Under vs Over (extraction) - best explanations

[scottlucey]

Hey all,

I can admit that discussing under-extraction vs over-extraction has often gotten confusing.
This post is to seek out some of the best ways people explain these two occurrences.


Especially w/ espresso, I think ways in which this topic gets confusing is when people try to relate the extraction to 1) volume of coffee produced 2) shot time 3) colors 4) flavors.

Take it and run please.
Thank you.

sL

[James Hoffmann]

I'd broadly define underextraction as failing to get at least 18% of the solubles in the grounds down into the cup. With espresso you can do this most obviously by brewing too fast, or by pulling the shot too short. In the first case the lack of contact time doesn't yield sufficient extraction, with the second you have pushed sufficient water through to carry the solubles down into the cup.

Overextracion is the opposite - more than 22% (using the broad numbers here), and brewing too slow, or pushing too much water through the coffee.

[Dan Streetman]

I think James hit the nail on the head, although I usually explain it more simply than that (especially to beginners)

but under-extraction being too little flavor extracted, and
over-extraction being too much flavor being extracted from the coffee.

the challenge is, that especially in the espresso brewing process, both of these things can be happening at the same time. This is especially true when you have distribution problems, and/or un-level tamping.

more thoughts on this later.... (especially since I think this is research for an exciting project)!

[jason dominy]

I hate that this conversation didn't keep going. I personally would love to hear more about this subject. I didn't totally understand how coffee brewed could be under and overextracted at the same time until the other day in my manual brewing research. I brewed a cup using the Hario V60 that was thin (as in underextracted), but real thick and solid, (as a normal overextracted cup tastes like.) I then knew it, but couldn't wrap my head around how it happens, and what it exactly means. Can someone else shed some light on this?

[nick]

Not the best analogy, but can you cook a steak so that it's both 'under cooked' and 'over cooked?" Sure! Set your grill at 1000*F (if you could do such a thing) and burn the hell out of the outside, but leave the middle cold and raw.

It's helpful to do a quick inventory of the factors that each term (under and over) corresponds with:

Overextracted:
Grind too fine
Brew time too long
Turbulence too high
Temperature too high
Brew-ratio off (too much water to too-little coffee)

Underextracted:
Ground too coarse
Brew time too short
Uneven contact (i.e., a "dry patch" in the grounds that didn't brew)
Temperature too low
Brew-ratio off (too much coffee to too-little water)
Coffee too fresh
Coffee density too high (for those brewing parameters)

So simply put, can you have elements of the first list and the second list in the same brew?

[Andy Schecter]

I didn't totally understand how coffee brewed could be under and overextracted at the same time

Expanding a little on what Nick said:

1. If all the coffee grounds aren't wet right at the beginning of the brew time, some will have longer extraction time than others.
2. If the coffee bed is channeled as water percolates through, grounds in proximity to high water flow will be overextracted compared with grounds in proximity to low flow.
3. As Scott mentioned in his famous Chemex thread, grounds that are left high and dry on the filter will be underextracted compared to grounds near the bottom that are wet the longest.

These three issues may occur to a small extent on every extraction, but when they become severe, there can be noticeable under- and over-extraction in the same batch.

[jason dominy]

Great thoughts, and Nick you drive a good point. Andy, great words from you, as always. It's been great to delve further into this, and I've learned alot.

[KaralynnMcDermott]

Good thread on over and under extraction.
I agree uniformity of extraction is key, to avoid a brew that has in it both over and under extraction.

Some other culprits to add to the list:

Under extraction
Water that is heavy with mineral content (too much TDS)
Unlevel equipment so water flow is uneven
Clogged dispersion holes so bed of coffee isn't evenly saturated

Over extraction
Water that is pure (no mineral) content can be too aggressive

[jason dominy]

I will say that since getting the Extract MoJo kit and MoJoToGo, I've gotten a lot better at understanding my brews in terms of proper extractions.

[phaelon56]

For non-coffee people who will benefit from the simplest explanation I simply describe the result, then offer possible causes if their interest warrants further discussion.

Preface - "Coffee has a multitude of potential flavor components - some good and some bad"

Definitions -

Under-extraction: "Not enough of the desirable flavor components are extracted and the result is often weak, watery, and lacking in distinct character."

Over-extraction: "Too many of the bad components are extracted along with the good ones, but the bad outweigh the good, and the results is often bitter and has 'off' flavors."

For those who really do want to know more, I point out the inadequate water temps of typical home auto-drip coffee makers, the freshness/quality issue of the beans, the grind quality, and the importance of proper coffee/water ratio. Manual pour-over, a good bean supplier, and a good grinder (even if it must be a hand grinder to stay within budget) are the recommended solution.

When those suggestions are more than the conversant wants to deal with, I still suggest a good grinder and quality fresh whole beans. I suspect there's a sizable segment of the population that thinks they don't like coffee very much, or adds loads of sweetener and cream, only because they've never had good quality properly extracted coffee.