Why is My Coffee Soapy?

A soapy taste in coffee is the mark of one of two things. Either:

(A) there is soap in your coffee! or....

(B) your coffee is underextracted.

Now the first suggestion that there may be soap in your coffee is not altogether tongue-in-cheek. There very may well be. If you think you taste something funky in your coffee, you should always check for foreign agents first: is the brewer fully cleaned, rinsed out and seasoned with coffee? What about your cup? When is the last time you took a look at the interior of your grinder hopper? (This may not seem like a likely source of soapy tastes in a coffee shop, but many home brewers keep grinders on countertops where they can get all kinds of other food or cleaning products in them.) So, first make sure the soapy taste isn't actually soap.

Because if it's not, you have a different problem entirely. One that's just about as common as a bar of Ivory soap. Soapy tastes in coffee are a mark of underextraction.

Remember: underextraction is not the same thing as weak flavor. A coffee can be full strength or even extra-strong and still be underextracted. And it could be overextracted and yet still weak (that's way too common for me to even think about right now without getting grumpy.)

Underextraction refers to what percentage of the solubles in the ground coffee are ending up in your brew. Each compound in a coffee bean — and there are hundreds — has a different flavor. Since the different compounds extract (that is, dissolve into the brew) at different rates, that means that a coffee extracted quickly will taste differently than one that takes a long time.

If I extract just 1% of a hundred coffee beans, I will have a full bean's worth of solubles, but they will be all the same boring flavor from that first moment of extraction. If I could somehow extract 100% of one coffee bean (not technically possible, but play along), I would have the same amount of solubles, but a much more overextracted, bitter taste. In fact, it would taste like chewing on a coffee bean. The fact that chewing on a bean is generally not as pleasant as drinking a well-extracted cup of coffee shows us just how important a proper rate of extraction is. If it weren't important, we would all just eat coffee instead of drink it.

There are devices that measure extraction, the most interesting of which is the Extract MoJo. I recommend at least learning about this topic if you are a professional. But the best tool — for professional and enthusiasts alike — is always your tongue. Remember Daniel's mantra: Coffee should taste GOOD!

The ideal rate of extraction is right around 20% of each bean. Keep in mind this has nothing to do with strength! Only flavor. If you want stronger coffee, you should just get 20% from more beans... not go for a higher percentage. If you want weaker coffee, back off of the amount of coffee, but leave it at a 20% extraction rate.

Practically speaking, getting back to soapy coffee, if your coffee tastes soapy, the water needs to spend more time with the coffee, or the water needs to be hotter, or both. If you run water through coarsely-ground coffee in under 1 minute, for example, you will have underextracted, soapy coffee. Pour the water more slowly, or make the grind finer so the water has to work more slowly through the slurry. There are also, of course, other factors (like water composition, and many others) that can affect extraction rate.

Some other words people associate with the taste of underextracted coffees are sour, minerally, metallic. To me, it sometimes tastes like a piece of aluminum. This is all on my mind because yesterday I poured myself a Chemex a little too eagerly and a Kenyan coffee that has been kind to me all week suddenly tasted flat, soapy, and just plain bad.

Remember kids, Don't Do What "Danny Don't" Does. Make your coffee right. Leave the soap in the soapdish, and the coffee in the pot.

Comments

[mike P]

forgive me if what follows is not as well formed of a thought as it should be but your touching on somehting I have been thinking about for a bit... You mention that compounds in coffee extract at different rates making coffee that is brewed quickly taste different from coffee that has an extraction time stretched longer. then after that you mention that golden rule of 20% that people have been speaking about lately. does this imply that you can potentially get 20% extracted from the same amount of beans using multiple times/grind settings that will all taste differeent? If so then which 20% is the magic one? Am I way off base on this?

[Daniel Humphries]

Mike:

I've wondered about that too. My speculation — and my anecdotal experience — suggests that, no, not really. You can't get different 20%'s (percentseses?) that all taste different out of one coffee. Maybe there's some difference at the margins. I think that with radical differences in temperature, you sometime get surprisingly different tastes from an espresso that aren't necessarily "classically" under- or over-extracted tasting. Maybe those are instances of taking out different proportions of different solubles while still taking out the same overall amount of solubles.

However, I'd be surprised if this is anything other than a marginal phenomenon. Caffeine, for example, dissolves almost instantly in water. I don't think that changing grind size or temperature or dwell time or pressure or anything else is going to change that, and I suspect most of the compounds have similar "set extractions."

But I haven't seen data one way or the other. What you need is a spectrometer and the ability to do trace analysis, and then a team of expert cuppers to cup blind several times to see if there is (a) any difference in which 20% is coming out and (b) if it actually makes a tasteable difference or if this is all just wasteful nerdery. Sounds like a vacation to me, actually!

But this is the kind of thing you are talking about, right?

[joe hoppy]

I went to ZtarBucks in Plano Texas on Legacy Dr. and my coffee is very soapy looking for over 5 minutes?? WTF? is that normal??

[Daniel Humphries]

Joe:

I can't picture exactly what you are talking about, but if you are talking about an oily-looking sheen on the surface of the liquid, in a cup of black coffee, those are oils that naturally occur in the coffee bean. The darker a coffee is roasted, and sometimes also the staler it is, the more visible the oils will be. Maybe it was that.

[Michael]

I know I'm a bit late commenting on this post, but it was mentioned that to help get a higher extraction rate "the water needs to spend more time with the coffee". So, for someone brewing at home, would using two filters help? Or am I off base with that one?

This was exactly the post that I was looking for, thank you.

[Daniel Humphries]

Michael: First try increasing the water temperature. Then try using more finely-ground coffee. Using a double filter isn't really a good long-term solution as it doesn't address the root of the problem.

If you have an automatic machine that doesn't let you control the water temperature, considering upgrading (for much less money!) and getting a hand pour-over system. If you are using pre-ground coffee, invest in a nice burr grinder. You won't regret it!