Wow, there’s been awesome response to my previous post on pulse brewing and a couple great questions/points have been brought up. There are three that I would like to address over the next few posts. First, pulse brewing for pour over methods like the Kalita Wave and Gino. Second, should a barista pull the filter off a Chemex or Hario at the end of the pour over before letting the water drain into the cup. Finally, the migration of coffee particles and how this impacts water flow. I will give fair warning, this post will be a little more intense on the coffee geek scale than the last.
1. Kalita Wave & Pulse Pouring
I will confess, I have never used a Kalita Wave. Fortunately, I have been able to observe this brew method over the past few weeks since the “Taste is King” pour over competition (we won’t discuss my performance, but let’s just say I’m a lot better at math). Let’s compare a Chemex to a Kalita Wave:
It’s obvious that the Wave is much shorter than the Chemex. Also, the Wave has a flat bottom with three holes to allow coffee drain into the cup and the Chemex is conic and has one point of drainage at the bottom. With the Chemex, water flows through the coffee bed and is prohibited from moving sideways by the glass wall that the filter is sealed to. Therefore, it can only flow downward and eventually leave the coffee bed through the filter at the bottom. Although not in the picture, the Wave has a wavy filter (Kalita’s marketing department is the pinnacle of originality) and this filter permits the sideways flow of water. Well, who cares whether water can move sideways or not? The big difference is that the Wave controls flow rate (remember Q?) by the limiting the size of the holes at the bottom of the dripper—whereas the Chemex filter controls flow in the Chemex. Let’s detour really quick to one of the equations that describes the flow of liquids:
Q (Flow Rate) = A (Area) x V (Velocity)
It’s getting intense, but the best way to think about this is to remember spraying someone with a water hose. Hoses are pretty pathetic by themselves if you want to win a water fight, but slightly plug the end with your thumb and BAM! Instant, unending watery doom for your competitors. Why is this? Well, flow rate must always remain the same in the above equation, but you’ve just decreased the area the water can flow through, so to balance the equation the velocity must increase. Therefore, giving you much more range and intensity with your hose.
Back to sideways flow, since the Wave allows this, the flow is not governed by the filter. Therefore, I theorize that coffee extraction is not significantly dependent on height of the water column (hydraulic head) in the filter, but is instead dependent on the velocity of the water passing over the coffee grounds, which is why the Kalita Wave must be pulse brewed. As an illustration, another one of my awe-inspiring iPad drawings.
As water is introduced to the Kalita Wave, it hits the grounds and disperses in all directions. I believe it is a combination of the water temperature and the speed at which the water passes over the coffee grounds that ultimately determines the overall coffee extraction. This is why pulsing is required, because if a continuous pour is done, the water’s velocity essentially becomes zero as soon as it hits the standing water in the Wave and yields an undesirable cup of coffee.
So, unlike the Chemex and Hario V60—in which extraction (I believe) is governed significantly by the hydraulic head—the Kalita Wave’s (and similar methods) extraction is governed by the pulsing and temperature of the water. I’m hoping to provide experimental evidence for these theories in the future by using some of the equipment available to me at the University of Cincinnati, so be looking for that in the coming months. In the mean time, keep making fantastic coffee and let me know your own experiences with your pour overs and if you think I’m completely nuts (truthfully, I am always open to correction)!