What is channelling?
Channelling in the coffee world, whether it be for espresso coffee or filter coffee is basically an unevenly extracted coffee: to the extreme.
This is bad.
I’ll talk more about extraction soon, but basically you want a certain level of coffee solids being absorbed by the water you’re using for your brew. We call this an ‘even’ extraction. Extracting less than this amount gives you an under-extracted brew, while extracting more gives you an over-exttacted brew. I’ll link to a post with more detail on this here when I’ve written it 🙂
How does Channelling Occur?
When we brew coffee we are always dealing with water (comment down bellow if you know of an exception).
Water obeys the rules of gravity: it will always seek to travel downwards AND it will always find the path of least resistance to do so.
When a bed of coffee grinds – whether in the puck, paper filter or in a filter basket of any kind – has air pockets, it is certain to channel to some degree.
A Channelled Extraction
So is a channelled shot (or filter) over or under extracted? Well both. Let me explain.
The coffee yield (end result: shot or brew) will be over-extracted. This is because the area of the coffee bed (where the air pocket is) has had water running through it extracting all the oils from the coffee grinds until there is almost none left: over-extraction.
At the same time though, the rest of the coffee grinds are not getting as much water as the area with the air pocket and is having far less water extracting the oils. Therefore the coffee as a whole will be under extracted.
Hopefully I’ve explained that channelling is not something we want to have during our brew. So how do we stop it from happening?
Dosing: During the grinding process make sure that the coffee grounds are evenly distributed in the puck, areas of the puck that are less dense in grinds will be weaker and water will run through there more.
Collapsing: After the dosing there will be a mound of coffee in the puck, tap the portafilter gently to colaspe the mound. Too hard if a tap will create cracks that the water will run through without extracting much of the oils.
Tamping: Tamp straight with an even pressure, check to make sure it’s level, water travels downhill and will do the same in your puck. Also don’t whack on the sides of the puck before or after tamping, it only disturbs the coffee bed and will create air pockets.
Pulling the Shot: Be consisting in pulling your shot. Don’t start and stop the flow of water, already wet grounds are softer and water will channel through it.
Coffee Bed: Make sure the coffee grinds are evenly distributed and that there are no cracks or fault lines in the coffee bed.
Water pour: If you’re using a manual method of filter coffee, be sure to evenly wet the coffee grounds during the brew, don’t stick to one area. Also be gentle with your pour, a rough pour will disturb the bed too much.
I hope this has been helpful for those reading, comment down below if you have any useful tips that I missed or any relevant informatio that can bring further discussion and discovery. Thanks!