Fine vs Coarse! Dialing in your filter method.

What is the 'correct' grind for brewing filter coffee, whether it's Syphon, Pour Over or AeroPress? This has been a hot topic ever since the 'Third Wave' coffee scene took off a couple years ago.

Some baristas say, that the grind has to been slightly on the coarser side, because we are not dealing with pressurized water. Some say the grind has to be finer, so the water and coffee have enough time to interact with one another.

In this little experiment, I look at both sides of the argument, and try to come up with a rational answer.

Firstly, we need to decide on what type of water we are going to use to brew our coffee. This subject is commonly overlooked in the cafe environment, as most people just take the hot water out of the espresso machine, as it is convenient and it is at the correct temperature. But to a get 'true' reading of the coffee, we should not be using water that has been purified through a filtering device, as most of the natural minerals have been striped away, leaving us with a slight metallic taste. Also, we don't know what state the machines water boiler is at, as it may have scaling, which effects the taste in the cup.

So as a general rule, we should be using bottled mineral/artisan water, something that has a low 'total dissolvable solids' (TDS).

Obtaining good quality mineral water is no means a difficult task. Your local supermarket should have a sufficient selection to choose from. In most case scenarios, soft water is the best, something that has a TDS of 120-150 and a pH level of 7.

Antipodes and Otakiri water are two brands I highly recommend. Both are from the same source (Whakatane, Bay of Plenty), and both are in glass bottle form. Plastic tends to affect the taste. The only down side, is that they are quite pricey at $5.50 a bottle.

So for the purpose of this experiment, I went for cheaper water, Waiwera Artesian water. Now, this water does not produce a sweet a cup as Antipodes or Otakiri, but it is still better than general tap water.





Secondly, the grinder, I recommend using one that has ‘stepped’ gauges. Having one with this feature is beneficial for recording the grind settings. The Malkonig Vario W is a little domestic grinder I own, and used for the Brewers Championships. Its extremely accurate and well worth investing into.

So, getting back to the purpose of this exercise, I made four Aero Press coffees, all with slightly different grind particles. Two of them are made from fine grinds and the other two are from coarse grinds. All four coffees were made with the same coffee to water ratio, fourteen grams to two hundred mls of water and brewed at the same temperature.


In the first test, The AeroPress on the left, had a coffee grind setting of 2a and the AeroPress on the right had a grind setting of 8a. Water was brewed to ninety six degrees.


There are two styles of brewing AeroPress coffee, traditional; where the AeroPress is already setup on top of the drinking vessel, as you pour and let it steep, the coffee is already starting to bleed from the filter base into the cup, I found this method to be very inconsistent and plain sloppy.

The other technique is the more commonly used one, and by far, it is the more creative. This technique is known as the inverted method, it is when the AeroPress is setup, upside down, and then flipped on its head, when it is time to brew the coffee

The technique I used is based on the Koppi Coffee Roasters style. Some brewers remove the coffee slurry after its steeping time, believing it helps with the clarity of the cup, but after a few trials with this method, there is not much of a difference, and is not 100 percent plausible, as some grinds are heavier than others, and tend to sink to the base of the filter. Scandinavian roasts are extremely light which equates to the grinds sinking to the bottom.


Remembering that the coffee on the left was brewed with a finer grind setting 2a.
Taking a sample of the cup, I placed a few drips in to the sight well of the refractometer.

The findings of this cup, translate to be something of an over extracted, borderline bitter type beverage. It predominately had a multi/grainy type mouth feel.

The cup on the right has a 'french press' type grind setting 8a. Again, taking a sample of this and placing it into the refractometers sight well.


As you can see from the above diagram, the grind setting falls out of the 'ideal' taste window. It is telling me that the water has not had enough contact time with the grinds to properly fuse together, otherwise commonly known as underdeveloped, but just to tickle my curiosity, I wanted to give it a try.

Confirming what technology has told me, this cup was, indeed very weak. It tasted diluted and sappy, if almost felt like something had been removed from the coffee.

Now, taking from what I learnt from the last test, I decided to tweak my grind settings. 



Cup left deals with a slightly coarser grind 3a and cup right has a slightly finer grind. Hoping that one of these settings will give me the right 'Grind' for my Aero Press. Visually there is not much of tactile difference between the setting 2a compared to 3a, but I was on a hunch, that the slight change  in the grind will result in a more pleasant cup.

As you can see from the result, the TDS reading is above the underdeveloped line and sitting in the middle of the ideal taste window, so science wise,  this is a balanced, well brewed cup of coffee.

Now for the right cup.


Even though, i've made the grind slightly finer with a setting of 7a, the right AeroPress still falls outside the 'ideal' window, with it just sitting below the 'underdeveloped' line, but I thought it was worth tasting, since it was just slightly off. Unsurprisingly the cup was not that bad, maybe lacking a little in the mouth feel department, but it had a nice balance of sweetness and acidity.



It is tough to give a logical black and white answer between the two settings, coffee is a volatile product and the roast profile, type of bean or origin play a big factor. There are something’s that make logical sense when using a finer grind, i.e.

Small coffee volumes require a finer grind setting for the water and coffee to interact properly. But to say that you should use a fine grind for the AeroPress in all case scenarios is a BIG call.