Overextraction.... um... what is it?

[meg-e]

Im still on my first star so Im forgiving myself for asking what might APPEAR to be a silly question...   :-[

Im confused as to exactly what overextraction is/means. I know it has something to do with time (30sec?) and volume (30mls?) but people seem to use the term with careless abandon (Im being dramatic I know) and now Im confused.

I dont know whether its too much water through the coffee, water taking too long to get through the coffee or something else like just weak coffee? :-/

So once Ive worked out the exact definition (yes Ive done a search)... what are the variables that might cause it (I need lists peoples)? And why might these variables cause it.

Also, is it all the same for a double shot - just double?

hmm, I think thats it. thanks in advance!

If there is a thread out there that deals with this Id love to read it. I couldnt find it though.

Cheers

Meg


p.s. I couldnt work out what topic this question should go under sorry if its in the wrong place.

[JavaB]

Re: Overextraction.... um... what is it?

meg-e

Not a silly question at all (IMHO the only silly question is one which is not asked! )

This is actually a difficult question to answer.... but Ill have a go..

Over extraction occurs when the flavours, coffee oils, and other "good bits" which we want have been removed from the coffee grounds.... you then get bitter, unpleasant tasting liquid going into your espresso which spoils the flavour and texture.

The first thing to realise is water is lazy - it always takes the shortest path through the coffee puck..... so if the grind isnt evenly tamped (not flat or not tamped at the edges properly - thats where the water will go - and pretty quickly remove the wanted bits in those relatively small areas.... so you rapidly over extract the grounds in those areas..... (and extract nothing from the rest of the puck)...

If the coffee grinds are too coarse.... you extract the wanted bits from the outer layers of each bit of coffee.... and nothing from the inside - again the coffee is over extracted quite quickly....

If you have a deeper basket- therefore more coffee grounds- you can extract more before you start to extract only the nasty stuff.

If you want a flat black.....and you have tamped correctly and the grind is the correct size.... but you continue to pass water through the puck... you will get coffee which is over extracted...

So what has all this to do with 30ml in 30 seconds (some say 25 seconds)?

Well, assuming the coffee is the correct grind size, and you are tamping correctly (flat top on the puck, tamped right to the edge with 13.5 Kg of force).... you should get 30ml of beautiful tasting espresso in 30 seconds from a single basket or 60ml in the same time from a double...... and that is what you aim for.....

However there is a tell tale sign of overextraction..... instead of the nice dark crema you will get when the bits you want are being extracted, it will turn light in colour - usually referred to as "blonding" - at that point stop the extraction or you will get the bitter unwanted flavours....

Blonding might occur at 20ml.... (too early- but stop the extraction anyhow)... most of the flavour you want is in the first and second third of the extraction - you will still make a vey nice coffee- but it wont be quite as strong.

If you keep going - you will get over extraction - and nasty tastes....

Always aim for the 30ml in 30 seconds.... but as soon as you get blonding - stop the flow and you will avoid over extraction....

If it comes out blond almost from the start.... you havent got even water flow (tamping problem) or the grind is too coarse - and you will be over extracting straight away...

I hope that isnt as "clear as mud"....

EDIT: I forgot there is another type of over extraction (just in case I havent confused you too much already)

If the water passing through the coffee is too hot (not normally a problem) it also extracts too much of the bitter, unpleasant coffee oils which normally are extracted after the ones you want in your espresso.... its sort of normal extraction and over extraction occurring at the same time :.

[moso]

Re: Overextraction.... um... what is it?

Recently I tried pouring off the first half of a mocha-pot brew, then letting the rest gurgle though in the normal way. The first half was nice, a superior brew. The second half was truly foul. It tasted downright unhealthy. Thats one way to get an idea of over-extraction. (The thought that most people with mocha-pots drink the entire through-put is a bit disturbing).

[rgow6208]

Re: Overextraction.... um... what is it?

Ok, before this thread gets overextracted, heres my 2 cents worth, as I understand it:

To put it simply:

1. Overextraction: When the grind is too fine or tamped too hard, the coffee takes longer to come through the puck and when it does come out it drips from the portafilter (PF), rather than flowing in the shape of a mouses tail, and is black in colour. Taste is bitter.

2. Underextraction: When the grind is too course or tamped too light, the coffee comes through the puck too quickly and gushes out of PF. Is light or blonde in colour. Taste is weak.

So the variables are, primarily:
A) Grind
B) Tamping pressure

A double shot is usually one shot pulled and then another separate shot pulled and added to the first. So, if the first shot is good and both shots are done the same, there should be no diff to doing a double shot to doing a single. But it would of course be possible to pull the first shot
correctly, tamp too hard on the second shot and get the second shot overextracted. Or tamp too lightly and get it underextracted.

The alternative to a double shot is what some people call a "strong" coffee. Which usually means they just let the pour go a bit longer on a standard shot. I find this a poor substitute for a double shot!
You can also have a Ristretto -- just the first half of the pour -- by stopping a normal shot early. Dont go the full 30mls in 25 secs, stop at about 15mls in 15 secs. This also gives a fairly strong coffee because it contains higher concentrations of the coffee oils in the liquid. (The longer the pour, the weaker the pour gets). A double ristretto is another strong coffee choice and is the same as a double shot (ie, two separate shots pulled and then combined in the one glass), but with 15 sec pours instead of 25 sec pours.

Hope that confuses matters up!

[JavaB]

Re: Overextraction.... um... what is it?

meg-e

Now I said it wasnt easy..... you now have two different views....

To add to your confusion.... Ristretto is italian for restricted.... the other way of making a ristretto is to reduce the grind size.... and so reducing (restricting) the amount of water which can flow through the puck..

