Have you ever taken a sip of coffee and tasted flavours such as lemons, chocolates or even stone fruits and ever wonder why it tastes like it does? I have had a fascination with coffee from the first time I tasted ‘real’ coffee and it has always left me wanting to know more about the chemistry composition of coffee itself. In this blog, I will be talking about why I love coffee chemistry as well as my ideas behind it.

What interests me about coffee chemistry?

This is a topic that I have a huge passion for. We all love coffee and appreciate its unique characteristics but we often skip the inside activity that happens during the extraction process. When I taste a coffee, let’s say a Kenyan for arguments sake, I may taste berry like notes, jammy mouthfeel with a hint of vanilla, but in my mind, I want to know why the coffee tastes like that. I know that certain criteria such as altitude, soil conditions as well as variety and processing methods can play a huge role in terms of flavour profile but what makes up those flavour compounds? Was it possibly the roaster that carefully monitored the rate of rise in temperature or created that perfect roast profile or could it be that a particular bean has a composition of certain acids, let’s say citric and malic acid, and that possibly brings out some sort of enzymatic flavour compounds such as pineapple!? These kinds of questions really excite me and then I think to myself, how can I highlight certain notes when brewing this coffee.

For me there are 5 key parameters to brewing a coffee. Here they are:

  • Quality water: Water is often overlooked but it is essentially the main ingredient. In a good brew water consists of just over 98% of the total brew so it is vital that we get our hands on premium quality water so that we have no offensive flavours.
  • Water temperature – This is a sector that many people guess and it is essential that we use a fixed value to achieve consistency. When brewing, it is best to stick to 92 – 96 degrees Celsius to achieve the best results. I always use the ‘washing dishes’ analogy when referring to water temperature. Imagine yourself standing at the sink about to wash a greasy plate that you just ate your dinner off. As you turn on the hot water it will start to clean the plate, but as the water temperature increases this will start to strip away the grease faster and faster. We can say that the hotter the water, the more effective it is in extracting compounds from our ground coffee. It is always good to play around with the temperature to see what works best with the coffee that you are using.
  • Coffee to water ratio – How much coffee / how much water? When it comes to manual brewing I hear all sorts of recipes that people tell me. Per SCA, they recommend 60g of coffee per litre of water. Personally, I find this to work 99% of the time for me. It gives the final brew that perfect balance of strength and extraction.
  • Grind size – When it comes to grind size I always use the analogy of a cube of sugar and granulated sugar. If you place these two examples into a cup of hot water you will see that the cube of sugar will dissolve at a slower rate due to its size. Now when it comes to coffee the same principle applies, a larger grind size will dissolve slower than a fine grind such as espresso. It is always good to match the grind size to the brewing device that you are using and keep the logical principles in mind.
  • Time of extraction – This is a very important parameter that needs to be monitored to achieve the perfect cup. I always refer to a cup of tea when talking about time of extraction. Leave the tea back in too long and it will result in an over extracted cup with a dry astringent aftertaste, adversely leave the bag in for too short and the cup will be very weak, watery with a quick finish. The brewing time in critical as this is the point where acids, sugars and oils escape the bean fibres into the final brew.

Coffee is a science and every step plays a huge role in the final brew. When we look at water there are so many minerals, but what minerals are important and how much of what do we need? The list goes on and therefore I find coffee so fascinating; personally I could never become bored of such a complex ingredient that has endless avenues.

What aspects of chemistry determine the ultimate cup?

When looking at a cup of coffee I personally look for two determined factors, these are strength and extractions. Now when brewing coffee, whether it is an espresso or manual brew such as V60, the chemistry remains. We need to follow a recipe to determine the final brew but also to ensure that we can deliver that same product time and again! When it comes to the ultimate cup I think there are two ingredients that need to be of superior quality, these are water and coffee. I personally find that R.O (Reverse Osmosis) water is far superior than tap or filtered water and controlling the total mineral content is very important in the extraction process of brewing. Minerals assist in pulling out flavour compounds in the bean fibre and too high or too low mineral content will affect the overall brew. Bean quality is really important as well as how the bean was roasted. A badly roasted bean will result in a bad brew. Roasting is a science alone and hundreds of chemical reactions take place during the roasting process.

At the end of the day I believe that as a barista or coffee lover we understand that there is a whole bunch of chemistry going on in our brew and we may not fully understand it but following certain parameters will make our coffee a whole lot better and hopefully help us understand the chemistry side of things. I personally consider all aspects of brewing, this can be anything from water, PH level of the coffee during extraction, strength and extraction levels as well as charting my brew using the coffee brewing control chart. The coffee brewing control chart was designed by Dr. Earl E. Lockhart who was the first director for the Coffee Brewing Institute (CBI), which was formed in 1952. This chart helps you visually understand what the final product will taste like as well as guide you into the right direction to achieve certain levels of strength and extraction. It does take some time to understand how to adjust each axis but once you understand it then it helps you brew at a much higher level.

Why Coffee Chemistry?

I come across so many coffee enthusiasts on a daily basis, all passionate and love coffee but where I see the gap between them and myself would be the chemistry side. When I make a cup of coffee I visualise every aspect, I calculate each step to ensure that all parameters fall into place and create a final product that is not just a hot drink called coffee but a sensory explosion that can change the whole experience altogether. As a barista, we are the final key in the production line and there is a huge amount of pressure on us. I feel that as baristas we should strive to learn more about this amazing ingredient that we use on a daily basis, look deeper into what makes our coffee taste better and what elements we can control to improve the final experience.