Tweet
Found this fascinating article by James Grierson (Galla coffee) while Googling around, it has a number of illustrations that clarify things, cant post a link as its a UK based commercial site, however do a search for Galla coffee and you should find it.
What is Under and Over-Extracted Coffee?
It’s something the coffee industry is obsessed with (and its something I talk about a lot too). But what is under-extraction and what is over-extraction? To put it simply, it’s a taste perception. We call coffee that tastes: flat, boring or lacks flavour; as under-extracted and coffee that tastes: burnt, bitter or overpowering as over-extracted.
To be more exact, around 30% of the grounds we use to make coffee are soluble in water. But not all of this 30% is desirable. There are flavours we would rather leave behind as they don’t taste so good.
Since the 1950s various coffee related bodies have conducted studies into consumer preferences to coffee and it’s been found that an 18-22% extraction range is the most popular. So we could say that anything below this range is under-extracted and anything above as over-extracted. However, taste is a personal perception and there would have been people in these studies who found coffee at a 16% extraction tasted good and coffee at 20% over-extracted.
How Flavours are Extracted from Coffee?
The different flavours that make up your cup of coffee all have different levels of solubility. Some extract quickly, others extract much slower. Ted Lingle identified four broad groups of solubility based on the molecular masses of each flavour.
flavour groups in coffee
If you imagine that these different groups of flavour form an orderly and patient queue, waiting to be extracted. Only after the previous group has been fully dissolved can the next group start. So the first flavours are ‘delicate’, then ‘mid-tone’, followed by ‘sweet’ and finally ‘bitter’. Think of the bitter group as that last 8% of solubles in coffee (i.e. from 22-30%).
mug_shot
The Sweet Spot
Extraction is more to do with the balance of flavours than simply the strength of the coffee solution. This is why things can get a little bit complicated. If we use too little coffee then the solution has a weak taste, but it’s the bitter flavours of over-extraction that we will detect. If we use too much coffee then the solution will have regular strength, but we be lacking in flavours. Some coffees with fruity notes may even taste sour or sharp, like unripe fruit, if under-extracted.
Imagine we had a specific volume of hot water which has the capacity to dissolve 12g of coffee solubles in a 4 minute brew time and we assume that all four groups of solubles are of equal size. If we use only 40g of coffee then are cup will contain 3g of solubles from each group (i.e. 30% of 40g divided by 4).
over-extracted coffee
But if we use just over 53g of coffee we avoid over-extraction as the water will have been too preoccupied extracting the first 3 groups of flavours to have time to dissolve the final group.
perfectly extracted coffee
And to complete the set, if we used 80g of coffee we’d end up with under-extracted coffee.
under-extracted coffee
A good starting point on how much coffee to use is 60g per 1ltr of water. You can use our coffee calculator to calculate the exact quantity of coffee by entering the volume of water you’re using.
Uneven Extraction
Now that you understand extraction its time to throw a spanner in the works: a cup of coffee can be under and over-extracted at the same time!
Your cup of coffee is made from hundreds of coffee grounds. So when we brew, rather then one big (all encompassing) reaction we have hundreds of tiny reactions between water and each individual ground. As well as variations in each ground’s size (grinders produce a range of sizes rather than one uniform size); factors inside the brewing device will affect the speed of extraction. So some grounds will be extracted from quicker than others leading to some being under-extracted and others being over-extracted.
Is this something we should worry about? Personally, I think not. While we can take steps to minimise the differences in extraction rate it would be impossible to ensure a completely even extraction. The best we can do is concentrate on how the overall cup tastes and make adjustments from there.
What is Under and Over-Extracted Coffee?
It’s something the coffee industry is obsessed with (and its something I talk about a lot too). But what is under-extraction and what is over-extraction? To put it simply, it’s a taste perception. We call coffee that tastes: flat, boring or lacks flavour; as under-extracted and coffee that tastes: burnt, bitter or overpowering as over-extracted.
To be more exact, around 30% of the grounds we use to make coffee are soluble in water. But not all of this 30% is desirable. There are flavours we would rather leave behind as they don’t taste so good.
Since the 1950s various coffee related bodies have conducted studies into consumer preferences to coffee and it’s been found that an 18-22% extraction range is the most popular. So we could say that anything below this range is under-extracted and anything above as over-extracted. However, taste is a personal perception and there would have been people in these studies who found coffee at a 16% extraction tasted good and coffee at 20% over-extracted.
How Flavours are Extracted from Coffee?
The different flavours that make up your cup of coffee all have different levels of solubility. Some extract quickly, others extract much slower. Ted Lingle identified four broad groups of solubility based on the molecular masses of each flavour.
flavour groups in coffee
If you imagine that these different groups of flavour form an orderly and patient queue, waiting to be extracted. Only after the previous group has been fully dissolved can the next group start. So the first flavours are ‘delicate’, then ‘mid-tone’, followed by ‘sweet’ and finally ‘bitter’. Think of the bitter group as that last 8% of solubles in coffee (i.e. from 22-30%).
mug_shot
The Sweet Spot
Extraction is more to do with the balance of flavours than simply the strength of the coffee solution. This is why things can get a little bit complicated. If we use too little coffee then the solution has a weak taste, but it’s the bitter flavours of over-extraction that we will detect. If we use too much coffee then the solution will have regular strength, but we be lacking in flavours. Some coffees with fruity notes may even taste sour or sharp, like unripe fruit, if under-extracted.
Imagine we had a specific volume of hot water which has the capacity to dissolve 12g of coffee solubles in a 4 minute brew time and we assume that all four groups of solubles are of equal size. If we use only 40g of coffee then are cup will contain 3g of solubles from each group (i.e. 30% of 40g divided by 4).
over-extracted coffee
But if we use just over 53g of coffee we avoid over-extraction as the water will have been too preoccupied extracting the first 3 groups of flavours to have time to dissolve the final group.
perfectly extracted coffee
And to complete the set, if we used 80g of coffee we’d end up with under-extracted coffee.
under-extracted coffee
A good starting point on how much coffee to use is 60g per 1ltr of water. You can use our coffee calculator to calculate the exact quantity of coffee by entering the volume of water you’re using.
Uneven Extraction
Now that you understand extraction its time to throw a spanner in the works: a cup of coffee can be under and over-extracted at the same time!
Your cup of coffee is made from hundreds of coffee grounds. So when we brew, rather then one big (all encompassing) reaction we have hundreds of tiny reactions between water and each individual ground. As well as variations in each ground’s size (grinders produce a range of sizes rather than one uniform size); factors inside the brewing device will affect the speed of extraction. So some grounds will be extracted from quicker than others leading to some being under-extracted and others being over-extracted.
Is this something we should worry about? Personally, I think not. While we can take steps to minimise the differences in extraction rate it would be impossible to ensure a completely even extraction. The best we can do is concentrate on how the overall cup tastes and make adjustments from there.
Comment