# Over/underextraction, what does it actually mean?



## Neill (Jun 26, 2013)

This is maybe something the refractometer boys can explain with hard figures.

Ok so I've been at this a while and understand the basic principles (or do I?). Underextraction is pulling less than an ideal amount of dissolved solids from your coffee and the opposite for overextracting. Under will be pale, sour and thin. Over with be thick, dark spots in crema and bitter.

What I want to know is are we all using these phrases correctly and to describe the same thing? How much does shot concentration come in to play. For example, I pull a shot from 20g with the grind too tight and only get 10g out in 30s. I would have called that overextracted, but is it? Could this be underextracted because less water has been through the puck to pull dissolved solids with it but too concentrated due to the volume. If I added 25g of hot water to it would it taste any better? How easy is it to actually over extract a shot based on refrac figures? I suspect most of my shots that don't taste great are actually underextracted and sour.


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## The Systemic Kid (Nov 23, 2012)

There's a finite amount of dissolvable solids in the puck - the challenge is to get as much into the cup as possible. Under extracted shots taste sour because the acids in the grind are the easiest elements to extract and do so in the early part of the extraction. Getting the sugars - sucrose out is more of a challenge and when extracted efficiently is at the cost of increased bitterness from the fines present in the puck. As for pulling a shot where you're only getting 10grms out from a 20grm dose, guess you would find that if you refracted it, the TDS would be higher than for a normal pull but as the brew weight is so low, when extraction yield is measured, it would be poor, i.e. low.


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## Mrboots2u (May 10, 2013)

Regarding " official figures "

Each specialty coffee association I think had it's own recommendations for extraction ranges ( they do differ slightly )

Glenn or someone else may be able to explain how theses are arrived at

They are generally around 18-22 % EY for espresso , not that , the means someone can't enjoy a drink that isn't in this box , it's not the law , it just the measurements across that area , personally I prefer sweet espresso ( no sugar ) and love it when I can hit the upper reaches of EY

One below is SCAE box


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## Neill (Jun 26, 2013)

The Systemic Kid said:


> Getting the sugars - sucrose out is more of a challenge and when extracted efficiently is at the cost of increased bitterness from the fines present in the puck.


This is exactly where I was going with that question. That bitter shot that most people describe as overextracted. Based on measured figures presumably isn't actually over extracted, just has too many fines to taste ok.


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## MWJB (Feb 28, 2012)

The different associations have specific regions for concentration/strength of brewed coffee, but all typically target 18-22% extraction yield. This range was arrived at following consumer research & has subsequently been reinforced over the years & has been found to apply to espresso too. An alternative study previously carried out amongst coffee professionals was a little lower in range at 17.5% to 21.2%, so as Boots says, there may be factors that shift the outer margins of the range slightly. The "big hump" in preference is typically considered to be ~18.5% to ~20.5%.

EY indicates flavour balance and is related to concentration at specific ratios, otherwise a well extracted coffee could be anywhere from 1.15%TDS to 14.00%TDS, maybe more?

So Neill, you're probably right, as Patrick says, that very short & bad tasting shots are underextracted rather than over...it's a common misconception that anything that is overly pungent is "overextracted", it can happen but you have to push a certain amount water through the puck to overextract, the more water used (weaker the coffee) the higher this possibility becomes. There can often be bitterness in underextracted coffee, so sour/bitter doesn't always follow.

There are ranges where technically underextracted coffee isn't necessarily offensive (for some folk it is even typical), so try adding a bit of water if it is *just* the high concentration/pungency that is the problem, but this won't affect the sour/sweet/bitter balance...it'll just make what you have weaker.


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## MWJB (Feb 28, 2012)

Neill said:


> This is exactly where I was going with that question. That bitter shot that most people describe as overextracted. Based on measured figures presumably isn't actually over extracted, just has too many fines to taste ok.


You may also hear people talking about "overextracting the early part of the shot" or similar, to get a good result - this isn't really possible in the technical sense because extraction yield considers the average EY of the entire output. However, too wide a particle distribution/very high incidence of small/large particles can limit the overall good tasting yield due to overextraction of the smaller particles & underextraction of the larger particles. In these cases, a lower overall yield might be preferable to balance the flavour.

Without a refractometer, brewing by ratio (weight) is the next best method (really more of an extension of yield analysis, as this is how the targets of specific ratios were actually determined), using grind to fine tune EY and flavour balance.


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## Neill (Jun 26, 2013)

With all of the above taken in to consideration, is it time to move away from using the terms over and under extraction as many of us have with terms like ristretto and lungo.


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## DavecUK (Aug 6, 2013)

Well I bet all this has completely cleared it up for you


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## Mrboots2u (May 10, 2013)

DavecUK said:


> Well I bet all this has completely cleared it up for you


Why don't you give us an insight from your years of experience , and help the OP with his question


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## Neill (Jun 26, 2013)

I think DavecUK does make a valid point in a way. I think this area is much more complicated than is often suggested by the terms under and over extracted and we make it sound too simple by using those terms.


