Coffee flavour is a very complicated mix of so many different elements: variety, roasting, grinding and brewing all play a unique part in making your perfect cup of coffee.
A lot of ink has been spent to describe all these factors, and we won’t be able to cover it all here. For those who are interested, you can read a bit more on coffee varieties, roasting and brewing here, here and here.
In this post, we’ll discuss how NIR analysis can be used to distinguish between different types of ground coffee. We’ll discuss a very rough classification of ground coffee, with no pretense to write a complete scientific investigation. Rough as they may be however, our results show that with little knowledge of the coffee samples one can be a fairly good classification that can have many uses. For instance it may provide a way to quickly detect adulteration, composition, degree of roasting and sensory perception of coffees. Sensory analysis is especially attractive: imagine if we could predict the taste of the coffee by measuring NIR spectra of beans or ground coffee blends. Even further, imagine if we could ‘design’ the desired coffee flavour starting from raw beans!
Well, that seems a big leap at the moment, so we set ourselves up for a simpler first step: basic classification ground coffee based on NIR spectra. For that we decided to use ground coffee of consistent quality (especially milling size) which has been already classified based on flavour strength. We chose Aldi Expressi coffee capsules, which comes in several varieties, each defined by an ‘intensity’ scale. Differences across the scale are due to different degree of roasting, and different coffee variety (Arabica and/or Robusta) as well as country of origin.
DISCLAIMER: Instruments & Data Tools did not receive any compensation, nor free samples from Aldi Australia or its parent company. We chose Aldi Expressi coffee capsules due to its large available selection and the possibility to compare NIR data to an external intensity scale. The data and comments provided here are not influenced by Aldi Australia in any way.
NIR analysis of ground coffee
We used NIR analysis to try and answer three simple questions:
1. Can we distinguish the content of different capsules from one another?
2. Can we separate coffees based on caffeine content?
3. Can we distinguish coffees based on chlorogenic acids content?
Question number 3 is especially interesting, as chlorogenic acid plays a role during roasting and influence the bitterness and the acidity of the coffee beverage.
OK, that’s the list of all capsule types we used, along with some information we gathered from Aldi website:
|La Spezia||11||Dark||Arabica + Robusta|
|Abruzzo||12||Dark||Arabica + Robusta|
|Calabrese||13||Dark||Arabica + Robusta|