The importance of being wrong

I feel it is about time I broached this subject.  With an eye to the last posts, as well as to the response to my Chemex videocast, I feel the need to make something very clear.

The internet is full of information, though it is also full of keyboard heroes, and has something of an issue with its signal to noise ratio.  Identifying who is a useful purveyor of information is tricky and, while there is growing use of indicators in forums, often it is he who shouts loudest that wins.

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More on the French Press Technique

After the last post there was a bit of discussion about this method.

One big question was:  “Why break and then skim?  Why not just skim?”

This seemed like a pretty good question to me, so today I decided to do a few quick tests.

I took two identical presses, the same dose of coffee, the same brew water, temp and time and then after 4 minutes broke and cleaned one, and just cleaned the other.  I then tested out the TDS in each cup of coffee.

A TDS meter is useful, but limited.  It will tell you how much is dissolved in the water and nothing more.  Here I wanted to see if one cup was stronger than the other.  It turns out one was – and by quite a significant percentage. 1

The broken and stirred cup was stronger, usually by around 0.2%.  This doesn’t sound like much but when you do the maths backwards you find that it is a swing of about 3% of the ground coffee solubles extracted into the cup.

I want to do some more tests on this, and I want to do some blind cupping of it as well.  However it would seem that if your grinder produces a lot of fines, and when making press coffee it seems to easily overextract then I would just skim, opposed to breaking and skimming.  It could be that a different dose and steep time could yield better results.  I am waiting for Mark Prince’s article on his press technique because I know that while he skims but doesn’t break he does use different parameters.  It may be that one style might highlight a certain coffee better than another, who knows – I am just interesting in learning more about all this.

  1. It should be noted that I haven’t done this experiment enough times for it to be seriously useful – if anyone out there with a TDS meter wants to contribute then please do!  ↩︎