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## MWJB (Feb 28, 2012)

Neill said:


> With all of the above taken in to consideration, is it time to move away from using the terms over and under extraction as many of us have with terms like ristretto and lungo.


I don't think so, "normale" & "lungo" are totally subjective & if you weighed different people's lungos they would all come out differently.

Extraction yield is an objective measurement, if 20% of your dose has been dissolved into the coffee, then that is measurable & identifiable...there may be factors that shift whether that 20% suits your preference, but you now know what you have and, assuming solid technique, can decide on what remedial action to take.

A gross simplification (suspending real world factors for a minute) 20g of coffee with 20% dissolved in to a 40g shot means you theoretically have 4g of coffee in the beverage. It's 1/10th of the weight of the beverage so Total Dissolved Solids make up 10% of the shot...if it is brewed coffee and you have 267g of coffee, then 4g is 1.5%TDS. In reality it's not quite that simple but that's the gist of it.

The idea behind extraction yield as an objective measurement is that different coffees taste different. If one guy is brewing a coffee and raving about blueberry, it's no good saying coffee tastes good when it tastes of "blueberry", when your coffee tastes of chocolate & cherries. It's a universal measurement that applies irrespective of varietal & region.


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## Neill (Jun 26, 2013)

MWJB said:


> I don't think so, "normale" & "lungo" are totally subjective & if you weighed different people's lungos they would all come out differently.
> 
> Extraction yield is an objective measurement, if 20% of your dose has been dissolved into the coffee, then that is measurable & identifiable...there may be factors that shift whether that 20% suits your preference, but you now know what you have and, assuming solid technique, can decide on what remedial action to take.
> 
> ...


Yeah, I'm ok with extraction yield etc as they are objective measurements. What I do think sown of us get wrong is using the terms under and over extracted (as demonstrated by my original post).


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## MWJB (Feb 28, 2012)

Neill said:


> I think DavecUK does make a valid point in a way. I think this area is much more complicated than is often suggested by the terms under and over extracted and we make it sound too simple by using those terms.


The terms are often incorrectly used and in those cases are merely a substitution for "I don't like that", without necessarily specifically identifying why.


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## Mrboots2u (May 10, 2013)

Mainly you see " this coffee is way too sour " for example


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## Neill (Jun 26, 2013)

Mrboots2u said:


> Mainly you see " this coffee is way too sour " for example


But you then see three different replies to this statement on here-

Tighten your grind, it's under extracted.

Pull it a bit longer to bring more sweetness through.

Stop buying hasbean and move to italian job









I realise two of the above statements may be correct.


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## garydyke1 (Mar 9, 2011)

there is a standard chemex recipe which a few of us use at work. 30g dose , 500g water and aiming for 4 mins with 92.5c water.

Its not unusual to have two of us making brews at once and TDS'ing them.

person A will say ''yes I nailed mine , 1.26%'' (they enjoy 1.26-1.27 brews)

person B will say ''ah balls, over extracted mine 1.38%'' (they enjoy 1.29-1.30 brews)

Thing is we dont use the app or do the maths to work out actual Extraction yield. We know from the strength reading what the beverage is going to be like. If differing recipes were being used then TDS alone becomes less useful by itself .


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## DavecUK (Aug 6, 2013)

Neill said:


> I think DavecUK does make a valid point in a way. I think this area is much more complicated than is often suggested by the terms under and over extracted and we make it sound too simple by using those terms.


Yes, correct. You cannot simply sit there and pin labels on things. Just one example.

All the numbers are good, temperature is correct RI is correct, shot time was good, but it tasted bad.

1. Is it the coffee (possibly)

2. Is it the grinder (possibly)

3. Was it a single or double basket, 53mm portafilter or 58mm (might be)

4. Depth of the puck (could be)

5. Perhaps the water quality

6. perhaps the machine needs cleaning

Theres a whole heap of things that could be going on...the RI of the coffee will only tell you so much, the science can fail us as it is open to misinterpretation, often because the context the measurement is taken in is not controlled..With the refractometer the sample has to cool, so your not measuring the volatiles and who knows is the RI has a direct relation to volatiles in the cup. There are quite a few variables, many of the very important ones never discussed. So yeah, I bet the OP is no clearer, how can they be. If you start talking about refractometers, you have to know the OP has one, otherwise it's not really helping them, I also question whether refractometers help anyway?



Mrboots2u said:


> Why don't you give us an insight from your years of experience , and help the OP with his question


What no smiley face........


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## Mrboots2u (May 10, 2013)

I think he asked the refractometer boys for an opinion didn't he ?


