My name is Mike Mac Donald. I am a Coffee Roaster.

The purpose of these blogs will be to instill a sense of ‘coffee-logic’ within each and every one of you. I will be sharing what I have learnt along the path and push forward ideas of anything that might seem relevant for the betterment of the coffee industry and for the curious of the craft.

Today I will talk about the Aeropress….and why people love it.

A few years ago I decided that I needed to know more about the complexities in coffee that modulate flavour, dependant on grind size and water temperature.

One aspect of a coffees cup profile that is certainly maleable in this way are the Acids.

To understand how to tweak flavour in the Aeropress in this regard, we first need to understand what acidity is.

The perceived acidity of coffee results from the proton donation* of acids to receptors on the human tongue.

*Acids are substances that can donate H+ ions to bases. Since a hydrogen atom is a proton and one electron, technically an H+ ion is just a proton. So an acid is a “proton donor”, and a base is a “proton acceptor”. The reaction between an acid and base is essentially a proton transfer. the term “hydrogen ion” or “hydron” is generally synonymous with the term “proton” (the atom has lost its one electron, and thus one proton is all that remains). Source- Wikipedia.

In this way, think of it more as a sensation than a taste. Acidity is a highly valued aspect in a coffees profile, especially from high quality varietals out of Central America and East Africa. As just one example: the ‘Juicy’ sensation one would experience from biting into an Orange is possible to replicate in a cup of coffee. However, one has to remember that it’s a cup of coffee you’re drinking and not an Orange that you’re eating. There’s a great deal of other stuff going on.

The acids make up about 31% of your brew and add some serious dimension to the overall flavour. Favourable acids make the cup more complex. Washed coffees have a prominent, clear acidity potential compared to Natural or Pulped Natural coffees.[A separate blog on processing will be posted in the near future.]

Ok…..got that? Let’s move on.

The extraction of acids in your brew is highly affected by water temperature, grind size and lastly extraction time. However, the latter is something we will not consider as we will almost always, by default work within desired extraction times( for various reasons of course).

One of my favourites that I am constantly chasing and trying to understand is Phosphoric acid, which is said to bring out a berry-like flavour in the cup (More correctly, modulates the cup towards a perception of Berry) .

Especially found in the great SL28 varietal developed in Kenya by Scott Laboratories, this bourbon strain has an ability to uptake more phosphorous from the soil which converts to phosphoric acid in the cup. Phosphoric acid creates a tangy ‘snap’ and/or slight sourness to your brew. Unfortunately not enough solid research has been done to clearly identify differences in acid levels amongst varietals. That being said- Phosphoric acid exists in all varietals, but there is no reference guide to this information……..at the moment.

THE GRIND SIZE.

A finer grind will yield a much higher amount of phosphoric acid.

A friend of mine, and fellow coffee fanatic- Dave Coleman, enjoys his Aeropress brewed with a much coarser grind( closer to that used for a Plunger).

That’s great too. In fact, he’s technique extracts lower amounts of that nasty stuff, Chlorogenic acid( this adds to the total perceived bitterness of your cup).

This is one reason why the Aeropress is so awesome, it’s incredibly versatile.

Kudos to you Coleman, for keeping it real and portraying Aeropress brews that are clarified and sweetly elegant.

For those of you who wish to potentiate your brew and add a little more phosphoric to the cup- work with a grind between espresso and filter.

THE WATER TEMPERATURE.

So how low should you go with water temperature to extract enough phosphoric acid without negatively affecting the rest of the brew?

Starting temperatures of 85-90° C( 185-194°F) work really well.

I personally prefer 88°C( 190.4°F).

What’s that I hear you say? You don’t have a temperature probe?!

Get with the program!! What are you? Second Wave?

Finer grinds and lower temperatures will yield higher levels of Phosphoric acid than courser grinds and higher temperatures. For more information, check out- http://www.coffeeresearch.org/science/sourmain.htm.