I've been researching during this weekend for a "sort of" handy pour over coffee kettle. And it was rough. Even as a casual amateur, I found that almost all the product descriptions online are suspicious. By saying so I mean they always neglect the parameter I care most about--the spout diameter. Here is some personal opinions about pour over coffee kettles to share with hand-drip fans:
What, I think, are the actual important features? Body material, curve and diameter of the spout, and volume.
Hand dripping is a fun game of timing and thermal control. It's less perplexing than espresso-making (here I mean with semi-automatic or say semi-manual machine) because the pressure dimension is not in yet. Here I only want to discuss the brewing part, with a little attention to grinding, though bean-selection and roasting is the true foundation of all drinkable coffee (there is no salvation for any cup of coffee if either process gets screwed up).
There is NO real time control when you start pouring. The speed of dripping has already been determined by the properties of your filter, grinding and the beans you use. The size and charge of pores sets a time limit but not a critical one. You can figure when you prewet /warmup your drip-gears. It's usually pretty fast. Anyways, you don't have many options in the market. How deep your beans are roasted, how long since they were roasted and in what container they've been stored, also matter. You can tell the difference simply by smelling of it, the sound and touch if you're manually grinding it. It is also possible to visually see it when hot water makes its first contact with your coffee: fresh coffee absorbs more and therefore has larger volume change. Sometimes I like to have a 30 seconds prewet of the ground coffee before actual pouring. At this point you can actually measure the dV if you want. The actual fresh/dry-speed curve may not be that straight forward. I haven't read articles on this nor done systematic tests by myself, so you have to rely on our own observation for this part. The real time control is actually grinding. While consistency of particle size is fundamental to the body and flavor (and it depends on your budget...), grinder setting crucially determines dripping speed.
So the kettle doesn't control time, but a good kettle and a steady hand affect the time-thermal curve. You can end up with very different stuff in your cup depending on how you play this part. Of course, you have to first heat up the water but don't go beyond 95ºC (203ºF)... except you're pretty into the burnt flavor sometimes I encountered in Dunkin' Donuts...or below 85/185, especially when the dripping process is long so the temperature drop is huge at the end of it, the cup can end up too sour or tart (here I think is a subtle difference: tart is more likely to be a result of bad roasting or storage).
A good kettle helps you keep the temperature in range, as well as maintain a stable dropping rate over time. In other words, with it you gain CONTROL!
So what features of a good kettle will help you control?
Volume is the easiest to start with. I propose a pour-over kettle should not be less than 1 liter. You can go beyond that as much as you want, as long as you are able to hold and move the kettle fluently. Here I skip the lecture about the relationship of volume, surface area, heat exchange and temperature change, but the volume of the container give you a baseline temperature drop rate, and you don't want the curve to be to steep.
There is a little debate on the material part among we amateurs (don't know what professionals say about this). Some vote for bigger thermal capacity. I favor better thermal conductivity. This argument might be contingent on the specific kind of shape of kettle I preferred, which I'll mention later. The issue here is, even if the body is heated to 95º, the water temperature is in gradient along the spout. It drops even further when the stream goes through the air, hits the coffee and drips into a lower container eventually. There is a huge space for untenable variations. A kettle with good conductivity can help you as far as to the spout mouth. Imagine your first pour is only 80º which gradually changed to 95º then back to 83º -- I'd say this cup is basically ruined (it's the worst if you use a multiple-pour procedure as I do, so the thermal curve goes up and down several times--and that's part of the reason that I'm researching for a new one). The point is: the temperature is going to drop anyway, but you want it to drop consistently and at a stable rate.
And why does a kettle still matter beyond the physical boundary of the kettle? Because what you really want to control is the variation in the dripper! Two problems are involved here. One is the variation across time; the other is the variation within the dripper. The first one can be controlled by keeping the water level within a small range of change, and pour as continuously as possible. The key story behind this is that the temperature in the dripper drops way faster than in the kettle. That's why you don't pour in the volume you want all at once, otherwise whatever kettle you use is irrelevant. The best solution so far, I think, is the so-called "no-break" method: you pour at the same speed as it drips--but surely that's very hard to attain. The second one can be controlled through pouring in spiral circles. There is also a debate about clockwise circling or anticlockwise. Some Japanese coffee master argued something relevant to nuclei spinning....but I think the influence should negligible...The point is: you don't want to keep you stream at one spot resulting a inconsistent heat distribution, and hence uneven extraction.
How well the two solutions I mentioned works is the most tricky part of hand pour over, but also where all the fun is at. That all depends on how well you control your wrist and therefore the stream. And that further depends on the design of the kettle spout. You want your stream to be controllable from the very beginning of the pouring when the kettle is pretty full. At this point a small change in angle may produce a large change in the size of the stream. Taking the limited tension-sensor-motor sensitivity of human in to consideration, it means it would be hard to maintain the stream at the size as you want. You can definitely train yourself through lots of practice, or at the same time, get yourself a kettle with better spout design. My personal experience is... smaller diameter does help limiting your stream size, and a moderate-sloped long spout with a well-modeled tip will help you keep the spill smooth (kind of due to reduce the surface tension gap...).
But anyways, you'd wanna find a kettle that loves your own hand. Helping you go anywhere you want in a cup is the soul of a coffee kettle!
Munks.
19/8/12
