Puck preparation

On the Londinium support forum, Matt asked

I've been experimenting with different patterns of moving the grinds with the distribution tool, but I've yet to settle on one. If I swirl it about the edges, I end up with a hole in the centre; but if I swirl closer to the centre, I end up with walls of coffee rising over the edges of the basket on one side or another. On the other hand, if I just trace out random patterns, I get random results. What do others do?

The routine that works best in my view is simple. I do a random stir, a brief shake, a tap, mild press with the flat tamper, lock in and go.

Still there is more to say about the details.

Fluffy
In my experience, most grinders produce a mixture of loose grinds and 'boulders', fluffy 'snowballs' of grinds that have locked arms and came tumbling down the chute together. The 'boulders' start to appear when the grind is exactly fine enough for espresso and this can be a point of reference when dialling in the grinder for a new pack of roasted beans.

Life span of beans
Freshly roasted preferably, assuming the beans have had a few days time to rest right after roasting.

During the weeks post-roast, well roasted beans often go through stages of resting and ageing which can all produce excellent and interesting espresso. The first days, a bean that hasn't had enough time to rest may be capricious to extract, with a haphazard flow and some worrisome sharp taste weaving through the otherwise very promising flavours and aromas. I think of it as the 'puberty' of the bean.

Then, for about a week or so, the taste gets better and better and any worries that one has got a bad roast are quickly forgotten. Everyone would like those beautiful shots of the fully matured and creamy espresso.

It's wise to buy more than 250g of a roast because the you get the chance to explore and enjoy the rich and mild taste of the week or two after these first 3-10 days. Any sharp edges have vanished completely and it seems only the best qualities gently flow into your cup. The beans will not get old for a while but they have aged beautifully, kept away from direct sunlight and the espresso is as much a mild wake-up treat in the early morning as it can be a sweet and energising last cup in the late afternoon.

Some beans can be very surprising as they stretch their life well into the 4th week but eventually the mildness becomes bland, the flow gets too fast and if one tries to push the elderly beans to the limit, tightening the burrs, the beans can again begin to yield some unpleasantness, a woody taste, a sign that it's time let go and move on to the next exciting roast.

Particles
Coffee grinds are often, in theory, compared to a mix of particles like ping pong balls, of different sizes. One can use sets of different sieves to try to separate these different sized particles but when you look at coffee grinds through a magnifying glass or a microscope you can observe that the grinds are more like shredded particles which tend to clog together. Of course one could shake and rub these fluffy grinds over holes of different sizes and then a lot of them will get stuck in holes, let go of their company particles and fall through but what one is then 'measuring' is maybe as much the result of shaking the bulk of grinds as it is the result of the grinding.

Distribution
It certainly does help to distribute the grinds quick and thoroughly, since most grinders produce grinds that come swirling out of the chute, landing in the middle, building a cone in the filter basket.

One needs a distribution tool that doesn't just move heaps of grinds like a tiny spoon would and also not a single wire or tip like a syringe which would merely break the little boulders. There are also devices like a tamper with bumps on the bottom that are twirled on top of the grinds but these merely compress the cone in the center and flatten the top of the grinds without distributing the full depth of the grinds. Some baristas wipe the top of the grinds with their fingers or other tools in gestures that sometimes have even been given names but in my view superficial swipes are not very effective. These rituals serve to enhance the magic of the barista more than they improve the espresso ;-). In nimble hands a mini whisk can be useful if one makes sure to reach the deep corners of the basket.

The antennae of a tool like the Londinium Distribution tool are small enough to easily reach into the deep edges of the basket and big enough to move grinds around and at the same time it makes it easy to create a fairly even fluffy load of grinds to be mildly compressed using a flat tamper.

Shake and tamp
I made it a habit to give the portafilter a little shake before I lift the distribution ring, followed by a brief tap (or two) so I can see that the grinds have indeed been evenly spread out.

The flat tamper needs only a mild pressure, provided that the beans are fresh. A machine with low pressure pre-infusion like the first generation Londinium, or current boiler pressure pre-infusion machines like the QM Achille would still need a very light tamp so the low pressure is still enough to infuse all of the puck in a fe seconds.

Permeate
One needs the puck to be tightly packed just enough to remain intact as water hits it in the brew group but not packed so tight that the puck actually resists being permeated by water. If the puck is packed too loosely, the water raining down on it may disturb the grinds, creating holes and crevices allowing a fast and chaotic flow, resulting in unpleasant coffee. The same would happen when the beans are getting old and if so, pressing harder with the tamper may improve the flow but won't save the coffee shot.

