Scitech | Coffee chemicals

A cup o’ joe sounds more like an organic chemistry lab than a beloved drink

Legend has it that coffee was first concocted in Western Ethiopia. Since then, it has come a long way. Modern brewing devices and techniques have conferred a mechanical advantage upon coffee-making that has turned the process into both a science and an art. At the same time, popular coffee derivatives – like the frappucinos served at Starbucks – contain a slew of additives that make the drinks seem more like frosted cocktails than cups of coffee. Whether your morning kick involves one of these or a genuine barista-brewed artifact, the lowest common denominators for all coffee, and the entirety of its offspring, are simply water and coffee beans.

The most popular and accessible species of coffee beans on the market are Coffea robusta, a bean associated with a harsh, flat taste, and Coffea arabica, which is known to have a richer and multi-dimensional taste. 70 per cent of the world consumes Arabica, while the remaining 30 per cent drinks Robusta. They have slightly different chemical compositions, but both contribute a total of over 1000 different organic and inorganic chemical compounds to this drink. These include carbohydrates, lipids, nitrogenous compounds, vitamins, minerals, alkaloids, and phenolic compounds. Of this teaming multitude, polysaccharides, phenolics, and caffeine have the most salient impact on health.

Caffeine, the cardinal reason many students drink coffee, is a white crystalline alkaline plant toxin, similar to nicotine and cocaine. Its main function is to prevent adenosine from bonding to neurotransmitters. Adenosine, also known as the sleep chemical, is an inhibitor that abates brain activity by restraining the reticular activating system. In other words, it makes you sleepy. The presence of caffeine prevents this system from being inhibited, thus allowing you to power through those early mornings and late nights. In broader terms, caffeine is a central nervous system stimulant. It can make you more alert, but can also cause insomnia, headaches, anxiety, and dizziness. Caffeine is also a diuretic – a urine-inducing compound.

Caffeine’s potency is especially remarkable when paired with the fact that a cup of coffee is typically composed of 98.5 to 99 per cent water. This may seem like you’re being royally swindled, but the universal solvent is important in the brewing process: it extracts the flavors and oils from the coffee grounds, lending your morning dose its pungent nature. With less water, the 800 or so volatile aromatic compounds that harmonize to produce the distinct smell and taste of coffee would be overwhelmingly cloying and unsavory.
A select group of these volatile compounds have a low odor threshold, are found in high concentrations in coffee, and end up forming the primary determinants of coffee’s aroma. Ethylguaiacol, for example, is the flavor constituent that lends certain blends a spicy fragrance. Pyrazine – the main aromatic compound in green bell peppers – provides an earthy aroma. Diacetyl is responsible for a buttery smell, and furaneol is the éminence grise behind the caramel-like flavor of many coffees.

Besides having pleasing olfactory characteristics, coffee contains other compounds that are thought to have salubrious side-effects. Coffee beans are rich in indigestible polysaccharides, dietary fibers that are associated with antioxidant phenolics. A report published in 2007 in the Journal of Agricultural Food Chemistry found that these antioxidant properties are passed on after brewing. With 8.7 to 10.5 milligrams of antioxidant phenolics per 100 millilitres of the brewed beverage, coffee has more soluble fiber than many other common beverages. Type II arabinogalactan and galactomannan are the polysaccharides that are present in both the green coffee beans and the final product. Green and roasted coffee beans are rich in dietary fiber, and since phenolics have a tendency to bind strongly to polysaccharides, they are transferred to the brewed coffee. The correlation between regular coffee consumption and lower risks of diabetes may be explained by the presence of antioxidants in coffee. However, the fact that coffee is the number one source of antioxidants in the western drinks shouldn’t be interpreted as a justification for increased coffee consumption, especially given its less beneficial aspects.

One of these is that coffee has been linked to higher levels of cholesterol. This may seem discrepant with its soluble fiber properties, but coffee’s potential health benefits may be jeopardized by some of the extra components that are added to the coffees many people opt for these days. For example, Starbucks coffees are closer to glamorized full-fat milkshakes, with a higher calorie and carbohydrate load than regular coffee has.

Frappuccinos, for instance, are made with different variants of syrup whose main ingredients are sugar, water, xanthan gum, sodium, and preservatives. Xanthan gum is a polysaccharide that acts as a thickening agent. Depending on the drink, many of the syrups contain maltodextrin, a sweet additive usually added to sodas and candy, and carrageenan, the vegan version of gelatin that is extracted from red seaweed.

The composition of a type of beverage isn’t static – chemical processes determine the exact chemical makeup of a cup of coffee and have a qualitative and quantitative effect on your quotidian beverage. For example, according to the Journal of Agricultural Food Chemistry, a dark roast produces more N-methylpyridinium, a chemical compound that prevents stomach cells from producing excess acid usually caused by coffee drinking. The darker the roast, the more soothing the coffee will be for the consumer’s stomach.

The extraction process also impacts the final components in a cup of coffee. Acids are the first components to be dissolved in water. Sugar comes next, and the bitter coffee components are dissolved last. Too much extraction can produce a bitter flavor, but too little will result in a sour brew. The magical number, according to Richie Nieto, the owner of a coffee bar in New York, is a 19 to 22 per cent extraction, a formula that pleasantly balances all three types of compounds.

No matter what the magical blend is, a cup of coffee ultimately boils down to a cup of water sprinkled with some caffeine, ethylguaiacol, phenolics, diacetyl, amongst many others. So romantic, I know.


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