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## DavecUK (Aug 6, 2013)

Mrboots2u said:


> I think he asked the refractometer boys for an opinion didn't he ?


In a sense yes and in a sense no Boots.



> This is maybe something the refractometer boys can explain with hard figures.


He wanted to know if refractometry explained it, but without one, it doesn't help him. Also, refractometry is incapable of explaining anything happening to his shots, based on the information available. It's simply one of those forum discussions that appear from time to time and will probably go nowhere. You should look at my post and think hard about what I said, instead of "nit picking". There are quite a few things in there, often overlooked.


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## Mrboots2u (May 10, 2013)

I read all those points . all of them to me will effect what a measured extraction yield is....not denying that .

Using a refract doesn't tell you why it is a number . it just tells you a number ....

What you do after that is up to you.

Some people can't tell whether something is " under or over " hence why measuring it can be helpful...

Op was asking what people meant by it..not what caused it .....


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## DavecUK (Aug 6, 2013)

Just got showered in nits again......


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## Mrboots2u (May 10, 2013)

OK dave we disagree thats. It really is fine. I've tried one way of answering the question.

All you've done is say why I'm wrong and be sarky..as per last answer. It doesn't actually mean anything or help anyone ..

All I really want is for you to offer an alternative , really . I have lots to learn and take in and i like listneing and debating points of view.

I haven't been intentionally been rude Dave. I'm just asking questions and trying to evaluate opinions and ideas ....

One if your posts was really interesting but is reasons why something may be under or over ..not how to judge it , or what it is

. all those things you mentioned will effect what ends up in the cup, which is what a refract measures. Refract doesn't know what water your using or basket size...

Or whether when one person says under extracted it means the same as another person

I'd genuinely like to know your approach ....


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## majnu (Jan 31, 2014)

Towards the end in the video he explains it a bit and summarizes what refraction means to him. Nice video, done by someone here I believe


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## Eyedee (Sep 13, 2010)

I thought the concept of "calibrating your taste buds" was interesting.

Ian


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## MWJB (Feb 28, 2012)

DavecUK said:


> Yes, correct. You cannot simply sit there and pin labels on things. Just one example.
> 
> All the numbers are good, temperature is correct RI is correct, shot time was good, but it tasted bad.
> 
> ...


1. A refractometer can actually help identify bad roast batches, if a given coffee has given good results previously, an underdeveloped roast, or component in a roast, might make itself known by no longer allowing you to hit a good yield. If we assume the coffee is in good condition and of passable quality, then a good yield will let that coffee taste as good as it can. Even in the 1950s they stated that extraction yield was not an indicator of coffee quality.

2. A refractometer can indicate that your burrs are worn in much the same way.

3. Inefficiency related to the basket will show up in the yield, diameter of the basket specifically may be less relevant than actual basket design.

4. Assuming the basket is appropriately dosed, with ideal head space, again anything that impedes extraction will show up, because that is what we are measuring...extraction.

5. Sure, a refractometer can't detect that...but then that's not it's job, it's job is to measure extraction, the barista's job is maintaining good practices...the refractometer is a tool, not a magic wand.

We keep referring to "refractometers", but this paradigm has been used since at least the 50's for coffee, more laborious oven dehydration and dessication was used, requiring larger samples of beverage and lab practices not so condusive to 'on the spot' measurement & real time results. VST coffee refractometers, are calibrated & guaranteed for accuracy...perhaps like a multimeter - if you want to measure a voltage or a current in a part of a circuit you don't look for a colour of a spark/ try and touch it/do a sensory evaluation ("this voltage here was found to be: Oooh tingly! Further up the rail it was more: Aaarghh! Turn it off! Turn it off!"), you measure it with the appropriate tool.

You sample espresso at 1minute after pulling the shot, ~4ml is then filtered & dropped into another vessel for cooling then 20seconds to stabilize in the refractometer, you can start drinking your shot and have your reading in 2minutes. There should still be significant volatiles in this time frame, you can sniff the shot all you want during this time & taste it after the sample is isolated. Extraction yield is the measurement of dissolved solids, not measurement of volatile aromatics which are not dissolved solids.

Yield analysis certainly helps, if you don't have a refractometer, brew by ratio & adjust grind to taste. Even the traditional Italian dialling in method aims to establish consistent extraction using everyday tools that are to hand, yield analysis just takes this a step further...both essentially have the same intent.

Making coffee, especially espresso, is very heavily driven by the use of tools (roasters, grinders, machines, PIDs, pumps, pressure profiling), just like those other tools a refractometer is just another one, but it's the only one that actually objectively evaluates the beverage you have made & the result of what you have done with those you used prior.


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## Neill (Jun 26, 2013)

All interesting reading. I certainly didn't mean to cause any controversy when I posted. Just genuinely interested in the general meanings of these terms, particularly in the modern setting where we can get a quantifiable figure so quickly.


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