Hello,

I have spent the whole day watching the WBC semi-finalists, live on the WBC website. Having read several times Scott Rao's great handbook, one thing stroke me: almost all participants are doing the second group's mandatory flush while the first group is brewing...

This is completely wrong according to Scott Rao, page 32 at the end:

While a shot is being pulled, several events can temporarily decrease pressure. (These concerns do not apply to lever machines)
1. Purging or flushing another group
...
Such variations in pressure can promote chanelling in the original shot and should be avoided whenever possible, ...

We all know that levers are better since they cannot be disturbed this way, but I really wonder if La Marzocco machines have special technical wizardry to maintain brew pressure when one flushes another group.
If not, then I don't understand why WBC participants are not sanctioned...

why WBC participants are not sanctioned...

Sanctioned? Images of grim-faced men in suits with large hand guns...

Matthias,
Maybe this coffee making business is not that certain. If its a competition and they are making bad coffee then they get penalised. No need to legislate how to use the machinery; we just aren't that sure how this stuff works.

Greg

matthyx wrote:This is completely wrong according to Scott Rao, page 32 at the end...

Hmm-m. Has someone taken measurements demonstrating this pressure drop, and if so, how much is it? I haven't, but I wouldn't expect a measurable drop because espresso flow rates are a tiny fraction of a rotary pump's capacity. Next time I'm at Counter Culture's espresso lab, I'll try to remember to measure their three group La Marzocco.

There are a few different answers to the question.

*The political answer: The rules have to be acceptable to many different countries, so changing the rules to include this as a requirement would take quite a lot of effort.

*The timing answer: You cite Scott's book, but omit reference to the footnote, which acknowledges that this may be impractical. If you watch all of the competitors' routines, you will see that if they wait to do that three times, many of them will go over time.

*The measurement answer: Does someone want to go and actually measure this? From memory, I think that the pressure drop from flushing isn't that much ... maybe a bar or two, but, to tell you the truth, I can't remember if that was with or without the accumulator tank. Then there's the gicleur to slow the ramp-up.

*The bottom-line answer: Scott says that you shouldn't do this because it might make your shots channel. If that happens, you can bet that the judges will penalise the barista on sensory. If it doesn't ... then what's all of the fuss about? Remember that all of the WBC competitors have won a national competition to get there ...

For me, your question highlights what is a big problem not only with Scott's book, but with most books: they're great at setting out the steps, and Scott's book does a particularly good job of summarising current theory, but they're all pretty terrible at setting out the relative importance of each of the factors and the magnitude of the impact that they have on the resultant cup. This is, I feel, a particular problem with Scott's book because he does such a great job of setting out so much theory. Whilst I have no doubt that everything that Scott talks about makes a difference, I think that there's a risk that people will obsess too much about the minutii at the expense of focusing on the cup and on the factors most likely to make a difference to it. To give you an example; yeah, grinders that really heat up might suck unbelievably, but if you're only making two shots a day, it's difficult to see that that's going to be an issue ... but the reader has no way of knowing that if they take page 8 at face value.

Cheers,

Luca

coffeefrog wrote:Sanctioned? Images of grim-faced men in suits with large hand guns...

Ok, maybe the word is too strong, I should have written penalised, another problem of not being a native English speaker

HB wrote:Hmm-m. Has someone taken measurements demonstrating this pressure drop, and if so, how much is it? I haven't, but I wouldn't expect a measurable drop because espresso flow rates are a tiny fraction of a rotary pump's capacity. Next time I'm at Counter Culture's espresso lab, I'll try to remember to measure their three group La Marzocco.

Thank you Dan, I expect a pressure drop because while one group is brewing at espresso rate, the other is flushing so the rate is x-times higher.

I think this may be why some participants prep both portafilters and start brewing at the same time: the brewing flow rates do not draw the rotary pump capacity and espresso quality does not suffer.

Luca, thank you for your very detailed and precise answer. If the pressure drop is only one or two bars, then it might not impair the shot quality.

I fully agree agree with you on the judges and shot taste, but I think there are also different judges that focuse on technique and for example watch if competitors remove loose grinds from the portafilter before inserting it in the grouphead... but again I am very new to the WBC world.

The definite solution would be to get CMA or another commercial lever manufacturer to provide lever machines for the WBC and that could be the next level for our LMWDP project

matthyx wrote:If the pressure drop is only one or two bars, then it might not impair the shot quality.

Of course, the pressure drop over the course of the stroke with a coil spring lever might be about two (a drop of maybe 25% for a lever), but I'd be unsurprised if it were more...

irrelevant aside: I sometimes wonder how different a profile the original Gaggia lever group has with its torsion spring as compared with the profile of a conventional coil spring lever.

luca wrote:grinders that really heat up might suck unbelievably, but if you're only making two shots a day, it's difficult to see that that's going to be an issue ... but the reader has no way of knowing that if they take page 8 at face value.

They might get a clue by noting that the book is called, "The Professional Barista's Handbook."

Any professional barista that makes two shots a day is going to become an amateur barista in short order.

Not if it's 5 grand a shot