What Is The Black Residue At The Bottom Of My Coffee?


What Is The Black Residue At The Bottom Of My Coffee header image

Do you keep getting that black dirt in the bottom of your coffee cup? You want to enjoy that last sip of brew but you can’t because it feels like you’re drinking wet sand. What is that and how can you fix it?

Residue at the bottom of a coffee cup is nearly always caused by coffee grounds that got through the filter. Good paper filters let no grounds through whatsoever. Metal filters almost always let some grounds through but this can be reduced by using a slightly coarser grind and filtering out fines.

If you grind your own coffee, a higher quality grinder will produce less fines and therefore less residue in your cup. The TimeMore C2 hand grinder offers a great grind quality with few fines for the money. Check it out on Amazon

What is causing the residue in your cup and what can you do to fix it? Keep reading to find out. There will be some more possible causes and solutions than described above.


What’s the black residue in your coffee cup?

First let’s see what that stuff actually is. It can be three different things;

  • Coffee grounds
  • Leftover residue in the cup/pot
  • Sediment from your machine

99% of the time you have something resembling sand in your coffee cup, it will be some of the coffee grounds.

Another simple reason can be that there was something in the cup or pot before you filled it with coffee. Sometimes things can fall in there and you don’t really see it. If you only get residue in your cup once, that might be the cause.

Coffee machines do get clogged with minerals from the water. Also, things like bacteria and mold can grow in a coffee maker if it’s not cleaned properly. How likely is it that those things come out of the machine and into your cup? Quite small. The likelihood that the residue is just coffee grounds is much, much larger.

If there is a nasty taste, don’t finish the cup. If what’s at the bottom just appears to be coffee grounds, you’re fine, it just doesn’t make for a very enjoyable cup if it’s too much.

Residue in a coffee cup.

Causes of grounds in your cup

Since most of the residue you’ll find in a coffee cup is going to be coffee grounds of some sorts, let’s focus on that. Residue in your pot, cup or machine from other sources should be easily fixed with a good cleaning.

Here are the biggest reasons;

Brewing method

First off you should take a look at how you brew coffee. The brewing method has a big impact on if/the amount of grounds that get into your cup.

In general; brewing methods that use a paper filter are the cleanest. Paper filters are the best at filtering out grounds out of your coffee. Paper filters don’t only filter grounds but also some other compounds like oils that are released from the beans. That creates a very clean cup of coffee. Usually, if you use paper filters to brew coffee, you won’t have any grounds in your cup. If you still do, look below for solutions.

Other brewing methods (pretty much everything that doesn’t use a paper filter), let through much more grounds.

So, if you’re using;

  • A French press
  • Moka pot
  • Phin
  • Other metal filters
  • Espresso machine
  • “Sock” filter

With those methods, you can always expect some residue to end up in your cup. That’s because the holes in a metal filter are too large to stop all the grounds

Grind size

That’s where grind size comes into play. Coffee beans can be ground into different sizes. You might notice that different bags of coffee have the powder that’s a different size. Some are finer than sand while some are a big larger.

Preground coffee is usually ground to a size that works well for most brewing methods. Some bags will have a (few) brewing methods indicated on them. A part of what decides the correct brewing method is the grind size. So if you’re getting a lot of grounds in your cup try buying a bag of coffee that’s more appropriate for the brewing method you’re using.

Many people buy ‘espresso’ powder because they want strong coffee. However, for anything except an espresso machine, that’s actually too fine. A bag that indicates it’s meant for filter coffee will be better.

For people that grind their own beans, try adjusting the grind size a bit coarser. Almost all grinders have a grind size adjustment.

Suggested post: What’s the right grind size for a moka pot?

Fines

When you grind coffee, not all parts will come out the same size. There will be the average size but also some particles that are larger but even worse, smaller. The smaller parts

If you buy pre ground coffee, the fines will be most concentrated in the bottom of the bag so you can try to avoid using the last bit. That’s a bit wasteful though. You can also try filtering the fines and use the normal sized leftovers. (see below)

For people that are grinding their own beans; the quality of the grinder will make a big impact on how much fines you get. Lower quality grinders will produce way more fines than higher quality grinders although it will always happen to some degree.

Brewing mistake

Maybe you’re using the right equipment and grind size but something went wrong in the brewing process. If it just happens once and the cups afterwards it’s fine, it’s going to be hard pinpointing what went wrong. During brewing there are some things you can keep in mind though;

  • Don’t overfill the filter: If the coffee gets out of the basket, it gets everywhere and your cup is just one of those places.
  • Be careful where you put the grounds: We all know powder can get into places it shouldn’t. Just make sure it’s all in the filter basket and nowhere else.
  • Make sure you assemble correctly: Some brewers like an espresso machine or moka pot have multiple parts. If they’re not put together right, water and grounds can leak past the filter.
Paper coffee filters
Paper filtered coffee usually has very little residue in the cup.

