Why Does Coffee Taste Bitter?

Answers to this can be very simple or very complex so, as most of us are not chemistry experts, we'll keep it straight forward. There are very many variables so we will assume you are going to a decent coffee shop or buying good quality beans to brew at home. 

Coffee beans contain around 1,000 different compounds, many of which are water soluble i.e. they will dissolve in hot water. The most readily soluble tend to taste sour, the next have delicious flavours like caramel, nuts and chocolate whilst the least soluble mostly taste bitter.

The flavours most of us are after are the caramel, nutty and chocolatey (from the middle group), with a bit of acidity to lift and brighten the flavour (from the first group).

Luckily for us, we can achieve this simply by thinking about how we extract these compounds when we're brewing. This means, mainly, correct grind size and correct timing - both of which vary depending on how we are brewing.

In essence, each tiny bit of coffee we use needs to be the right size. This is known as the 'grind size'. The finer the grind size (such as when brewing espresso) the larger the total surface area is exposed to the hot water. This means the water can access the compounds quickly so a shorter extraction/brewing time is needed - in the region of 25 to 30 seconds. With a coarser grind (such as brewing in a cafetière) there is a smaller total surface area so a longer extraction/brewing time is needed to extract the flavours - in the region of 4 to 4½ minutes. 

All that said, we must time the extraction so that when the first two groups of compounds have been extracted we stop extracting. If the extraction is continued past this point we start extracting the bitter compounds - which causes your coffee to taste bitter.

Remember: you can specify the correct grind to suit your brewing method on every one of our product pages - it's free.