#11 Don't Bother Making Your Bed
This blog isn’t so much proposing solutions but is more examining aspects of the filter coffee brewing we do in manual brewers, principally two areas I find nonsensical to good coffee making in V60’s.
I’m talking about beds: The post brew- wet coffee, or slurry left behind after making a conical filter brew. After a filter brew made in brewing cones such as a v60 it is a popular common practice on the final pour of water to settle the wet coffee bed with a gentle shake to flatten the surface of the brew. When the final water drips out of the bed we are left with a very flat bed of spent coffee grounds.
What’s the problem here? Generally its accepted that a flat bed of coffee grounds has had an even extraction of coffee throughout the brew because the bed itself is literally flat and even. While the surface of the brew is indeed neat and orderly, the shape of the v60 cone itself is deeper in the middle. This means that no matter how flat the surface is coffee grounds in the middle of the cone are at a greater density than grinds around the outside. These centre grinds will have a significantly longer contact time with the hot water throughout the brew.
Another more serious aspect of over extraction is fines migration. That is the act of ultra fine coffee particles sinking to the bottom of the v60 within the brewing phase. As the hot water poured over the bed draws them as low as possible in the cone they will, over the course of the brew, actually reorganise themselves. Leaving larger grind particles unable to slip around the smaller ones. This means our final slurry is rearranged coarsest to finest.
Every grinder creates a range of particles of differing sizes, the finest particles it creates are referred to as the fines. Because of their smaller size they will reach a total saturation (total extraction) before the bigger particles. Even if there was a filter brewer that could guarantee an even amount of water to every particle the fines would reach total extraction before the largest particles. If there is enough fines they will ruin the brew by causing uneven extraction within the bed- muddying the flavours present in the finished cup.
Frustratingly because the coarsest particles are always left at the upper reaches of the V60 cone the fine particles are being given more contact time with the water!
I guess the conclusion here is that a focus on flat beds is a focus on the coffee that is least likely to ruin your brew with over extraction. Adding to this, I think too much agitation of the coffee slurry during the brewing process will also move the fines around unnecessarily after they settle. It is in your best interests to just allow these fines to settle into place and then not constantly swirl in the turbulence of the brewing process. Anything aimed at creating a flat bed at the end of the brew via application of aggressive swirling either by hand shaking or by dipping into the brew* with aggressively turbulent pours will again assist in over extraction, a poor outcome.
Manually tapping especially has been shown to introduce a thin stream along the walls of the dripper that can either make channels** in the slurry or allow particles small enough to slip downward with water pressure to reassert themselves at the lowest points in the v60 cone***. Considering there will always be a fair amount of fines migration in any given filter coffee brewer we see an example of a method with the intention of flattening a bed to create even extraction introducing points for increasing extraction again later in the brewing cycle. A sure way of over extracting coffee particles of a certain smaller size while again doing little to extract particles that are larger.
Disclaimer, I’m warning against putting too much onus on flattening out the brew bed at the end of a brew. I however am not saying there should not be a certain amount of care taken to avoid the process of high and dry. A process where because of larger pulses of water at the onset of a brew we see coffee particles that end up riding high on the sides of the cone dripper prior to the end of the brew. These dried grinds are effectively taken out of the extraction process for the remainder of the brew, not extracting their quota to the end cup. Worst case scenario is a brew that is weaker than the initial aim because not enough grind contributed to the end result. For example a 12gram coffee to 200ml of water brew aiming for a 3 minute brew time that lost around 2 grams of grinds to the edge of the cone in the first minute has effectively lost 16% of its total soluble material for almost 66% of the total brew time. High and dry is avoided by making sure all the coffee is being constantly worked into the hot water throughout the brewing process. This will contribute to a nice even looking bed inevitably but is in itself not a reason to focus on the result of a flat bed per se.
A final point in handling fines is in understanding that the point at which the most extraction can be achieved is the earlier stages of the brew. One must approach the end of the brew with a gentler touch as this is the time where some parts of our coffee bed are reaching the end of their extraction potential- at least in regards to total extraction of favourable compounds. When I see ideas expounded online claiming to indicate favourable outcomes in brews based on visual indicators such as aiming for flat beds to get consistent evenness in cup extraction I am always cautious about their actual usefulness.
Always bring the filter brewing back to its most basic premise: we have a soluble material we need to become solute in water in a way that creates a favourable beverage as an end result. If the physics of beds, pours, kettles and so on don’t stack up no amount of exposition will change this. At the end of the day its just coffee and water doing what they can, if they can.
*this does not include any manual (paddle) agitation in the bloom: the first pour of a V60.
**Channels: a seam of weaker than average resistance in the coffee bed that water finds easier to flow through. Any coffee around the channel will show higher extraction than other denser areas of the bed due to higher levels of water choosing this easy way through the coffee slurry.
***reference Jonathan Gagne. The physics of filter coffee 2020 Jonathan Gagne. PG 103. Paragraph 4.