Introduction
Generally speaking, when it comes to broad sweeping statements and generalised questions, it’s awfully hard to get a direct answer out of anyone.
“What type of car is best for me?”,
“How many chefs should I hire for the kitchen space in my new restaurant?”
Often the answer is dependent on the unique circumstances of the situation. Sadly, brewing good coffee is no different, but for us, that’s where the beauty lies! In order to understand a little bit more, let’s talk about extraction theory.
Extraction Theory – What is Extraction?
I can already hear the crowd groaning… Not another pretentious coffee snob that’s going to overcomplicate something I do with my eyes half closed first thing in the morning.
Don’t worry, for those of you that haven’t already clicked away, we’re going to keep things easy to follow and informative.
When talking about extraction we are referring to which dissolvable (soluble) compounds you pull out of a coffee, how many of them you pull out, and the proportions at which they’re present in your final drink in comparison to each other.
Approximately 28% of coffee compounds are water-soluble, meaning you can dissolve up to 28% of the coffee grounds you use, into your cup. (Hustle, n.d.)
A flavour wheel depicting flavours extractable from different types of coffee. (Coffee, n.d.)
Measuring Extraction – Taste
At the end of the day, how much you aim to extract from a coffee comes down to your taste preferences, but most would prefer what they consider to be a ‘balanced extraction’.
Balanced extraction: The acidity and sweetness levels in the coffee are in present in similar quantities, with minimal bitterness. There’s a lingering pleasant taste.
When looking to achieve a balanced extraction, it’s helpful to understand which flavours you can find in coffee and how to identify them, to help you troubleshoot when things aren’t tasting too good. The ones we need to focus on are the acidity, sweetness & bitterness of coffee.
Sweetness
Simple sugars present in unroasted coffee called monosaccharides are bonded together in roasting via the Maillard reaction to form disaccharides (such as sucrose).
Use the preparation guide to make a sweet tasting sample, to taste as reference alongside coffees.
(Flavour Wheel , n.d.)
Acidity
Different acids are formed in coffee at different points during its life cycle. Malic, Citric and Succinic acids are formed as coffee cherries grow. Acetic acid is formed during the processing of these cherries at the farm. Many more acids are formed during roasting, one of the main ones being chlorogenic acid lactones.
Have a look below for some guides on how to isolate and taste an acidic or sour taste, so you can recognise it in a coffee.
(Flavour Wheel , n.d.)
Bitterness
During the roasting process, chlorogenic acid is converted into chlorogenic acid lactones through dehydration and cyclization. (PubMed Study, n.d.) It is these chlorogenic acid lactones that largely contribute to the bitterness that we taste in coffee. (Hendrick, n.d.) The more of the coffee we extract, and the more lactones present to begin with, the more likely it is that we will taste this bitterness. Caffeine also has a naturally bitter taste.
(Flavour Wheel , n.d.)
How do Acidity, Sweetness and Bitterness change Depending on Extraction?
We know what flavours to look out for in coffee now, some good, some… not so much (for those of you that did some tasting or have ever had a really bad espresso – ouch).
What we don’t know is how to alter their balance in each cup in order to achieve the perfect harmony of flavour. Now this – is where we can start to look at how grind size comes into play.
When we extract less out of a coffee, since the flavour compounds with a more acidic taste are the most soluble, we tend to taste these more since they’ve dissolved into our cup in a higher quantity than anything else. When we don’t extract enough out of a coffee and get mostly acidic tastes, it’s ‘under-extracted’, and likely watery or weak too.
The opposite happens when we extract too much from a coffee – the bitter flavour compounds dominate the taste and any pleasant acidity isn’t notable. When coffee tastes bitter in this way we call it over-extracted.
(Coffee Extraction & How to Taste it, n.d.)
A large impactor on how much we extract out of a coffee is the grind size.
(88 Coffee Company, n.d.)
Grind size
Imagine a whole coffee bean. If we take that same bean and split it in half, not only is the whole of the exterior still exposed, but now the interior of the bean is also exposed. If we now take those two halves and split them again, even more of their contents will be exposed.
The same happens when we grind a bean down and make it finer. More and more of its surface area is exposed, which increases its potential to come into contact with water and be extracted.
By grinding beans finer, we can increase the amount we extract out of them.
What does this all mean?
Now we know how grind size impacts extraction and how extraction impacts flavour, we can tie the two together.
If a coffee is under-extracted, weak or sour or even both (hopefully not), then we need to extract more of the sweeter compounds out of the coffee. We can achieve this by grinding finer to increase the surface area of the coffee grounds, so that more of them come into contact with the water.
In an opposite scenario, where the coffee tastes bitter, ‘muddy’ and doesn’t have any pleasant acidity, we’ve extracted a bit too much out of it. We’ve ended up with too many of those bitter tasting flavour compounds, and too many dissolved coffee grounds in the cup and we need to grind courser.
These concepts surrounding extraction are the fundamentals of all brewing, whether its French press (cafetiere), AeroPress, V60 filter coffee or espresso, or even something else (check out siphon coffee brewers if you haven’t heard of those before!). When you run into a coffee you don’t like, have a taste, evaluate whether or not it’s under or over extracted and make the relevant grind size adjustment.
For those of you using pre-ground coffee, I’d recommend getting it ground at your local coffee shop where they can fine tune the grind size for your specific preferences depending on how you found it previously.
(Coffee Grind Size Chart Guide, n.d.)
References
88 Coffee Company. (n.d.).
Retrieved from 88 Coffee Company: https://88coffeecompany.com/blogs/manifest-greatness-blog/coffee-grind-size-chart
Coffee Extraction & How to Taste it. (n.d.).
Retrieved from Barista Hustle: https://www.baristahustle.com/coffee-extraction-and-how-to-taste-it/
Coffee Grind Size Chart Guide. (n.d.).
Retrieved from Big Cup of Coffee: https://bigcupofcoffee.com/coffee-grind-size-chart-guide/
Coffee, S. T. (n.d.). Sci TH Coffee.
Retrieved from https://www.scith.coffee/wp-content/uploads/2021/03/SCA_CoffeeTastersFlavorWheel_A4_English_Secured.pdf
Flavour Wheel . (n.d.).
Retrieved from Not Bad Coffee : https://notbadcoffee.com/flavor-wheel-en/
Hendrick, L. (n.d.). Lance Hendrick Youtube.
Retrieved from Youtube: https://www.youtube.com/watch?v=Z2zsmehysHk
Hustle, B. (n.d.). Coffee Extraction and how to Taste It .
Retrieved from Barista Hustle: https://www.baristahustle.com/coffee-extraction-and-how-to-taste-it/
PubMed Study. (n.d.).
Retrieved from PubMed: https://pubmed.ncbi.nlm.nih.gov/27719962/#:~:text=Chlorogenic%20acid%20lactones%20have%20been,the%20chlorogenic%20acids%20(CGAs).