Somebody please slap me in the face.
The "third wave" espresso world seems so strange: "temperature stability" has become religious dogma.
And common sense no longer accounts for much.
If you're wondering what the heck I'm talking about, I'll try and explain.
A decade or more ago David Schomer popularized a theory that described how an espresso machine should work. If you made a graph of the brew water temperature that the machine delivered, it was supposed to be "ruler flat" for the duration of a shot.
For David's blend, that meant the water temperature should rise as rapidly as possible to 203.5F, and remain there until the shot was finished. Other blends might have different optimum temperatures, or even several optimum temperatures, each expressing different qualities of flavor and texture. But it was a basic tenet in David's theory that the flat temp profile was necessary for the finest espresso.
Was this theory ever fairly tested? How did it become generally accepted? And how is it that the only machines acceptable for Barista Championships must perform this way?
In my opinion, the flat temperature theory, like the flat earth theory from centuries ago, doesn't bear close inspection. Here's why:
Coffee in the portafilter starts out slightly warmer than room temperature (it picks up a little heat in the grinding process). Even if you force water through it that is absolutely stable in temperature, the coffee in the middle and bottom of the puck gradually rises in temperature as the shot proceeds. It gets close to the temperature of the brew water, but never reaches it.
In other words, ESPRESSO IS NEVER EXTRACTED AT A STABLE TEMPERATURE, no matter what the brew water temperature does.
That's why insisting on ruler flat brew water temperature seems like a very peculiar requirement to make the finest espresso.
According to Michael Teahan, the Italians recognize this fact. Many Italian machine tuners prefer to start their brew water temperature very hot, gradually reducing it over the course of the extraction. This has the effect of getting the extraction environment in the basket up to temperature faster. But it still doesn't change the fact that, given the existing technology, IT IS IMPOSSIBLE TO EXTRACT ESPRESSO AT A STABLE TEMPERATURE.
But of course we all know that the Italians are backward buffoons, while we are cutting edge third wave baristas. Right? [please note, I'm being sarcastic here]
To be fair to David and his disciples, his theory has never been fairly tested because no one has an espresso machine that can accurately reproduce different brew temperature profiles. If an espresso machine could produce flat temperature profiles, rising temperature profiles, and falling temperature profiles at will, we'd be able to run some valuable experiments. Until then, we're stuck with comparing the espresso that comes from Synesso/GB5 machines (with their fairly flat profiles) to the espresso from heat exchanger machines (with their mostly falling profiles). But there are so many other variables (group and dispersion screen design, preinfusion scenarios, pressure variation, etc) that definitive conclusions are very difficult to come by.
In the absence of a technical breakthrough, many espresso machine designers have settled for a much less demanding requirement: they try and design their machines to reproduce the same temp profile with every shot. So whether you pull your shots one right after the other or a half hour apart, engineers nowadays take pains to make the machine deliver the same temperature profile each time. But this is a far cry from being able to tweak the temperature profile itself.
Hopefully more advanced machines will be introduced that will soon allow accurate temperature profile testing. Then will we replace conjecture and orthodoxy with actual experience. Until then, perhaps we should let the dogma out for a walk.
From Arlington, Virginia. Special Guest: The incomparable Ms. Liz Zamorski, General Manager, murky coffee capitol hill.
