A grand unified theory of espresso

May 7th, 2009

Not too long ago I posted on Home Barista about trying to find a good way to measure the density of coffee beans.  1

As always the paricipants there were way smarter than me and offered several interesting options. I dropped into the thread that this was part of my idea of a grand unified theory of espresso, and subsequently a few people mailed and pm’d me asking what on earth I was talking about and what density had to do with it.

Well, I should probably explain what I have been thinking.  2

When approaching a coffee and brewing it using an espresso machine you are often searching for an ‘ideal’ recipe for that coffee.  For many of us knowing as much about that coffee as possible often helps make intuitive judgements about things like dose and brew temp.  If I get my science wrong then please, please shoot me down.  3

One of the things that broke my head about roasting early on was the discovery that the longer/darker you roast the less potential solubles you have.  This may seem obvious to some but it always felt like the roasting process created many new flavours but one must distinguish between flavours and solubles.  This explains why instant coffee is roasting very fast and relatively light – they are interested in a percentage yield so the more solubles the better, regardless of taste.

Knowing this then made something I had experienced make apparent sense – darker roasts generally prefer higher doses, because you need more coffee to get more solubles to get a nice, thick and pleasant espresso.  But after a moments thought it didn’t make sense.  This would mean that you would get a thicker, heavier cup with a higher TDS measurement from lighter roasts but lighter roasts generally produced delicious but lighter bodied cups.  What nudged me towards density was how we approach very high grown coffees versus lower grown coffees.

Higher grown coffees (and let me make a broad sweeping generalisation here) have a much higher acidity than their lower grown brethren.  When brewed as espresso they can easily yield extremely acidic and unbalanced cups and, taking unbalanced and pronounced acidity as a sign of underextraction, I found that higher brewing temperatures helped to produce a more balanced cup.

What do lighter roasts and high grown coffees have in common:  higher densities.  Though there was more to extract (in theory) you had to work a lot harder to do it.  Therefore reducing the dose of a lighter roast/higher grown coffee gave you a higher ratio of water/energy to coffee to help extract a tasty cup.  (I often think of heat energy as some sort of currency, with which you can buy solubles.  The more heat, the more you extract/purchase.)

This is all well and good for convenient examples – high grown, light roasts versus low grown darker roasts.  Give me a clean prepped coffee from relatively low altitudes in Brasil, roast it into 2nd and I will likely be dosing quite high and not brewing too hot.  I’ll certainly be dosing it very different from how I might brew a lot of Aricha as a straight shot.

But what about a light roast of a low grown coffee, or a dark roast of something grown super high up?  This is what lead me to wanting to find a way to measure and compare the densities of coffee beans to see if there was correlation between the density of the end product and an ideal brew temperture of particularly effective dose.

So – if I have had such a good idea why don’t I do all the research and then publish it all at the end of it and try and stamp it “Hoffmann’s theory” or something equally absurd? (Apart from the fact that it is absurd).  Because I want to generate a little discussion about this.  I want people to weigh in and tell me I am being stupid/simplistic and to suggest better ways to test these ideas.  I want to understand espresso better so I can make better tasting drinks and translate coffee’s journey more transparently in the cup.  4

I really hope people will offer their opinions on this idea, shoot it down or take it and run with it.  I am going to start doing some basic testing and see what happens.  Lots of little experiments appeal.  5

  1. There really is no better place on the web for these kinds of questions!  ↩︎
  2. Some of this is based on personal preference, some on what seems to be fairly well agreed upon within the community of people who worry a lot about their espresso.  ↩︎
  3. There is another post in the works about the value of being wrong and discussing it afterwards – yes, I have a big wrongness to confess to…..  ↩︎
  4. I know this is a wordy post and all, and I would have put some nice photos in but my camera is dead  ↩︎
  5. For example – if I roast two coffees til their densities match – will they grind the same, and at the same dose will they extract the same?  Would they be ideal, therefore, to blend together to get the most out of each of them.  This probably shouldn’t be a footnote, but it is.  So there.  ↩︎

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