Coffee Strength

Sep 17, 2020

We often get asked to recommend a coffee based on its strength. Traditionally the coffee industry has added strength guides to bags which over the years have become embedded in our minds. We perceive some coffees to be stronger than others so it makes sense to contact a roaster to ask which is their strongest coffee.

The answer for a contemporary specialty coffee roaster isn’t that easy and to explain why we’ve put the concept of a strength guide to the test.

We purchased three bags of coffee from the supermarket, all from the same company and all wholebean. Each was a different strength guide (3, 4 and 5). It would be fair to assume that the coffee labelled Strength Guide 5 would produce a stronger coffee than that labelled Strength Guide 3.

What is strength?

The strength of a cup of coffee is the amount of dissolved coffee solids in the cup. The beverage you drink will be part water and part dissolved coffee solids1. The more coffee solids which are dissolved into the cup, the stronger the coffee will be.

Measuring strength

We can measure the strength of a coffee by using a coffee refractometer. This device will give us a strength reading in the form of a percentage.

Brewed coffee will be somewhere around 1.3% strength.

In other words 1.3 parts coffee to 98.7 parts water.

Many people are surprised by these figures and it just goes to show how important the quality of your water is!

Generally a brewed coffee will be somewhere in the range 0.8 to 1.8% strength.

An espresso will typically be in the 8 to 12% range. The recipe we use at the Roastery (18g dose to a 36g yield), gives us an espresso around the 10% strength mark.

In other words 10 parts coffee to 90 parts water.

Testing Strength Guides

We brewed each of our coffees using a filter brewer as we felt it would give the most consistent results. Each coffee was brewed three times.

For batches 1 and 2 we used an EK43 grinder and Fetco batch brewer, using 85g coffee to 1.5 litres water.

For the third batch we used a Wilfa Uniform grinder and a Moccamaster brewer, using 28.5g coffee to 0.5 litres water.

The Results

Strength 3 Strength 4 Strength 5
Batch 1 1.37 1.21 1.3
Batch 2 1.31 1.18 1.18
Batch 3 1.31 1.29 1.29
Average 1.33 1.23 1.26

Across all brews the strongest coffee each time was Strength 3 which seems completely at odds with the information on the bags. So what is going on?

The real intention of the strength guides becomes apparent if you taste the coffees side by side. Strength 5 tasted much more of roast than the other two; it had a much more bitter flavour profile. And that is pretty much what strength guides refer to – the degree of roast and how much the flavour in the cup is influenced by the roast. It has nothing to do with actually producing a stronger coffee.

Influencing Strength

There is a really simple way to influence the strength of a coffee: grind finer or coarser.

To increase strength you need to increase the amount of dissolved coffee solids in the cup. A finer grind will achieve this.

Similarly a coarser grind will make it harder for the water to dissolve solids and you will end up with a weaker brew.

There comes a point, however, where altering the grind not only impacts on strength but also has a negative impact on the quality of the coffee. Some of the solubles in your coffee don’t taste great and can leave a bitter, drying tone to the finish. This is called over extraction. It is possible to grind too fine, causing this over extraction.

A bad tasting coffee can also be due to under extraction. If your grind is too coarse you might not dissolve enough solids to balance the coffee and it won’t be an enjoyable experience.

A final point on the amount of coffee

Many people who want a stronger coffee will usually updose their brew. In other words they will use more coffee. While this can indeed impact on strength (more coffee equals more available solids to dissolve into the cup), there again comes a point where this can a negative impact.

For brewed coffee we generally recommend around 60g coffee per litre of water.

For a weaker brew you might drop as low as 50g coffee and for a stronger brew aim for 70g per litre.

This deserves a bit more explanation but we’ll save that for another post!

  1. Some coffees also include a percentage of suspended particles in the cup, most notably espresso and coffee brewed using a coffee press.
Coffee Strength via @carvetiicoffee