What Do We Really Mean by a 'Strong Cup of Coffee'?

For this latest addition in our educational series, we thought it would be interesting to discuss the often-confused term ‘coffee strength’. Does a ‘stronger’ coffee contain more caffeine? Or does strength refer to the flavour intensity?

There is quite a lot of misleading, and even sometimes contradictory literature out there on this topic, and it is easy to see where confusion arises. In this blog we aim to alleviate some of this confusion.

 The Supermarket coffee strength scales. What do they really mean?

 Before moving on we thought we should first attempt to explain ‘strength guides’ that are often found on the front of supermarket coffee.

During a brief walk down the coffee isle in our local supermarket, we found strength levels from 1-4, 1-5, and 1-7. These scales are generally quite arbitrary, and at best perhaps give some indication of roast level but not much else.

 A coffee scoring 5/5 for strength will not necessarily be ‘stronger’ in flavour or contain more caffeine than another coffee scoring 3/5 but will likely be a darker roast.

Darker roasts do however generally contain harsher, more astringent flavours, which can give the impression that the coffee is indeed stronger. It is also important to note that roast profile alone has little impact on caffeine content.

 Brew Method:

We all have our favourite brew method, and this is actually an important point to consider when talking about coffee strength. It may come as no surprise that in terms of caffeine content the espresso comes out on top, but only ml for ml. A single 30ml shot will on average yield around 60-80mg of caffeine. However, a standard 235ml of filter or cafetiere coffee will contain more caffeine than a single espresso shot, around 96mg.

So, whilst the concentration of caffeine is higher in an average espresso compared to other brew methods, cup for cup a filter coffee could be considered stronger, since it contains more caffeine. Of course, these are rough guidelines, and the comparisons will be different depending on factors such as coffee to water ratios.

How then does brew method influence strength in terms of flavour?

For this we can refer to the amount of coffee that is dissolved in our cup (the technical term is total dissolved solids, or TDS, and is expressed as a %). Again, it may come as no surprise that the espresso contains the highest TDS%, averaging 8-12%, giving the espresso it’s characteristically intense flavour. An average filter coffee for comparison will be closer to 1-2%.

When coffee ‘strength’ is divided into two separate characteristics, caffeine content and TDS, the espresso will have the strongest flavour, but if you are looking for the strongest caffeine hit may contain less overall caffeine.

Coffee Strength By Varietal:

Something I wanted to find out was whether caffeine content varies from origin to origin. As I’m sure you’ve already discovered, coffee can vary hugely in flavour depending on where it sourced from. These flavour profiles are influenced by factors such as soil conditions, weather, and processing techniques. Caffeine however remains much the same… At least when comparing Arabica.

What I did discover was that Robusta coffee (Coffea Canephora), the cheaper, generally lower grade coffee, contains up to twice the amount of caffeine as Arabica (Coffea Arabica) around 2.2% and 1-5% respectfully.

This led me onto another interesting discovery. Caffeine is a natural pesticide of coffee shrubs. The odour wards off insects, and to pests that try and feed on the plant can cause paralysis. With increasing altitude, the threat from pests becomes less. Robusta is generally grown at lower altitudes (c.760m) than Arabica (1000m+) and this explains why the caffeine content is higher.

 In Summary:

Coffee strength can refer to both the intensity of flavour, which is dictated by the concentration of dissolved coffee in the cup, and overall caffeine content. Both characteristics are influenced by brew method, cup size.

Supermarket coffee strength guides are at best an indication of the roast level, but the scales are often quite arbitrary.



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