5 Apr 2018 · 4 min read

Coffee and Strength – What is a Strong Coffee?

By Keiran Jones

"I like a really Strong Coffee!"

I hear this sentence and the misuse of the word strong rather frequently. Whereas some people might grasp the meaning, many within the coffee industry could misunderstand. It matters because even amongst coffee lay people, the definition of strength is not clear. Is the speaker referring to the darkness of the roast and therefore bitterness? Or are they speaking about the caffeine content of the coffee (which we’re unlikely to taste)? Or is it the intensity of the coffee, like the mouth shock delivered by espresso? There are many ways to interpret strength but in seeking to improve a coffee experience, particularly at your local shop, it is important to use the correct terminology to be correctly understood.

Note – Some of this is a little advanced. Key summary points are at the bottom.

Put simply, it is the percentage value of coffee molecules in a volume of liquid. To explain this further, an espresso is far more concentrated than a filter coffee. The former stronger than the latter. We can dilute the espresso with water until it becomes weaker than the filter coffee.

It is not the bitterness of the coffee. It is not the darkness of the roast (as many commercial coffee companies term it). You can test this simply with instant coffee. It might have a strength rating relating to the darkness of the roast. You can add half a teaspoon of coffee to one cup and five to another. After filling them up with the same amount of water you will not experience the same strength of coffee, despite the strength rating given on the packaging.

What does a strong coffee taste like?

Espressos and ristrettos are the strongest commonly consumed coffee drinks. They typically exert intense sensations in the mouth and it can be difficult to determine flavour. There is a heavy or syrupy feeling in the mouth. Flavour becomes easier to perceive with the addition of water, like with an Americano. This happens as the basic taste senses are not as overwhelmed by the strength of the coffee.

Pour over filter coffees are much weaker than espresso. Flavours are easier to determine and the taste sensations are less pronounced.

For those who are interested:

Typical espresso strength – 10% of volume is coffee solids

Typical filter strength – 1.4% of volume is coffee solids

These percentages are measured with refractometers. Although these figures are considered ideal, they may not reflect a perfectly brewed coffee as they measure dissolved solids, not the kind of molecules. Down the rabbit hole you go.

Is strength extraction?

No. Extraction is the percentage of soluble coffee solids dissolved into water. Around 30% of a coffee’s weight is soluble – that is, it can be dissolved in water. The rest is non soluble. It may not be ideal to extract that full 30% though as some molecules don’t taste great. The SCA state that an extraction yield of 18-22% is ideal, based on data collected on taste preferences. However, this number is an average. Some of the coffee grounds might be extracted to 28%, and others to 14%. This imbalance will not taste great and is why uniform grind sizes so important.

Does a strong coffee relate to caffeine content?

Not necessarily. Espresso is stronger than a filter coffee. However, 20g of coffee might be used for an espresso but 30g are used for a filter coffee. Caffeine is extracted early on in the process and so the drink which was made with more coffee will have more caffeine. This is why cold brew is said to be so high in caffeine. The ratio of coffee to water is narrower (1:10, filter - 1:17), making a cold brew drink of equal volume to a filter more concentrated. Keep in mind this example assumes the same coffee is used.

Does water affect strength?

Absolutely. Distilled water with 0 Total Dissolved Solids (TDS) does not have the charges to attach itself to all the flavour molecules in coffee. Extraction yield will always be low and regarded as under extracted (but might still be strong if heavily concentrated). Magnesium and other chemicals and elements are needed for greater extraction. Too high a TDS also makes it hard to extract all desirable flavours as ‘space’ is reduced i.e. there are fewer available bonds for a reaction. Look for the goldilocks water, around 70-150 TDS.

Coffee strength is hard to measure and there are many other variables which might mask or influence sensory evaluation. Technology aids us in this measuring and in finding consistency but don't forget, if the coffee tastes good, be happy!