How I solved my irritating coffee channelling problem
Date Posted:1 February 2016
In this article, we outline some of the steps we took to reduce espresso shot channeling.
No, I'm not about to be the voice of a loved, departed soul, but I will discuss something that is by far the most critically important contributor to improving your consistency in preparing espresso coffee.
For those of you not using a manual espresso machine, you are advised to skip this article completely, e.g. for owners of automatic grind-dose-tamp-espresso machines, stovetop, filters, drip or perc, plunger, pod or capsule machines - this does not really apply to you.
You may have heard me mention channeling before in previous articles. It's a rather dry and technical topic, but I guarantee the benefits dramatically outweigh the effort, so if you truly desire performance improvements to your coffee making skill, then please be patient and persist.
Unfortunately, it's not easy to write about channeling without involving a lot of hi-res images to support in explaining the technical terminology.
Channeling is the result of pressurized water from your espresso shot finding pathways of least resistance to flow through your ground coffee inside the portafilter (group handle) and into your cup.
The result is thin body, lack of flavour, acid and sweetness from a combination of under-extracted and over-extracted coffee.
Basically, less than 100% of the ground coffee was used effectively during the espresso shot. In many cases, depending upon the severity of the channeling, the espresso is less than half of what it should be.
We know the flavour and attributes of espresso coffee are primarily oils and compounds extracted when the variables of particle size (ground coffee), heat, pressure and time are all in the correct proportions.
Any of those variable can be out by a fraction and the result is sub-optimal.
Unfortunately, there are no real tools or methods you can use before you execute the espresso shot that can guarantee this complex set of variables are all completely accurate.
However, you can implement a range of processes that can assist such as analysing the used coffee puck (after extraction), observing espresso shot flow (colour) and time, measuring/weighing input and output of coffee volumes to test total dissolved solids (TDS) brew ratios of espresso with a VST refractometer kit and of course the simplest and best method is the good old reliable "how does it taste".
Another good diagnostic method to identifying channeling is to use a naked portafilter - a group handle that has been machined with no bottom section or spout so you can observe the result of the espresso shot as it exits the filter basket to see visually if the extraction is evenly dispersed.
Below you can see 2 images of a naked portafilter. The first shows the initial stage of the espresso shot and the second shows an almost perfect espresso shot with no obvious signs of channeling. When channeling occurs using a naked portafilter, you will see the flow of coffee will not form evenly in the centre of the filter.
These can be purchased to suit your machine or if you are handy with tools, you can grind off a spare group handle.
Perfecting the espresso extraction should be your #1 goal regardless of whether you drink black or milk-based espresso coffee.
A good espresso extraction will make every beverage you produce taste fantastic without having to hide bad espresso with milk and sugar.
Channelling is perhaps one of the more difficult challenges to overcome with espresso coffee and most surprisingly it tends to afflict both novices and the experienced.
If you think you have mastered the grind and dose it is not unusual to continue experiencing inconsistency as a result of channeling.
Signs of Coffee Channeling
The most obvious signs of channeling are:-
1. Espresso shot starts relatively quickly - sooner than expected, e.g. before complete pressure has built up - it starts with a thin dark watery fluid that blonds soon afterwards and may have alternating stripes of blonde and flecks of darker colours whilst pouring, but predominately early blonding. The espresso shot will lack body viscosity, mouth feel and may taste terrible depending upon the severity of the channeling.
2. A lack of crema, or pale coloured crema (could also be a grind, dose and bean age issue).
3. Weak flavour, one-dimensional, flat, dull, lacking acidity or even bitter taints apparent.
4. Faster espresso shot times on volumetric devices (pre-configured time-based button settings),
5. Larger brewed volume (more fluid/water in the espresso shot) than expected
6. Inspection of the used coffee puck reveals one or many small pin holes.
For the last few months I have been struggling with channelling on one set of my test equipment at the roastery. It's literally some of the best gear available - a new Compak E10 OD Master conical grinder and a La Marzocco GS3 volumetric espresso machine - yet 1 in 4 shots are channelling to varying degrees and the problems have plagued me for too long.
What is frustrating about this channeling is the fact that I know it's channeling (and I've known it since day 1), I also know how to resolve it and I'm annoyed every time I see the small pin hole in the puck when it does occur.
But.......... I'm just like everyone else in the world suffering this same problem - lacking time and more to the point.......patience. I just want my coffee to come out good with the minimal amount of effort, every time I step up to the espresso machine.
My situation in the roastery is a little different to the home user - I have dozens of different coffees to run through and they all require a slightly altered dose and grind setting, so the setup effort is more involved and it's this precise area that I am trying to compensate via less adjustments to grind and dose each time a new coffee is put into the grinder hopper.
