In his introductory article in his new column on CoffeeGeek, Chris Weaver, a Head Barista at a popular cafe in London walks us through the process of dialling a grinder and making good espresso better.
Posted Thu Mar 1, 2012, 3:19am Subject: Re: Grinder Adjustments 101 by Chris Weaver
Good article with practical and solid real life information.
Two things caught my eyes.
"If you notice a lot of sourness in your shot (think lemons) or the espresso is really thin with zero mouth-feel, then there's a good chance it's under-extracted. This can be caused by the shot running too fast or the yield being too high."
The under-extraction is connected to low yields. ie. Too little is extracted from the ground coffee ->under-extraction-> low yield.
"a thick pour with a lot of bitterness, chances are you're over-extracting the espresso and pulling in a load of undesirable solubles. This is normally caused by the shot running too slow with the yield being too low in that time."
The over-extraction is connected to high yields. ie. Too much is extracted from the ground coffee -> over-extraction -> high yield. If the flow is slow, it might also be connected to under-extraction where the espresso is strong but underdeveloped.
Posted Mon Mar 5, 2012, 5:57am Subject: Re: Grinder Adjustments 101 by Chris Weaver
@thecatinside; Under-extraction means that the coffee grind is not yielding what it should (in terms of solubles) usually due to the fast passage of water through the grinded beans. Thus under-extraction relates to high volume of watery or sour yield (and over-extraction to low volume of overly strong or bitter extract ). Thanks for a great article Chris!
Posted Mon Mar 5, 2012, 1:41pm Subject: Re: Grinder Adjustments 101 by Chris Weaver
georgie Said:
@thecatinside; Under-extraction means that the coffee grind is not yielding what it should (in terms of solubles) usually due to the fast passage of water through the grinded beans.
That is another way of saying what I said about under-extraction. In the original article there was a mix-up with terms "high yield" and "low yield" which I was trying to point out. Low yield and therefore under-extraction too, might indeed be a result of "fast passage" which might be a result of too little resistance from the ground coffee.
georgie Said:
over-extraction to low volume of overly strong or bitter extract
Strength of coffee is not relevant to the yield. It is as possible to have weak or strong coffee which was still under- or overextracted. Strength is the amount of dissolved solids divided with the water (solvent).
chrisweaver87 Senior Member Joined: 11 Sep 2008 Posts: 5 Location: London, UK Expertise: Pro Barista
Posted Tue Mar 13, 2012, 8:52am Subject: Re: Grinder Adjustments 101 by Chris Weaver
Hey guys. Thanks for the heads up. I did notice these errors as soon as the article went up, managed to get my head all confused whilst writing it. Going to get some revisions done on this.
Posted Thu Mar 15, 2012, 9:02am Subject: Re: Grinder Adjustments 101 by Chris Weaver
I'm embarrassed for all the nitpicking but since I've started might as well go all the way.
"Often light tamps can result in a higher likelihood of channelling as well as poor distribution before tamping."
Although tamp needs to have some "oomph" in it, it's a pity if people interpret this so that light tamping was ultimately a bad thing. In commercial settings tamping light is the only way to have a career free of tendonitis and other problems. I personally have learnt this the hard way. Besides it's faster and somehow easier to tamp straight with light tamp and loose wrist.
Distributing and tamping are two different things. If tamping is adjusted to match the lacks in distribution, there's a problem. In my opinion distribution starts from dosing the coffee evenly to the filter and ends when the tamper is touching the grinds.
"This is normally caused by a high yield in a normal shot time, or a regular yield with an excessively long shot time." Over-extraction with regular yield is a paradox.
chrisweaver87 Senior Member Joined: 11 Sep 2008 Posts: 5 Location: London, UK Expertise: Pro Barista
Posted Sun Mar 18, 2012, 4:43pm Subject: Re: Grinder Adjustments 101 by Chris Weaver
When I refer to the espresso yield, I purely mean the weight of the espresso as a means to express volume. I don't understand why this would be a paradox?
Regarding tamping, it's been one those interesting topics of debate in the industry for a long while. To clarify, when I say a hard tamp, I don't mean tamping so excessively that, as you mention, it would bring Tendonitis and other issues into play. I simply mean a tamp around the 30lbs of pressure mark that is recognised as an industry standard. I have been using this tamp for many years now in high-volume bars with absolutely no issues in my wrist. Technique is definitely key here.
As you say yourself, when I refer to light tamp, I mean one without "oomph". I have observed throughout a huge amount of shots that, regardless of correct distribution, a light tamp still results in much more channelling, primarily around the outside of the basket.
I would guess that this is caused by the tamp being inadequate to properly create a seal around the outside of the puck.
Thanks so much for your feedback, it's great to have ones theories so close scrutinised!
Posted Sun Mar 18, 2012, 8:55pm Subject: Re: Grinder Adjustments 101 by Chris Weaver
I hope you don't mind another comment, this time from the other side of the pond.
Brew temperature and grind size are primary determinants of extraction (and hence espresso flavor profile). Your discussion focuses on channeling (for sourness) and overextraction (for bitterness). I have found that grinding finer and increasing the brew temperature are generally effective in reducing sour flavors in espresso. Similarly, grinding coarser and lowering the brew temperature work well to reduce bitterness. (Obviously, if you make any significant changes to grind size, the dose must be adjusted to keep the flow rate within reasonable limits.)
Re channeling: it is pointless to play around with grind, dose and brew temperature if you have not mastered the mechanics of making espresso. When there is channeling - which is best diagnosed using a bottomless portafilter, not from spent puck postmortems - it must be corrected before you can proceed further.
Overall a good article. It's nice to see a professional barista endorse the digital scale as a valuable tool for dose consistency and monitoring extraction ratio.
chrisweaver87 Senior Member Joined: 11 Sep 2008 Posts: 5 Location: London, UK Expertise: Pro Barista
Posted Mon Mar 19, 2012, 9:17am Subject: Re: Grinder Adjustments 101 by Chris Weaver
To be honest, brew temperature is something I chose to not mention particularly in the article, but yes you're right, low temperature can under-extract a coffee resulting in sour and vice-versa.
I didn't for it to be about chanelling primarily as the cause of sourness though this of course can result in that. I think the major causes of sourness, aside from temperature as you mention, is under-extraction through too fast a water passage or a shot which is pulled to short.
I agree entirely with the mechanics of pulling shots, however I wanted this article to be a step slightly higher than that, I feel there is much more literature online regarding the technique of pulling shots as opposed to actually understanding how to recognise and solve extraction issues.
And yes, I live and die by the scales (and of course my tastebuds). Easily one of the most important tools in a coffee bar.
Posted Mon Mar 19, 2012, 2:06pm Subject: Re: Grinder Adjustments 101 by Chris Weaver
chrisweaver87 Said:
When I refer to the espresso yield, I purely mean the weight of the espresso as a means to express volume. I don't understand why this would be a paradox?
My bad, I didn't pay enough attention when eyeing trough the revised version. I associated yield with "extraction yield" instead of the mass.
But even if the yield is understood as a mass of final product (the espresso that is), then there's still some refinements to be made with these propositions
This (under-extraction) can be caused by the shot running too fast
and
This (over-extraction) is normally caused by a high yield in a normal shot time
They are essentially describing identical occurrences which leads to the nasty and unfortunate situation of under- and over-extraction being identical as well.
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