The grind is chosen so that you get 15 ml in 30 seconds (single basket) or 30ml in 30 seconds (double basket) the resultant coffees being a single ristretto and a double ristretto respectively.

Both methods are used..... ( half time pour and finer grind pour) but the flavour produced is different in each case - the half time pour is easier for the barrista (he/she doesnt have to alter the grinder!!)

Now you are really confused :-/

[marcstolk]

Re: Overextraction.... um... what is it?

meg-e


If it comes out blond almost from the start.... you havent got even water flow (tamping problem) or the grind is too coarse -

I would have considered this as "Under extracted" ??

Where as when blonding occurs after the initial 30mil/\/30sec has passed then yes, over extraction... If it happs earlier, then some adjusting of the grind a tab finer OR - updose more...(this would depend of you have a nice puck or not)

Marc

[marcstolk]

Re: Overextraction.... um... what is it?

Now, you can pull a "tighter" espresso pour using something like "25mil in 40sec" then Id refer that as a ristretto... anything tighter you may have a "over" extracted and youll get bitter espresso....

This is a very good discussion - thanks for asking the question Meg-e ... (Im sounding like a politician answering a question from his fellow party member - I thank the honourable member for there question... etc etc)

Further to this, every espresso machine is different... some updose well, some dont etc etc...

Marc

[marcstolk]

Re: Overextraction.... um... what is it?

JavaB - you beat me to the ristretto part

Marc

[JavaB]

Re: Overextraction.... um... what is it?

meg-e


If it comes out blond almost from the start.... you havent got even water flow (tamping problem) or the grind is too coarse -

I would have considered this as "Under extracted" ??

Marc

Marc...

Yep it is a very interesting question from Meg (and sure isnt easy to answer)

I guess it depends whether we are looking at the product (whats in the cup) or whats left in the coffee puck..... a fast pour is taking the oils etc from the surface of the coffee grounds..... and pretty soon it has removed the wanted ones and then the bitter oils start to appear in the cup (over extracted)....

but most of the good oils remain in the coffee grounds in the basket - they have been under extracted......

Kind of a glass half empty / glass half full discussion ;D

[marcstolk]

Re: Overextraction.... um... what is it?

So true JavaB.. so true....

[rgow6208]

Re: Overextraction.... um... what is it?

Ok, I got caught out.   Trying to dish out knowledge i didnt have  :. Stuffed up the ristretto thing  :P.

Youre right, you adjust the grind or the tamping so the flow is restricted and you only get 15ml in 20-25 secs (not 15 secs, as i was thinking).

I stand by what i said about overextraction. But you are right also. Its all to do with how much of the oils are extracted by the flow of hot water. Too fine a grind or too heavy tamping will choke the flow and cause it to leech too much of the oils out of the grounds by the time it gets through the puck. Overextracted and bitter. So in this scenario, overextraction is in process even before the coffee starts to drip out of the PF.
But I can now see what you were saying, JavaB, about the extra-long pour also leading to overextraction. I wonder, is it due to different oils (more bitter in taste) being extracted, or a difference in surface oil and oil deep within the grounds (if there can be deep within a coffee ground!) or a difference in what happens to the flavour of the oil if exposed to boiling hot water for too long (gets burned)?
Likewise, in my scenario above, do you agree that it leeches too much of the oils or do you think it is that the oils get burned by the hot water not flowing and thereby spending more time (and presumably applying more heat) to the puck and its trapped oils?

[niallpedlow]

Re: Overextraction.... um... what is it?

This is the way I look at it, and I may be wrong, but this is the way my logical brain works:

The over / under extraction refers to the coffee grounds left in the basket, after the shot has been poured.

If the coffee grounds have "good bits" (Ill leave the pros to define the good bits) left in them, then they are underextracted.  If the coffee grounds have all the "good bits" extracted, plus some of the "not so good bits", then the coffee is over-extracted. Then theres the bit in the middle of the two extremes where the coffee is good.

My brain is also a tad scientific, and I have found a few articles over time that explain what actually gives coffee its taste:

http://cosmicvariance.com/2006/08/07...ence-of-coffee
http://www.coffeeresearch.org/science/aromamain.htm
http://www.coffeeresearch.org/science/bittermain.htm

It may or may not help you to make a better coffee, but it sure is some interesting reading, and puts a bit of scientific explanation around extraction.

[nunu]

Re: Overextraction.... um... what is it?

I like the non-scientific version better. Over-extracted = crap, under-extracted = crap.

You can over-extract a shot and still have the required volume. Same with under-extraction. Brew temperature in this case is the culprit. Bitter shot vs. sour shot.

[JavaB]

Re: Overextraction.... um... what is it?

I like the non-scientific version better. Over-extracted = crap, under-extracted = crap.

;D ;D ;D ;D

nunu...

Ive got to agree with that statement..... if all the good bits are in the cup and the bad bits are in the puck - we have correct extraction...... the rest is down to semantics... but you have defined it very accurately as cf@p coffee!!!

Now onto the meaning of life?- easy answer- to get the least cr@p during whatever time we have ;D ;D ;D

[meg-e]

Re: Overextraction.... um... what is it?

Gawd!

Thank you so much for spending so much time answering this! Im sure you had other things to do - I appreciate it!  

And I guess Im glad I asked! :-/
Ill need to read it all through a few times but Im sure Ill get there. Im using a presso and its all a bit manual and inconsistent at the moment so Im looking to narrow down the variables. I suspect grind size might be my issue but Id rather work through it systematically.

Thanks again, I hope this has also helped anyone else who was wondering the same thing.

Meg