Coffee Chemistry

Like many others out there, I require at least one cup of coffee a day to function – in fact I am drinking a cappuccino as I type this. Interestingly, there is more chemistry involved in the brewing and consumption of coffee than just getting your caffeine fix. We also explore death by coffee, because that’s what the masses want. Right?

There are many aspects of coffee chemistry we can discuss, from the roasting process to the classic ‘how much caffeine will kill you’ question. We’ll touch on these here as I enjoy this cup of coffee and see how many more cups it’ll take for me to finish this article.

Let’s begin. Coffee beans are actually not beans, but the seed of the coffee fruit (surprise!) which are then processed, cleaned and dried to produce green beans. Unfortunately these green coffee beans contain a whole host of volatile compounds which are released upon steeping (soaking in hot water) and hence they are roasted in the next stage of the process.

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Roasting

During roasting, the major part of the unpleasant-tasting volatile compounds are neutralised. What this also does is release the characteristic colour and aroma of freshly roasted coffee beans by the creation of Maillard reaction products (MRPs) – remember them from the final process of baking? MRPs – though not well known – include menaloidins which have antioxidant properties.

The higher the temperature at which coffee beans are roasted, the oilier and darker in colour they get. This is due to oxidation reactions occurring within the chemicals inside the bean, which are slowly expelled and broken down.

roasting

Caffeine is a rather stable molecule owing to its aromaticity (ten π electrons within its 5,6 ring core). It can be extracted by passing soaked coffee beans through activated charcoal – this ‘caffeine extract’ can then be used in energy drinks and caffeine tablets while the beans sold as ‘decaffeinated’… a waste of good beans, if you ask me.

Chemical Stability

As mentioned earlier, caffeine being stable means it is difficult to break down as the bean is roasted. This results in very dark beans having only slightly less caffeine content than the starting unroasted bean. The majority of other chemicals – that give the aroma and taste characteristic of the bean – are broken down much quicker, that’s why very dark beans lose their coffee-ish taste and taste more like roasted carbon.

Lethal Dose of Caffeine

Okay, we’ll finally get to the part all of you have been waiting for – how much caffeine will kill you? Caffeine enters the bloodstream quickly and is an antagonist of the adenosine receptor in the brain, causes constriction of blood vessels and increasing blood pressure by blocking the effects of adenosine (vasodilation)2. It is metabolized via the cytochrome P450 1A2 pathway in the liver into 3 metabolites, each with further physiological effects.

Caffeine_metabolites

The lethal dose of caffeine is 3 to 10 grams in a short period of time3 – depending on an individual’s age, gender, metabolism, etc. – which equates to drinking around 30 shots of single espresso (~100 mg caffeine) in one sitting. Ventricular arrhythmia, in which the heart no longer contracts properly, the tissues no longer receive blood, and the patient dies, is the most common cause of caffeine-related sudden death.

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Death by coffee? (Source)

Alright, I’m out of coffee. Time to get more.

Reference:

  1. Illy, A., & Viani, R. (2005). Espresso coffee: the science of quality. Academic Press.
  2. Daniels, J. W., Molé, P. A., Shaffrath, J. D., & Stebbins, C. L. (1998). Effects of caffeine on blood pressure, heart rate, and forearm blood flow during dynamic leg exercise. Journal of Applied Physiology, 85(1), 154-159.
  3. Sepkowitz, K. A. (2013). Energy drinks and caffeine-related adverse effects. Jama, 309(3), 243-244.