A number of people have been seeking advice on ICM lately, so I thought it could be worthwhile posting some videos. INSTRUCTIONS:
Important points to consider:
ICM does not replace WDT - WDT is critical in my opinion, so ensure you have invested time into mastering this technique. Everyone has different approaches to WDT, mine is as follows:
Chop down mound before starting.
In a non-stop motion, start with tines scraping the bottom of the basket (i.e. full depth), performing smaller swirls around perimeter of basket ensuring corners of basket are targeted.
Then, without stopping, move to full-width central circles and gradually rise upwards while continuing to circle.
Finish by levelling top of the bed.
The first aim of ICM is to decrease mass at the perimeter. No matter what the dose, basket, grinder, coffee, profile, etc., all require the mass of coffee around the perimeter to be reduced for ICM to have the desired effect. This is done by shifting it inwards.
It's important to make sure the tines of the ICM tool reach into the bottom corners of the basket.
The combing action should start from the bottom corners and move diagonally upwards and inwards in one motion.
The second aim of ICM is to seek balance in extraction efficiency between the perimeter and the centre. This is a variable that is affected by a number of things and needs to be observed and tweaked. Ways to observe include:
watching the base of the naked portafilter: You should see coffee emerge from the perimeter first, before moving to the centre in an even fashion. The speed and manner in which it moves into the centre will suggest how the applied ICM is balancing the rate of extraction from the 2 areas.
observe the base of the spent pucks: dark patches imply lower extraction, lighter patches imply higher extraction. Ideally, the colour from perimeter through centre is uniformly light.
Dark patches in the centre imply too much mass in the centre.
Dark patches at the perimeter imply more needs to be shifted from that area.
Light patches in the centre imply not enough mass in the centre.
Some general guidelines regarding doses and baskets.
15g doses are shallow, and therefore need more mass to be built in the centre. When trying to increase central mass more, I imagine folding the coffee 'up and over'.
22g doses are deep, and therefore do not need much additional mass built in the centre. They do however benefit from more coffee shifted away from the perimeter. In this case instead of moving 'up and over', I simply comb inwards and upwards to push the edge inwards.
18g doses are somewhere in between.
The Tools! I think a straight row of 0.4mm needles is best. I use a standard B-string for an acoustic/electric guitar and cut it into 10cm lengths. I also fan it slightly.
Below are 2 video examples of my WDT and ICM routine: one shot from a front view, the other from an overhead view. I hope these provide enough visual example to be of assistance.
Next to each is a video of the associated pour to demonstrate the resulting extraction behaviour.
EXAMPLE 1 - Front View: 15g dose - building a larger central mass
