Under-Extracted & Over-Extracted Coffee. Understanding The Differences
We hope that you may notice when reading the GUSTATORY Journal & School that we really want to make speciality coffee accessible, straight forward and hassle free for home-use. We don’t believe a good coffee should be reserved for coffeeshops and we’re here to guide you through the fundamentals whilst sharing insights and knowledge to help you brew the best cup of coffee possible.
In this article we’re focussing on espresso coffee, which is arguably the fiddliest brew method to get right with grind size being one of the most crucial determining factors - amongst other things of course. However, if you get the grind size right then you’re most of the way there. Then you may need to consider things like water pressure and extraction time but we’re not going to focus on that in this article.
In another recent article we explore the importance of choosing the right coffee grinder, and there we recommended purchasing a burr grinder, of which for espresso in particular, you really should make sure your grinder is able to grind the coffee finely - the finer the better. But how fine is fine? That’s a good question and it can be tricky to determine when you’re just starting out but here are some points to consider.
The reason we recommend a burr grinder is you’ll achieve more uniformity in terms of the grounds. This is important because it will ensure the water passes through the portafilter evenly which aids an even, consistent extraction. If grounds are different sizes then some of the water will pass through quickly and this will lead to an under extracted shot of espresso. Trust us, you don't want to achieve this.
1 Under-extracted coffees
With espresso coffees, under-extraction normally occurs when the grounds are too coarse. This allows water to pass through the grounds too quickly leading to less of the coffee being properly extracted. But how do you tell if your coffee is under-extracted and what can you do about it?
Tasting the espresso shot is the only real way to determine this and we recommend pulling a few shots when adjusting your grind size so you can fine tune before adding milk. Typically speaking, under-extracted coffee is normally very acidic tasting and can be best described as sour. If you experience any sourness and acidity when tasting your espresso then you should adjust your grind size. The best thing to do is to grind the coffee finer and repeat the process and incrementally adjust the grind size to a finer setting as you go. Simple.
2 Over-extracted coffees
Conversely, grinding your coffee too fine will lead to what we call over-extraction. This occurs when the coffee grounds are so fine that the water is unable to adequately pass through the coffee grounds quick enough. As a result, this leads to too much flavour being pulled out of the coffee and it leads to a rather unpleasant shot.
Tell tale signs of over-extracted coffee are bitterness or even very little flavour at all. If you read the tasting notes that are typically published on your coffee wholebeans packaging then you should be able to at least subtly identify these flavours in your shot. Chocolate notes should be comforting and smooth, whilst fruity notes should be crisp and sharp, and if you’re not getting any of those characteristics and it just tastes like a hot, bitter drink then chances are you’ve ground too finely. Simply adjust your grind size to make it coarser and you should start to see those tasting notes come back.
For other brew methods such as an Aeropress, V60 or cafetiere, other factors can aid this ratio of grind size to flavour. These include brew time and water temperature, and to learn more about these, please do have a read of our Aeropress Brew Guide, V60 Pour Over Brew Guide or cafetiere Brew Guide. In this article, since we’re only talking about espresso and with many consumer-grade domestic espresso machines providing very little customisation functionalities when it comes to water temperature, we feel achieving an accurate grind size is the best way to achieve consistent results.
If your espresso machine does give you the option to adjust the shot time or the extraction time then you can also experiment with this. A shorter extraction times can lead to under-extraction and a longer extraction time can lead to over-extraction - this makes sense, right? - but the default setting on your machine should always be a safe starting point. It is important to note that every grinder and espresso machine is different, and beyond the advice we publish in our Journal & School, your machine may come with their own instructions and advice. On this, we always recommend buying a quality espresso machine or coffee grinder that has been designed and manufactured with speciality coffees in mind - the brands that manufacture these will know that speciality coffee comes with it's own nuances compared to commodity coffee, and their designs take this into account. But, with a little time of owning and experimenting with your machine, you’ll be pulling perfect shots before you know it.
GUSTATORY (adjective): curating excellence in taste.