Are you a “knocker”?

Here is an edit of a thread I first started on my Barista UK Facebook group a year or two ago and thought I would share it here;

A few years ago I read an article about tamping on (in between my party-hard active life obviously!… ahem…) At the time it totally changed the way I though about espresso and the processes we go through.

The article was talking about tamping techniques. In short La Marzocco were developing an auotomatic doser/tamper that dosed into the porta filter as it tamped. It was set to 30lb’s right away and the espresso wouldn’t extract at all! I think in the end they had it down to about 8lbs of pressure to get extraction. They looked into it and found out that the auto tamper was adding progressive pressure throughout the dose in complete contrast to a normal tamp which transfers energy from the top of the cake. Anyway, after some research it was found out that under normal tamping the compression energy is lost and only actually compresses a couple of mm at the top of the cake. The rest of the coffee underneith remains loose!

This then brought about the thinking of the normal “tamp, knock, polish” thing that a lot of us do. The suggestion was that knocking the portafilter (now we do it for an important reason – and it’s still obviously a good thing) was loosening the cake even more and detremental to the extraction.

The guy writing the article did loads of research and found that using a convex tamper 2 mm smaller that the diameter of the basket gave the best results. Instead of knocking the side of the portafilter he worked out a technique to rotate the tamper on it’s convex all 360 degrees. This meant that the knocking wasn’t needed and the cake wasn’t disturbed.

This really intreuged me…….Basically at was a big eye opener to…er….keeping your eyes/mind open to new things and not get stuck in the “my was is the right way” thing…..

I would love to hear any theorys that you guys have and the tampers you prefer.


The original coffee Geek article;

ADDITION: Since posting the above I have played around with the different techniques and found that tamping and then polishing without the knock produced the most consistant extractions with more soloubles. Maybe because of the reduced risk of channeling?


~ by Lee Wardle on February 8, 2010.

2 Responses to “Are you a “knocker”?”

  1. Nice to be on a fresh new coffee blog…
    Looking forward to seeing what cool posts/discussion come up!

    Let me start this new post by saying the following:

    “My name is Billy, and I am a knocker!’ – There, I said it…

    I know that there can be a little displacement when you tap the side of the basket, but to be honest, to try and stop this, would be like trying learning to write with my other hand… I’ve been ‘knocking’ for so long now, it would feel super weird not to do it.

    I have tried dipping the handle part of my tamper in a rubber goo stuff, that has basically taken the harsh crack back a notch or two… It still loosen the grinds from the side, but doesn’t seem to crack the cake…

    Did that make any sense at all?

    My wife keeps telling me I write way too long sentences! Sorry…

  2. Ha ha cheers Billy! Yeah, wierd trying to program your brain to change after soooooooo long! They say that any process takes 19 concious go’s before it becomes a habit? (so Many jokes so little space) so 19 “no knock” Tamps and you’ll be cured!

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