Solutions

Reading the causes of residue in your cup probably already to lead you to some solution that will work for you. However, maybe one of the solutions below will help you even further.

Clean

Obviously, keep your cups, pot and machine/filter as clean as possible. Make sure you didn’t accidentally spill any grounds somewhere they shouldn’t belong.

Cups and coffee pots should obviously be washed after every use. Coffee machines and some filters can need some deeper cleaning once in a while. Running the coffee machine with some vinegar or descaler will help.

also clean off any coffee grounds that aren’t in the filter. If they’re not in the filter, they can make their way into the cup pretty easily.

Double filter

If your current pot of coffee is just undrinkable because of all the residue, something you can do to save your pot is to just filter it through a paper filter (again). This will change the taste of the coffee a little bit but also get rid of any residue.

Don’t overfill

Some filters can quite easily be overfilled with water. Coffee grounds tend to float when they first get wet. So when you overfill the filter, the water takes the floating grounds with it around the filter. This allows the water and grounds to bypass the filter in some situations and get into the cup. It just creates a mess everywhere.

Of course try to prevent overfilling with grounds as well. Fresh coffee swells up when it first touches water. If the filter basket is too full, it will grow out of the basket and get everywhere. This is a real pain to clean up as well.

Buy different coffee

If you buy pre ground coffee, make sure you don’t get a bag that says “espresso”. That usually means the coffee is ground really fine. Get bags that are meant for filter coffee. (unless you’re using an espresso machine of course)

You can also try a lighter roast. The darker the bean is roasted, the dryer and more brittle it becomes. That means that darker roasts produce more fines when ground. With a lighter roasted coffee, this problem is a bit smaller.

Grinder

For people that grind their own beans, look into getting a better grinder. That’s an expensive upgrade for many people but it’s one that’s worth it. It doesn’t only reduce the residue in your cup but also the taste of your coffee.

If all the coffee particles are a similar size without big and small chunks, the extraction will be more even. Fines can give a bitterness to your brew. Getting rid of those will give you a better tasting cup.

A decent hand grinder can be bought for $30 and up. Those won’t be the most consistent though. A good hand grinder can cost $80 to $200. That’s not necessary for everyone but spending a little bit more than the minimum on a grinder is going to help.

For filter coffee, the TIMEMORE C2 is a great choice.

Electric grinders are much more expensive but a lot more convenient. Just a push of the button and you’ve got ground coffee. A hand grinder can require some effort.

Filter fines

There is a way to get rid of most of the fines. While getting different coffee or a better grinder will prevent the fines from being there in the first place, that’s not feasible for everyone.

There is a way to filter out the fines that are in the coffee grounds. Actually there are two ways;

Professional filter: There are filters which are specifically made for this purpose. They work very well but range from expensive to really expensive. They are basically sieves with different size holes. You pick the size hole you want to filter out and run the grounds through it.

Kruve makes a good filter that isn’t too expensive. There are lots of sizes to choose from all included in the kit so you have room to experiment. It’s a pretty compact package and is really nicely designed so it will look great in any kitchen.

It will also impress your friends while making coffee although you do run the risk of looking a bit snobbish.

Paper towels: The second, much cheaper, way is to use paper towels. Check out this post for a good explanation. Here are the cliff notes;

  • Get a paper towel. Large kitchen towels that are thick and have indentations work best.
    • Pour the grounds you need onto the towel.
    • Spread out the grounds on the towel so you’ve got a thin layer. Leave a little border on the towel so you can still hold it.
    • Grab the paper towel and pour grounds into a container
    • Repeat 3-5 times.
    • Start with about 20% more grounds than you actually need for your brew. After 3-5 times you’ll lose about 20% of weight.

A paper towel is cheap and almost everyone will have some in the kitchen. So this is a good way to try if the fines are really your problem. If it turns out it is, you know you should change your coffee or grinder.

Change your brewing method

If you’re using a brewing method that is more prone to letting grounds through, an easy fix is to change it. There are tons of

In some cases, you could add a paper filter although that would change the taste quite a lot to a point where you might just as well use a normal paper filtration method.

In general, paper filters clean all the grounds but also some of the oils out of the brew. This creates a very different taste than a metal filtration method which lets through more residue but also the oils. This means the two filtration methods have a very different end result in how the coffee tastes and feels.

So I can understand if you don’t want to change your brewing method because you like the taste of your coffee. In that case, try to reduce it as much as possible by using one of the methods named above.

A drip machine works to make paper filter coffee but if you want a nicer cup of coffee and don’t want to brew a liter at a time, check out a V60. It’s a pretty cheap and simple brewer that uses paper filters.

I’ve been using it for my morning coffee for a while now. And even when experimenting with grind sizes that are way too small, there has never been any residue in my cup.

Accept

To some degree, you’ll have to accept a little bit of residue if you want to use a brewing method that results in some residue. With the tactics above you likely reduce the residue to a reasonable level.

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