What I have been acutely aware of for the last 18 months and failed to act upon is that despite having the best toys at my disposal, my finger has been pointed at those darn VST filter baskets and the ill fitting tamper that are making the channeling problem more frequent than it really should be.
Now, let me clarify why I am accusing the finger at VST filter baskets and a poorly fitted tamper.
VST filter baskets are a revelation in the specialty coffee segment and I have been a fierce supporter of these baskets since the month they were released on the market. They have been around for many years now and grown in acceptance as the pinnacle de-facto standard in espresso coffee excellence. The laser etched holes are remarkably consistent and when everything is working well, you will never make a better coffee. Without the doubt, the VST's help you conquer that last 5 - 10% improvement in espresso coffee extraction when you hit all the right variables.
With such performance opportunities available there has to be a gotcha - it comes with some conditions or let's say considerations. The holes in VST filter baskets whilst more consistent in shape are actually a fair bit larger in diameter than standard espresso filter baskets and this means you need to grind finer and/or dose higher.
The holes in VST filter baskets are also manufactured right up to the edge walls of the basket to create a larger surface area and enable full extraction of the ground coffee.
Whenever you grind finer, there are a few things that will happen - the ground coffee may clump and compact in certain areas and your dose levels need to be more precise. The compaction of the ground coffee is perhaps more difficult to manage as you need to distribute the coffee within the portafilter carefully before tamping.
Distribution is key to avoiding channeling and various techniques can be used such as tapping your tamper on the side of the portafilter to "settle and break up" the grounds, allowing the ground coffee to pack consistently before tamping. Another method to distribute is to allow your portafilter to be tapped on a surface although that does not work so well if you have a single spout fitted. Other methods involve using various dosing tool like a piece of plastic to level off the grounds. Some people also use a light pre-tamp with a twisting or nutating action to gently spread the grounds. There are new products on the market these days that focus just on ground coffee distribution but they are primarily targeted at the specialty cafe baristas and home entusiasts.
The finer you grind, the more critical is becomes to ensure distribution of the ground coffee within the portafilter before you tamp as the risk of compaction and channeling increases. Finer grinding also means you need to be careful with tamp pressure and ensuring the tamp is very level. Tamping hard with a fine grind will increase the risk of channeling or choking the espresso machine. An uneven tamp will promote channeling as pressure will pass through the lower side.
Most espresso machines use 58mm filter baskets. The design of many VST filter baskets can be slightly larger than 58mm, e.g. mine are actually 58.5mm which means that most off-the-shelf 58mm tampers are a fraction small for my VST filter baskets.
People who are serious about their coffee performance are more inclined to purchase a custom made tamper - where the tamper is machined to fit precisely with the filter baskets.
Whilst it is hard to imagine without actually experiencing the problem is that 0.5mm does in fact make a difference. I had been using a stock 58mm tamper for 15 years and they don't work with my VST filter baskets and my La Marzocco machine.
Whenever I have a channeling problem, I immediately inspect the used puck and 100% of the time I have found that the pin hole (or holes) are along one edge (wall) of the puck. Because I know this is likely to happen, I try to prevent channeling by tamping with the nutating technique of running the tamper lightly around the edges of the portafilter in a circular motion, twisting and polishing to ensure an even distribution of the ground coffee before applying my final tamp. I call is shaping.
Despite all the careful distribution of the ground coffee and compensation for a slightly under-sized tamper, it's still not working to the level of consistency I desire and of course this 25% channel rate is extremely annoying.
To resolve the problem of a slightly undersize tamper, I am now using the new 2nd generation The Great Leveller tamper, which has been revised with an increased size of 58.5mm to specifically suit VST filter baskets - saves having to get a custom tamper made up and solves the uneven tamp risk at the same time.
Roughly speaking, the reduction in channeling has been around 65% which was both pleasing and worthwhile.
So like a dog with a bone, I was not going to let this remaining 35% go unresolved..........so to finish off the story about how I reduced channeling in my setup, I eventually caved into my frustration levels and swapped out the VST filter baskets that I had been passionately loyal for so long to the now use Espresso Parts (EP) Precision baskets.
The picture below shows the VST filter basket
Below is the EP Precision basket I am using now
As I had known for so long now that the channeling was occurring along the edge walls, the holes in the EP baskets stop some distance out from the edge and this has basically solved that edge wall channel so apparent in my own setup.
All images courtesy of Google Search.
DISCLAIMER - In relation to my comments on VST filter baskets - we have not and don't currently sell filter baskets - so I have no commercial bias whatsoever towards VST or EP. I find no fault in the design or manufacturing of VST filter baskets and still believe under the correct conditions they are unmatched in performance, it's just the tolerances were not compatible with my time and patience levels having to prepare coffees from multiple samples at short notice.