- Texture, weight or viscosity
- Concentration of dissolved coffee flavour.
These three things are also regularly part of the same sentence, so to avoid confusion, here’s how I’m going to write about it:
When I use the words ‘strength’, ‘strong’ and ‘weak’ I’m talking about the concentration of dissolved coffee flavour, or Total Dissolved Solids (TDS).
When I use the words like ‘rich’, ‘watery’, ‘heavy’ and ‘light’ I’m talking about texture, weight and viscosity.
To communicate strength quickly and effectively, we refer to it as a percentage of the total brew. Most espressos will be somewhere between 7% and 12% strength which means they contain anywhere from 88 to 93% water. Drip/filter style coffees are typically between 1.2 and 1.8% coffee, which means they contain between 98.2% and 98.8% water.
“98.8% water?!” you ask? Well, yes. Water may be the main ingredient in coffee, but it’s certainly not the most obvious. Coffee is an incredibly intense flavoring agent. Very small variations in strength are easily identified by our palates. Changes of just 0.1% strength are detectable to anyone with observant taste buds. This means that espressos sitting at either end of the spectrum (7-12%) can produce experiences that are worlds apart.
An espresso can be 10 times stronger than a drip/filter coffee. This almost guarantees an increase in perceived flavour intensity because there’s 10 times more flavour compounds hitting your tongue. Although it’s not just a simple increase like turning up the lights.
Strength also affects our perception of flavour. There is a very obvious reduction in our ability to identify a coffee’s flavours as its strength increases. There is also a rapid increase in the perceived intensity of a coffee’s flavours at higher strengths. Even though the coffee contains the same flavours, your palate will interpret them differently at varying strengths.
Weaker coffees aren’t necessarily watery or insipid. Sometimes, a lower strength can allow our palate to enjoy more subtle flavours that would be hidden by a higher strength. A lighter, more delicate espresso is less intense and sometimes much more drinkable than a strong one.
Stronger espresso brews will affect our ability to taste the coffee’s natural flavours. The best way to experience this is to make a short, strong espresso with a traditional darker ‘espresso’ roast, then dilute it to varying degrees with water. At the initial high strength, you might be fooled into thinking the roast isn’t so dark. Once diluted, you’ll easily taste flavours produced by the roasting process that were not as obvious before.
At a certain strength, no matter what the coffee is or how it was made, a coffee will become intensely bitter and unbearable. Unfortunately, our tongues just haven’t evolved for accurately tasting liquids at high concentrations. If you’re wondering whether the cause of a shot tasting bitter is strength, dilute a portion of the drink with water to check. If it goes away, strength was the culprit. If it stays, there’s another problem.
Texture, Weight and Viscosity
Tactile elements are some of the most important aspects to a good coffee. When tasting a coffee, everyone is expecting a certain level of texture, weight and body. These preferences vary greatly according to location and culture, but it’s fair to say that an espresso should generally be viscous and mouth filling to satisfy most tastes. A drip/filter coffee should also have reasonable heft and texture, lest it be classified as insipid water.
Here’s a spectrum of words I use to classify a coffee’s strength, in order from too weak to too strong. Some of them can be used to describe flavour intensity, but the words and their order displayed here are purely in regards to the texture, weight and body afforded by strength.
This list isn’t exhaustive, but should afford you a pretty broad range of words to describe the strength of any coffee you encounter.
The Perfect Strength
Like most subjective aspects of coffee, the perfect strength is hard to define. Everyone wants something different out of their beverage. For me, an ideal strength provides a fulfilling mouthfeel and viscosity but doesn’t detract from the flavours provided by your extraction. These are the ranges of strength I like to sit in.
For espresso, this means anywhere from 7.5-9.5%TDS. Strengths higher than this make my palate send considerable bitter signals to my brain. Anything lower and you’re entering the relatively undiscovered (but delicious) realm of 2-7% strength. Coffees in here are hard to define as either filter or espresso no matter how they’re brewed. If you’re serving an espresso that’s lower than 7%TDS it’d be best to set some expectations about texture and weight before a customer gets it.
For drip/filter, I prefer anywhere from 1.3-1.7% TDS. Any weaker than 1.3% just isn’t satisfying for me. It lacks heft and really leaves me wanting more flavour. Coffees around the 2% mark are also weirdly disappointing. I feel like there’s peaks and troughs of deliciousness as you move through coffee strengths and 2% is right in the middle of a trough. It’s too strong to be drip/filter and not strong enough to be a satisfying americano.
As always, experimentation is king. I think learning about and experimenting with strength as an independent variable is absolutely crucial for all baristas.
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