Underextraction/Overextraction: Espresso

Wednesday January 17, 2018

Distiguishing the two terms "over-extraction" and "under-extraction" have always been two things that I found to be slightly confusing.  In espresso terminology, under-extraction is the idea that the coffee particles are too coarse and the water doesn't have a chance to grab everything or as much as desired and fully extract the shot.  This creates a sour/unpleasant and acidic result. Under-extraction can also be a ratio that is not quite enough in the end result or yield, which means you are not getting enough of the coffee extracted resulting in a short and muted shot with very little complexity.  The other component to look at is the brew temperature, because if the brew temp is too low the coffee will be thin, and sharp.  These are the common areas that I face when dialing in coffee at work.  I believe that over-extraction in espresso is something that I don't deal with as much, unless the grind is really off or the brew temperature is way too high.  I am not saying that over-extraction doesn't exist, but I do believe that in my situation recently I have been confusing the two and have had to revisit some basics to get myself on the right track.  So here are the corrections I have been making and the results to go along with them.

Most of the time, taste flaws are directly correlated with the grind setting.  When the espresso has that sour taste with very little sweetness I usually draw out a little bit more of a yield to lengthen the shot which will give a little more complexity and extract more chocolate, vanilla and those sort of flavors.  If it is still not quite there, I will tighten (make finer) the grind until that sourness/under-extracted quality is eliminated.  As I tighten the grind I just barely ease up on my tamp so as not to create this impenetrable puck, because the particles are smaller it is important to do so.  I can usually get right in the zone there, but when you extend the yield of the shot the strength will decrease.  Extraction increases but the body of the shot can become thinner and more watery.  This is not a bad thing but in my case I want to optimize the sweetness, the viscosity, and the complexity.  That is where our espresso at Vertigo is at its best.  

This is where Brew Temp comes in.  I will keep all the numbers that I have locked in, but sometimes taste this weak/acidic flavor that I can't get rid of.  Since the dose, yield, and time are all in place I will then increase the brew temp up just half a degree and go from there.  By doing this it thickens up the shot and cuts through that acidic bite that it has, but by also doing this you are gaining back this "heavier taste" that wasn't there before.  Be careful not to take the temperature too high, because that will scald the espresso.  

These are just the small details that I have been dealing with recently and hopefully have shared some answers to questions some of you have, and if not I hope you enjoyed the nerdy of this one.



Take Care everybody! Below I attached Matt Perger's guide to the dial-in method