Prufrocker: The Blog

Primitive Scales and Advanced Grooming

A new work flow developed to balance precision with sustainability.

by  |   |  Coffee Science

18g on the primitive scales.

On Prufrock’s bar are two Slow Speed Barista Mythos grinders, development versions of what lovely Mr Harmon has blogged about recently.

“There was a time when it wasn’t uncommon to see people finger-swiping the excess coffee out of the portafilter and into a bin (A BIN!!)”

Well I’ll be honest, the time he refers to was about two weeks ago at Leather Lane.

For about 18 months we have had access to these marvelously low retention grinders (4g retention max, so there’s no need for the 40-60g uber purge). We weigh every dose down to 0.2g, so we are accurate to +- about 1% (about the weight of a single bean). This accuracy is what permits a barista to remain on the optimum shot time within a very small margin of error. Accuracy of dose and effective regular micro-adjustments of the grind have long been the hallmarks of a great baristas. All the WBC technical scoring for ‘consistent dosing and tamping’ is structured around the traditional expected skill set which has flagged up a few issues.

After dialling in, adjustments in grind are really re-calibrations of the grinder to compensate for changes in the aperture between the blades caused by heat. Grind changes are also necessary because of changes in grind morphology cause by hot blades on hot beans. We look to the Clima Pro to dispense with this need. A grinder audacious enough to displace (or rather move one step to the left) coffee’s latest it girl. Portion control with the EK is precise but labour intensive. What still isn’t perfected in our experience of grinders with a hopper system is precise automatic dosing. Baratza have come close with their admirable built in scale (+-0.2g with the odd outlier) and 54mm burrs.

Sometimes 6.85 seconds of grinding gives you 18.0g and sometimes it gives you 19.4 or 17.7 in all grind on demand grinders we’ve used. You might need to top up. And sometimes you top up a touch too much and you need to trim half a gram or so and the question a costs-focused barista wants to know is: where do you put it? You used to have an opened top manual dosing chamber to trim into. You could sell it to students? Or use it to make Crazy Eyes Pete (the lead singer of Lungo) a coffee? Or maybe you pop it in the knock box, “A BIN!!)”. It’s only about two coffee beans per shot. This is a good deal less than we used to discard.

In my early coffee lessons a very high mound of coffee grinds in the basket was the done thing as it would mean after a finger strike the coffee would be distributed evenly. I’d say this worked quite well. Grooming will only affect the top millimetre or two of the coffee cake. It’s more important to dose symmetrically than to groom the top section neatly. At the London Barista Resource with VST baskets we encourage you to do both perfectly. The real trouble with the old method was that if you plonked 25g into the basket then finger swiped level to the top of an 18g basket, it might give you 21g and if you dosed 20g then finger swiped you might get 19g and only an optimum 18g estimated dose would actually fill the basket. Coffee is highly susceptible to being compressed under its own weight. Many top baristas, including the Coffee Maniacs of Moscow with plenty of technology ast their disposal just estimate the initial doses by eye and have found themselves to be more accurate than trusting a timed dose. They can then verify the weight on a scale. The key is to not over estimate.

Five years ago quality baristas had mastered the art of estimated dosing with precise NSEW or Stockfleths moves but the squarer shaped VST precision baskets which we adopted were a bit more difficult to estimate doses into. I just initiated an impromptu in house barista blow-down with four of our senior baristas for estimated dosing with a target of 18.0g. The results were Barista 1: 16.1g, barista 2: 17.1g, Gazza 18.0g, Director of training 18.0g. The 16.1 and the 17.1g come from the scales generation. Interestingly no one overestimated but it can be the topping up that bumps you over the target dose. It is also considered better to not go off and on the power button as your grinder will be operating at slightly different RPM as it stops and starts so you may end up with very inconsistent grind morphology. Received wisdom says it’s best to get a hole-in-one.

Anfim manual dosing chambers are famed for clump breaking and good sifting (aerating) of grinds. Assuming you dose and grind simultaneously. The grinds are also dropped quite vertically into the basket rather than being flung off to the left. Gwilym and Morrisey took this system to the WBC but I have heard Gwilym say, “I’m too old for manual dosing”. So am I. Hard not particularly diverting work and loud. To get a sense of how ear piercing this archaic method of dosing is, picture yourself in a cafe in a lumber yard sitting next to a woodpecker. Further more, all that clicking it is very hard physical work for baristas in high volume cafe models. If you’re on 500 coffees a day, that’s a good 5000 clicks.

In order to find a solution to this we have opened a leaf of the Simonelli grinder back catalogue and have installed a manual dosing MCF grinder in between group 1 and the Mythos grinder, not for its grinding abilities but to make use of its low resistance, fairly quiet manual dosing chamber. Estimate the dose on the Grind on demand and trim any excess into the right side of the manual dosing chamber. Now we are no longer throwing away any un-extracted grinds and it’s projected to save us £1368.75 this year based on the Red Brick wholesale price and 0.5g wastage per dose at 500 coffees per day. With Prufrock’s accounting factored in we have been needing to make an additional £13k per annum to break even on this level of wastage.

This is the new work flow:

Customer #1.

Make a coffee. (18g delivered accurately) Smile at the customer. Share coffee knowledge if solicited.


Customer #1. Making the coffee, weighing the coffee.


Customer #2. Finger strike!

Customer #2.

Tare, dose, groom, weigh, 18.4g delivered, finger strike into the MCF open topped manual dosing chamber.


#Customer 3

Customer #3.

A couple of clicks from the manual dosing chamber of the MCF for the 0.4g excess from customer #2


#Customer 3. The Mythos.

Then over to the Mythos for the remaining 17.6g.

So is there a loss of aroma from the 0.4g we salvaged? Well consider it was ground at the same time as the 4g that is retained each coffee you make. So this issue is ten times worse in a 40g retention 50s style grinder.


The low retention grinder.

The grinder is very low retention because much like the Bunn G2 and the EK43, it has it’s burrs angled towards vertical (though not totally vertical like those two) so the long throat between the burrs and the portafilter has been done away with. Also the width between the burrs and the edge of the barrel is only around 3-4mm so there is much less area for grinds to accumulate before they squeeze their way out. We are moving away from high retention grinders. This is especially critical for guest coffees for reasons of freshness. Coffee wastage is as much an issue of respect for farming practices as it is about drinks quality. This new work flow has been developed to balance precision with sustainability.

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