Steering with the throttle

In the middle of an interesting phone conversation with Philip Search, I was trying to find an analogy to help explain a rather obscure aspect of espresso making. I hope it didn't throw him off too much when I came up with the following:

If you're ever done automobile racing, you've experienced the phenomenon of steering with the throttle. When you're in a curve, and your tires are working near their limit of adhesion, you can actually keep the steering wheel fixed and steer the car with the accelerator pedal. It is a revelation to experience this for the first time, because nothing in everyday driving tips you off that it might be possible.

By the way, please don't attempt to learn how to do this without an instructor on a track. Otherwise, you may experience more than you bargained for and, as they say in racing, fail to keep the shiny side up!

OK, so what does this have to do with coffee? Some time ago, I was experimenting with espressos, trying to figure out how preinfusion (or the lack of it) affected the extraction. And I stumbled upon something unexpected.

I had rigged up a series of valves that allowed me to flip back and forth between two extraction scenarios. In one, the initial flow of water to the group was restricted so that the buildup to full 9 bar pressure took about 7-8 seconds. In the other, the initial flow was unrestricted and it took only a second or two to get 9 bars. The difference was roughly like having installed an 0.6mm gicleur (slow buildup) and then switching to a 1.0mm or larger gicleur (fast buildup).

The surprise was that the fast pressure buildup had the same effect on shot timing as if I had used a much finer grind: the shot flowed so slowly from the portafilter that I had to grind more coarsely for subsequent shots. This was the opposite of what I had expected (which was that the faster pressure buildup would result in a shot that took less time).

At the time, Dr. John offered an explanation for why this occurred, and he's probably correct. But the bottom line is, not only does preinfusion lessen the chance that you'll have channeling in the portafilter, it also changes the grind required for your desired shot timing. Exactly how this affects the shot's flavor and texture is a vast subject....

I always thought this was pretty interesting; I hope you do, too. So, kids, be open to new phenomena, experiment with preinfusion in your espresso making, and always keep the shiny side up! :-)