Varieties, origin, flavour note. These are all factors that are commonly associated with contributing to the flavour of the coffee. However, while being overlooked, the temperature of the water (as used in the brewing process) dictates the process known as ‘extraction’. Here’s how extraction works.
Water is imperative for any coffee brewing process, as water is required to extract the flavour from the coffee grounds. As you may have guessed, this process is called ‘extraction’. At a molecular level, roasted coffee contains over 1000 chemical compounds. These chemical compounds include aroma compounds (also known as ‘solubles’) such as Methylpropanal (which provides a floral and spicy aroma) and Furaneol (which provides a sweet and caramel aroma); all of which contribute to the differing tastes and aromas of a brewed cup of coffee.
Now comes the temperature. Simply put, the temperature determines how quick the extraction takes. For an ideal extraction, the temperature of the water should be between 90 to 95 degrees celsius. If the water is too hot, the flavours will be released too quickly, resulting in a bitter and unpleasant taste (a result known as ‘over-extraction’). By contrast, if the water is too cold, it can take between 12 to 20 hours for the flavours to be extracted (this process is also known as ‘cold brewing’). However, if coffee is being brewed to be served within a shorter time, low-temperature water can result in an under-extracted coffee with a flat and sour taste.
Not only does temperature contribute to the speed of the extraction. It also highlights the various flavours in different ways. This is because the different coffee solubles dissolve at different temperatures. In other words, less acidic flavour compounds are more likely to be extracted by water with a low temperature, whereas a higher temperature will draw out a much more full-bodied flavour profile from the coffee.
So as you drink your next hot cup of coffee, you may notice something strange happening: as the temperature of the coffee drops, the flavours and aromas slightly change. This has much less to do with your olfactory system than it does with the dynamic chemistry that is taking place within the compounds of the coffee itself.