Transformation & flow
As the grinds get thoroughly wet, the puck which was merely a weight of loose grinds packed together, transforms into a different and very interesting body. It's become something in between a gel and a puck, a juicy elastic body which responds to the hot water applied at pressure on top of it by allowing an outflow of the best it incorporates.
After initiating the pre-infusion by pulling the lever of the espresso machine, I mostly wait about 5 seconds before releasing the lever. Then, the pre-infusion pressure of 2-3 bar is replaced by the spring pressure that starts at 8-9 bar and gradually declines to around 3 bar before one pulls away the cup, disregarding the remainder of the extraction.
The first droplets may appear at the perimeter of the bottom of the basket but a moment later all basket holes are filled with the first dark and oily extraction and in one smooth flow the volume of the stream increases, from a few voluptuous droplets splashing into the bottom of the cup to a widening tail of espresso showing off different hues of golden brown.

Brew ratio
Mostly, when I take a dose of 18g in the 18g basket, I aim for a flow of about 30g of espresso in around 30 seconds. For lighter roasts, I dose a little more, grind a little finer, I raise the pre-infusion pressure, allow pre-infusion to last a few seconds longer and I aim for about 25g in 25-30 seconds. For darker roasts, I may dose less, grind coarser, use a lower pre-infusion pressure, release the lever as soon as the pump stopped working at pre-infusion and aim for a flow yielding up to 36g in 30s.

Scales
A scale like the Acaia can be essential or at least very helpful while dialling in the grinder and monitoring the flow.
Once this has been done however, you can relax and merely enjoy the results.
If the grinder produces 0.4g more grinds than expected, you'll still be fine and the resulting taste may be a little more intense while not introducing unpleasant bitterness.
If the grinder produces 0.4g less grinds, the flow may be a little faster and the taste may be somewhat more expressive, like a fan opening up to display more of its printed pattern yet not introducing unwanted acidity or the watery taste of vendor machine coffee.

Grind by weight?
These days, the newest and hippest grinders offer a "Grind by Weight" option. At first sight that would seem a great idea. These grinders incorporate a highly sensitive scale weighing the portafilter and some slow down their grind speed to make sure that the grinder transports the exact same weight of grinds every time.
Many baristas assume that grind speed affects grind quality and while not everyone agrees about the best RPM speed for burrs, changing the production speed to finish at the precise weight may be introducing one compromise to trade for another.

Timer control compensation
What I like very much about the common timer-controlled grinders is that they automatically compensate for any small change in burr setting which may be caused by small variations like a temperature difference. For instance, a grinder dialled in at a cool early morning hour may later in the day be surrounded by customers and the cafe may be ten or more degrees warmer. As a result, the teeth of the burrs may be pushed a tiny bit closer together or a little wider apart.
If the burrs are closer together, the timer setting causes the grinder to grind a little less in the same time and the other way around, on the same time span the grinder will grind a little more when the setting got coarser.
In consequence, the slightly larger dose of coarser grinds will mostly work just as well as the original setting did and the finder grinds in a smaller dose will also set you up for an excellent shot.
Sure, the shots will not be exactly identical but they will be just as excellent each in their own way.
A "Grind by Weight" grinder will, when the burrs settle little differently on a warmed up or cooled down day, not be able to compensate and the barista will actually be required to adjust more often, which was not the idea behind the new optional extra.

Keep shower screen clean
If you treat the beans and the grinds right, it may happen that the extraction looks sloppy, as if the puck is broken and pale coffee water is gushing out of the portafilter instead of a beautiful steady flow of espresso.
In that case, check the shower screen and if you haven't just done it, give it a thorough clean in a soapy detergent specially sold to clean shower screens and portafilter baskets.
Sometimes, excess grease from a brand new group can slowly drip onto the shower screen and since it's transparent grease, you can't easily spot it but it's keeping many holes clogged up so the water that is supposed to rain evenly dispersed onto the puck is pressed through the remaining holes at great speed and force, like when you squeeze the end of a garden hose. This rips up the puck before it can get all wet, so it is not allowed to transform into a firm and flexible gel producing delicious espresso.

Above the screen, most machines have mechanical designs to ensure that the brew water lands as gently as possible onto the shower screen. In a Londinium brew group, four jets of water enter the chamber above the shower screen and they meet in the center, splashing into another and from there raining down on the shower screen (which I took off for these pictures, made by me in 2013) to allow a better view of the water: