millions of people signals the start of a brand new day.
The aroma of coffee is a complex mixture of over 800 different chemicals. Or, at least, over 800 different chemicals that we have identified. More will be uncovered as analytical techniques improve.
It is important to realize that all of these chemicals are "naturally" occurring. They are a natural consequence of roasting and brewing coffee. Just because they have unpronounceable names doesn't mean that they are bad, harmful, or synthetic.
There are a number of television commercials for a variety of products that essentially have a tag line that says: "It must be safe for you because you can pronounce the name." Arsenic is a name that pretty much anybody can pronounce and yet it is incredibly poisonous. Being able to pronounce a name doesn't make it safe.
More to the point, not being able to pronounce a chemical's name doesn't make it bad. Most of the chemicals found in the aroma and taste of a cup of coffee have tongue-twisting names such as those above.
Others aren't so bad - such as vanillin which is the component that adds a hint of vanilla flavor to every cup of coffee. Vanillin, interestingly enough, is one of our comfort molecules and even though it occurs naturally in roasted coffee beans, some blends increase the level to give a more desirable blend.
In any case, it is a combination of all of the molecules plus the oils, salts, and other compounds that gives coffee its complex and distinctive flavour. Judging by the lineups I see at Tim Hortons every morning, it is an essential part of many people's everyday ritual.
It is not just the aroma, of course, that people are after. It is that jolt of caffeine that helps to sustain us when we are tired and wake us up are a night's sleep. Caffeine is another naturally occurring chemical and some would argue one of more essential components of coffee.
It is because coffee is such a rich blend of chemical components that brewing a good cup or finding a blend with just the right flavour is so difficult. Indeed, brewing good coffee is much more of an art than a science.
But there is still science involved.
For example, clean, pure water makes a big difference to the taste. Organic molecules, such as those generated during brewing, can be rich in functional groups that bind to metal ions thereby changing their physical properties. Minerals in water can bind to molecules in coffee rendering them tasteless at best and disgusting at worst.
There is also little doubt that different growing regions produce coffee beans with distinctive flavours. Kona coffee from Hawaii tastes different from Jamacian Blue Mountain. And for really unique, there is the ultra-expensive Kopi Luak where the bean has been pre-digested by a small cat-like animal.
There is even a variation of coffee where the beans are harvest from elephant dung.
But a really good cup of coffee depends not just on how a bean is grown or harvested but also on the roasting process. Under-roasted coffee doesn't have a full rich flavour. Over-roasted tastes burnt.
Much effort has gone into researching how to perfectly roast a bean.
That's not all the science in a cup of coffee. It's a wonderful place to watch convection in action. I can remember as a kid being fascinated with the plume of light brown that swirled out of the depths of a coffee cup upon the addition of milk. What I failed to notice at the time is that the surface of coffee provides evidence of the inner turmoil within a cup.
When a liquid gets hot, it expands. It is a very slight expansion, but it an expansion nonetheless. The result is that the hot liquid becomes less dense relative to the same liquid cold.
Coffee cools from the surface down. Heat is lost from the surface to the surrounding air. This results in a temperature inversion with the colder liquid on top. Being colder, it contracts a little and becomes more dense than the liquid below.
This is an unstable situation but in order to trade places the hot less dense liquid at the bottom of the cup (which is well insulated) must rise past the cold liquid on top. It does this by forming convection cells. In an unstirred cup of black coffee, these cells appear as hexagonal patches surrounded by dark lines.
And that, if you will forgive the pun, is only skimming the surface of all of the different science that can be found in a cup of coffee.
