Coffee: serving up chemistry in every cup

Origins of our favorite brew

The word «coffee» was introduced in 1582, derived from the Dutch «koffie». This traces back even further to the Arabic word for coffee, «qahwah», which has been speculated to come from «quwwa» (defined as power or energy), or even from Kaffa (also spelled as Kefa) which was a medieval Ethiopian kingdom that exported coffee plants to Arabia. It is believed that coffee was first discovered by a goat herder in Ethiopia who noticed the energy of his goats increase after consuming the coffee fruit (known as «cherries»). From Ethiopia, coffee consumption spread through the Arabian Peninsula and Middle East during the 15th and 16th centuries.

Good coffee: not as straightforward as you might think

Coffee comes in many forms, with niche roasters looking to discover new flavors daily. Since the gourmet coffee market is growing more, specialty coffee is also in high demand. Global Brands Magazine reported the price of Black Ivory Coffee at $500 per pound ($1,100 per kg) in 2020.

Why so expensive — is the taste that good? In order to make Black Ivory Coffee, the coffee cherries are fed to and digested by elephants. The resulting coffee beans are then cleaned, dried, and roasted. Black Ivory Coffee is produced in a similar manner to Kopi Luwak (or civet coffee), another expensive type created by the fermentation of coffee cherries in the gut of civet cats.

Typically, coffee is grown in (sub)tropical areas, but the ideal climate differs depending on the species. Some prefer higher altitudes and are more suitable for mountainous regions. Others need hot and dry conditions to produce the best quality beans. Now there are over 70 countries that produce coffee. That’s a good thing, because global coffee consumption in 2020/2021 is estimated to be 167.23 million 60 kg bags, which is more than 10 million tons of coffee!

Changes in coffee consumption practices

The adoption of the pod coffee machine (e.g., Keurig, Nespresso) over the past decade has pushed the consumption of coffee from something generally enjoyed in a café, restaurant, or on the go, to a much higher rate of consumption at home. With this significant shift to pod coffee, the ability to adjust grind size, water temperature, or extraction time used by the best baristas to counter changes in flavor and strength is no longer a possibility. In fact, the ease of pressing a single button and receiving hot, fresh coffee within seconds is exactly why pod coffee is so popular. This puts new pressures on coffee roasters to maintain the flavor and caffeine strength expected of their brand and varieties.

Science—brewing up your perfect cup

Not all coffee beans are created equal, but luckily science allows us to define many of the key quality parameters that result in the taste and caffeine strength we expect from our favorite brand of coffee. Coffee is generally acidic with a pH of around five. Highly acidic coffee displays a sour, harsh flavor. While there are ways to counteract this on the consumer side, for manufacturers it is even more important to identify that there is an issue to begin with. A simple identifier is the titratable acidity of the coffee, and this has a direct correlation with the taste you associate with your favorite brew.

The pH and acidity of coffee samples are analyzed using a robust pH electrode during titration against standardized sodium hydroxide. Caffeine is determined through a redox back titration after a known excess of iodine is added to the sample and left to react. After the reaction period, the sample is filtered and titrated with sodium thiosulfate.

Near-infrared spectroscopy (NIRS) can also be used to measure various quality parameters in raw (green) coffee beans as well as in the final roasted product. NIRS is fast, simple to use, and requires no chemical reagents, however it must be used with a primary method (such as titration). NIR spectroscopy can determine density, moisture content, water activity, as well as caffeine content in coffee.

Hopefully this article has given you some insight into coffee’s long journey from the farm to your cup, and that you have learned about the chemistry behind the way your coffee tastes! Enjoy International Coffee Day, whether you celebrate on October 1st or every other day of the year.

Your knowledge take-aways

Application Note: Analysis of caffeine, pH, and acidity in coffee – Fully automated determination including filtering, reagent addition, and sample pipetting using OMNIS

Application Note: Analysis of green coffee beans by near-infrared spectroscopy – Reliable density, water activity, and moisture results in seconds

Application Note: Roasted and ground coffee analysis by near-infrared spectroscopy – Fast determination of caffeine, water activity, and moisture