Why Your Coffee Grinder is Spoiling Your Coffee

Ground coffee: Is a bad coffee grinder spoiling your coffee

I am sure you remember your high school days with the different “cliques” or groups. Two of these stereotypical groups are the “jocks” and the “nerds”. Please allow a bit of this gross stereotyping for the sake of my analogy, to help me explain something about coffee grinders.

I can imagine that most jocks spend their free time pumping dumbbells in the gym, while the average nerd tinkers with a computer or argues about the merits of Star Wars compared to Star Trek. Naturally, this leads to a single jock weighing more than all the school’s nerds combined, and also being better at physical sports like rugby;  while the nerds excel in more intellectual pursuits like chess.

Now imagine, in the interest of equality and political correctness, the school introduces a new selection policy for both the chess team and the rugby team. Under this policy, there must be learners of all physiques in the rugby team and learners of all levels of intelligence in the chess team.

The result? Both chess and rugby might suddenly become way more entertaining for the spectators, but of course, the performance of both these teams would be ruined by such a policy.

Now, what on earth does this have to do with coffee grinders?

Most coffee grinders on the South African market can be better described as rebranded spice grinders. Such a grinder, or rather a chopper, has a rapidly spinning blade breaking up the beans into bits of all sizes. This type of grinder is your politically correct selection policy for grind size. It makes sure there is everything from fine powder to big chunks or even whole beans in the same grind.

The result is bad coffee, just like our equal-opportunity sports teams above would result in bad performance.

Blade coffee grinder.

A blade type coffee grinder or, more accurately, a spice chopper.

But why? The next two sections should clear this up. First a bit of technical background… (before getting back to nerds outsmarting jocks, or getting beaten up by them):

Nerding out on coffee extraction

A coffee bean contains about 30% extractable substances. But, unfortunately, not all of it is good stuff. Some of it is nasty and bitter.  Thankfully the nasty stuff extracts more slowly into the hot water when brewing coffee than the delightful, aromatic, good stuff. The ideal percentage of brewed solids to extract from the coffee bean is 18-22%. If you extract more (over-extract) you get a bitter cup. If you extract less (under-extract) your coffee will taste sour, which is also undesirable. This is because the acidity of the coffee comes out first, and needs to be balanced by the sweetness and other flavours still to be extracted.

Now, what does this have to do with ground particle size? Science and common sense tell us that it is much quicker to extract substances from small particles than big ones. The surface area of thousands of small particles in contact with the water is exponentially greater than the surface area of a few big chunks.

So that is why one generally uses a fine grind for espresso, which only exposes the ground coffee to hot water for less than half a minute, and a much coarser grind for, say, a plunger which exposes the grounds to hot water for much longer (+- 4 minutes).

Maybe you can already start to see why a mixture of fine and coarsely ground coffee would be a bad idea. But let's return to the jocks and nerds to help us understand:

“Don’t let the nerds play ball with the jocks!” or, “The importance of grind uniformity.”

On the rugby field, it does not take long for the puny nerds mixed among the jocks to get beaten to a pulp and, literally, be “extracted” to tears. We could say the nerds have been over-extracted. On the other hand, the jocks in the chess tournament have too little time to “extract” a smart chess move from their untrained minds. We could say the jocks have been under-extracted.

So, do you get the point of my analogy? If you have a mixture of finely and coarsely ground coffee it will be very difficult to extract an excellent, balanced cup of coffee. Worst case scenario - bitterness will already be extracted from the fine powder, making your cup bitter (called over-extraction, remember), while much of the good balancing flavours are still locked away in the big chunks (called under-extraction). So your cup can be both bitter and sour at the same time.

But how can you fix this?

 “Use the best man for the team!” or, “Check your coffee grinder.”

The better your grinder is at producing a uniform grind – the better your chances of brewing a good cup of coffee. The better the team, the better the chances to succeed – as simple as that!

As mentioned the “spice grinder” kind of coffee grinders are the worst, while flat burr and conical burr grinders fare far better. Spice grinders are some of the most economical options available, but you can also find really affordable hand conical burr grinders (similar to a pepper grinder) locally, e.g. those made by Hario.

Pause Coffee Roastery understands the importance of a good grind as one of the steps in pursuing the perfect cup of coffee, which is why they use of one of the most advanced coffee grinders on the market, the German made Mahlkönig EK43.

Where possible, it is desirable to grind your coffee just before brewing it. However, if you don’t have a grinder at home yet, or you decided to reserve your spice chopper for, well, spices, we suggest buying ground coffee that is as fresh as possible, i.e. fresh coffee in small batches. Click here for an excellent article comparing coffee pre-ground in a Mahlkönig EK43 with coffee ground at home in various coffee grinders.

One way Pause Coffee Roastery tries to make it as easy as possible for you to always have a supply of fresh coffee on hand, is their fresh coffee subscription service (25% off for the 1st month!), no matter where in the country you are -  just click here. Remember, you can also choose your grind size when choosing ground coffee, based on the brewing method you use. 

And relax, whether you were a jock or a nerd. Coffee doesn’t discriminate.

 

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