What makes a coffee strong?

strong coffee

Mocopan Coffee’s Babin Gurung on what coffee strength means and how to achieve it. 

During my barista hustling days, customers often told me they liked their coffee strong. I had no problem adjusting to customers’ needs, but found many people had different ideas of what “strong” meant. Some of the things strength commonly referred to was more caffeine, darker roast, or sometimes, just bitter coffee. These ideas aren’t necessarily wrong, but here in the coffee world, when we say “strong”, we mean the strength of flavours contained in an espresso. 

Babin Gurung
Babin Gurung is the New South Wales Barista Trainer of Suntory Coffee Australia.

Bitterness in coffee can result from a number of other things, like roasting profile, staleness, over-extraction, or not cleaning the machine properly – none of which make your coffee stronger.

More caffeine does not always mean a better coffee. Robusta coffee has a higher caffeine content than Arabica and some coffee brands prefer it because of that. But for an espresso coffee, at Mocopan, we generally stay away from Robusta due to its harsh flavour. 

Still, it’s not only the coffee you use that determines caffeine content. An ongoing industry debate is the effect of roasting on caffeine. Some believe darker roasts lead to higher levels, while others argue the opposite. Various studies have measured the amount of caffeine produced through various roasting profiles, but due to a large number of variables, such as coffee variety, density, and the molecular structure of the beans, it has proved a difficult task. In most cases, caffeine levels were consistent throughout the roasting process.

So, the most common and consistent method baristas use to make coffee strong is by adding extra shots of espresso to a drink. This means you are getting a higher coffee-to-milk ratio in the cup, making it taste stronger. 

However, if you are looking to increase strength in a single shot, you will need to adjust the brew ratio. This refers to the ratio of ground coffee to water. Smaller ratios produce more concentrated, strong coffee, while a larger ratio results in weaker coffee. 

There are three main ratios that apply to most espresso-based coffees:

  • Ristretto (1:1) – This has a ratio of one gram of coffee to one gram of liquid, which results in a stronger shot, and produces intense flavour with big body. A ristretto mostly captures heavier flavours but is known for lacking clarity of others. 
  • Espresso (1:2) – This is the most common ratio applied by baristas. Compared to a ristretto, an espresso has more water flowing through the same amount of coffee, which extracts more flavours, giving it a well-rounded taste. Along with body, you get more clarity of flavours.
  • Lungo (1:3) – This style of coffee is not very common. The coffee is more diluted in this ratio, which can result high extraction of flavours but decrease in intensity. Coffees with delicate flavour notes could benefit from a lungo ratio.
strong coffee
Figure 1: An example of how the composition of coffee affects flavour.

These brew ratios reveal that a stronger coffee is not always more flavoursome. If you want to achieve a higher extraction of flavours, you need to also understand the role of dose and extraction time. 

A coffee bean is a complex mix of soluble compounds that give coffee its colour, flavour, and aroma, along with caffeine. The flavour of coffee depends highly on its origin, variety, processing, and roasting profile, but generally speaking, it will have a combination of acidic, fruity, sweet, nutty, vanilla, and chocolate flavours along with dark and bitter flavour notes (see figure 1). 

It’s important to understand that different solubles dissolve at different extraction rates. Therefore, by controlling the amount of time the coffee is exposed to water, you can control what flavours you absorb from that coffee. 

Each coffee has its own unique properties and flavours, which extract at different rates, so there is no universal extraction time that applies to all coffees. You will need to taste your coffee at various extraction times to find the best result. 

What’s interesting is that extraction time only controls what types of solubles are dissolved and not how much. The only way to increase the amount of soluble flavours is by increasing your dose. As a simple rule, more coffee equals more solubles. Figure 2 demonstrates the impact of time and dose on flavour extraction. 

strong coffee
Figure 2: Time affects what flavours manifest while dosage affects their strength.

Along the horizontal axis, from the blue to purple cup, you can see how the increase in extraction time results in more solubles being dissolved.

But after a certain point, you start getting bitter flavours in your cup (the grey shapes). The idea is to pick the time where you are absorbing only the good solubles, in this case, the pink cup. Upon tasting this cup, you will find a good balance of acidity, sweetness, and roundness. 

Now, keeping the extraction time fixed, we can see how changing the dose impacts the taste in the cup.

If you lower your dose, although there is a good mix of solubles, it will most likely taste weak. The flavours in the green cup are more transparent, but will be drowned out in milk-based coffee. In the red cup, the dose is increased to allow more solubles in the cup, making it more intense and bigger on body. This will make the red cup stronger and ideal for milk-based coffee. 

However, if you continue increasing the two variables, the flavour decreases and can even have an inverse impact. You need to identify when you reach peak flavour and lock in the variables.

strong coffee
Figure 3: Different solubles are brought out of the coffee at different extraction times.

As a barista, your goal is to chase that flavour peak and continually adjust your variables to make the best coffee possible. Learning to control this combination of brew ratio, dose, and extraction time can do just that. 

This article appears in the August edition of BeanScene Magazine. Subscribe HERE.

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