Deep Dive: Coffee Strength
I face this discussion on almost a daily basis.
Someone asks me, “How strong is your coffee?”
In truth, it upsets me. The notion that all of the hard work put into making coffee, by various actors across a complex supply chain, can be ignored for the sake of some caffeine “rush” is saddening. I want coffee to be delicious.
Below I’ll unpack the concept and misconceptions of coffee strength. Hopefully I’ll manage to put this one to bed, once and for all.
If I’ve sent you here directly, after we’ve had a face to face conversation; welcome.
The notion of strength in coffee is bifold. It’s constituents are:
*To read my summary of this long post click here.
It’s worth mentioning, before all else, that these two aspects are not intrinsically linked. Contrary to common belief, caffeine contributes little to coffee flavour. Drinks both with and without caffeine can be hard to distinguish through taste alone. Knowing this allows us to separate these two notions entirely and from there we can create greater understanding.
Strength of Flavour
Without rehashing my post on flavour too much; understanding the strength of coffee flavour can be troublesome.
Whilst strong coffee flavour isn’t something I believe should be a goal for consumers, it is a reality. It is generally modulated as thus:
Coffee Roast Degree - This is the most common and often misconceived idea of coffee strength. As coffee is roasted its chemical structure is broken down through a series of complex reactions. At some point, caramelisation of compounds turns from producing rich toffee like flavours into burnt heavy notes. There is a balance to play here, much like the one we find when making toast. Wrongly, tradition states that the strength of a coffee is controlled by the darkness of the roast, with roastier flavours being associated with a stronger cup.
Whilst darker roasting may give some perceived strong flavours it doesn’t necessarily deliver the best flavour to our drinks, simply the roastiest. It’s easy for a coffee roaster to take one coffee; roast it in multiple ways and sell it as any number of “strengths”, one simply has to run the roaster for longer/hotter to vary their output. It’s a much harder thing, however, for a roaster to buy a variety of coffee and showcase interesting or unique characters based on their production. As discussed in my other posts, I’d welcome a departure from this school of thought.
Coffee Brew Strength - A more legitimate means of varying strength in coffee is much more poorly understood and communicated.
Roasted coffee can never be fully dissolved, otherwise we wouldn’t be left with coffee grounds after brewing. Only a portion of coffee is soluble and only some of that will end up in our drink. Many factors affect the percentage of coffee that is actually dissolved when we brew and an understanding of how to manipulate these variables is crucial in brewing great coffee, we’ll get to that in further blog posts.
Let’s examine the most fundamental controls we have for altering brew strength: the dose and yield of our brew.
Take two coffees; in one we’ve used 20g of coffee to brew a small cup, the other only 10g. Provided the resulting drinks are the same size and our brews have similar extraction efficiency, the one with a 20g dose will brew a stronger coffee than the 10g dose. Whilst this result is intuitive and not very surprising we can extend it as follows. It is also the case for any two differing coffees, regardless of roast level. That means a 10g dose of an Italian style espresso roast would brew weaker than a 20g dose of light roast coffee; the way it tastes is not a variable in this equation. The message is this; if you’d like your coffee to be stronger; use more coffee or less water.
Quantity of Caffeine
Now that we’ve separated the contribution of flavour and caffeine to our drinking experience it’s possible to analyse the quantity of caffeine in coffee beverages.
There’s one quick notion to dispel before we move on; barista lore has it that: caffeine is readily and easily dissolved. Whilst it is true that pure caffeine is relatively soluble, caffeine in coffee is different. As with all compounds in coffee, it is trapped inside a complex cell structure and getting it out is subject to the brewing process. Whilst I advocate for efficient brews achieving them is not necessarily straight forward. The concept that caffeine dissolution was one hundred percent efficient, would mean that for any two brews given the same dose of the same coffee, the caffeine content would be equal. Studies however have found this not to be true. In actuality there is a link between extraction efficiency and caffeine dissolution. Other studies concerned with caffeine extraction for pharmaceutical or other downstream uses assert this too.
The second issue to address is, how roasting affects caffeine content in coffee. It’s said that caffeine content is stable throughout coffee roasting; this conclusion can be hard to test. Due to the significant complexity of the roasting and brewing process, studies with reliable results few and far between. Through my reading, I’ve concluded; caffeine content is affected by the roasting process but not significantly. I believe the significant effect of coffee roasting on caffeine is actually a result of the change in density for darker roasts. Since each bean is less dense and we measure brews using mass, the resulting brews from more developed roasts should have more caffeine to extract. The caveat here is that darker roasts are typically extracted less efficiently. Since the flavour of high extractions with dark roasts is deemed unpalatable, we generally find less of the available caffeine actually in the cup; resulting in less caffeine than first anticipated. Whilst I’ve found no studies for exact quantities of caffeine in brews of various extraction efficiencies of various roasts, the diminished effect of these variables makes it of little importance.
Summary
To summarise: caffeine content in a cup of coffee is a product of the extraction efficiency vs roast degree of its ingredients. Light roasts with high extractions and dark roasts with lower extractions both having similar caffeine content.
Let’s consider how all of this affects the everyday consumer.
When looking to answer the question “Is this coffee strong?” we need to consider our values.
The conclusions below aren’t surprising, there’s a self-evident link between using more coffee to brew a drink and it being stronger. I’ve tried to answer the two most obvious questions as straightforwardly as possible.
However I’d like to suggest a third, probably braver answer. I want us all to aim to have the best tasting coffee. I’m under no impression that this is an easy journey and for some it’ll push away from comfort and familiarity; the hope is that it’s worth the effort. Moreover, this approach lends itself to the ideals I’ve laid out in my posts on coffee ethics and contributes more to the coffee supply chain than simply maximising an arbitrary preference.
If the aim is to get as much caffeine as possible: Choose a darker roast, extract more from your coffee or use more coffee to brew the drink.
If the aim is to have the strongest flavour: Use more coffee to brew the drink.