Espresso Puck Physics.. What Really happens?

Before I begin, I would like to say that this is in no way to be taken as anything conclusive, or as an "article" of sorts, but rather as more of a mode of thinking in text format.

I could be right, I could be close, or I could be in the wrong ballpark entirely.

I recently read that there is somewhere in the neighborhood of 540 pounds of pressure constantly pressing down on the bed of coffee in the portafilter during the 9bar extraction. What is this concept of extraction, really? Does the water absorb more solubles under the high pressure and high heat? Does the puck really SWELL under the weight of 540 pounds of water?

Honestly, I really think not. What does this say about pre-infusion? Does pre-infusion really "set" the puck to swell so it provides a more evenly distributed bed of coffee? Or does the pre-infusion force the puck to become wet more thoroughly and evenly throughout? Afer-all, "water is lazy". Water will go where water already is.

Additionally, does proportionally more water mean stronger extraction capabilities in the same pull? Why is it that more complexity is usually achieved from a lighter dose than that of a heavier dose with MORE coffee in the basket? Doesn't more coffee mean more coffee flavor?

Here's what I think. I think pre-infusion helps, not in that it swells the puck for an even extraction, but that it allows the water to find the niches and dense spots in the puck before the pressure hits at full force.

I think that the puck does not "swell" as a result of water contact. I think that the puck swells as a recoil from the pressure be forced upon it for 25-30 seconds. Under that kind of pressure, the cellular structure of the coffee particles have to be under some sort of tension, which would be released at once upon the release of pressure (a'la 3-way valve.. non-valve systems will react differently, I think).

So, we may have now established the physical shape behavior of the puck under pressure. What of the pressurized water's extraction properties?

It is my belief that rather than absorbing solubles, the highly pressurized water actually displaces many of the aromatic and flavor components within the bean structure. The high pressure forces them out.. the water does not extract, but rather pushes these components out of the cellular structure of the grind particles. A finer grind means more surface area which means more exposed components to be displaced. At the same time, this also means more resistance to the pressure, which results in a longer contact time.. resulting in components being absorbed, as well as displaced by the water. Too much contact time will result in flavor components most of us would really rather not have in our cup.

The combination of displaced solubles and absorbed solubles creates a balanced flavor. Too much of one or the other, and you end up with either a sour or bitter pull. Thankfully, much of this shift in "extracted" properties is easily seen with the naked eye.

It's not only about even pressure on (and within) the puck. It's also about even contact time with the coffee particles and the pressurized water. Dense spots will flow much more slowly than air pockets. Which brings me to my next, and final, idea.

At what point does the water become saturated with dissolved solids or solubles? Just like osmosis, less saturated water will absorb more quickly and readily than that of saturated water.

Enter: The science of the ristretto. Ristretto shots take more time. Sometimes a LOT more time. The result is a richer, more concentrated, lower volume shot of espresso. That is, the ratio of water to coffee is considerably reduced. There is no doubt that the longer contact time is absolutely essential to achieve such a result.

Here is where it gets interesting.

Wine tasters will swirl the wine in the glass to allow air to incorporate into the liquid, and "release aromatics" and allow the flavors to expand.

Beer afficionados will let a beer warm up to near, or at room temperature, and then pour it into a tapered glass that is wider on top to allow the flavors to expand.

What is the taste capacity of a single tastebud? Is it possible to cram too many flavor components into such a concentrated form that, while all flavor components are present, only a few are actually perceived by the taster?

Are the flavor components for a ristretto actually any different than those in an "under the line" normale, or are we just unable to perceive the dense culimnation of flavors in the ristretto when compared to the normale? Does the expansion of flavor components in the normale actually cause an increase in our ability to perceive more of the flavor components that are present in both, or is the coctail entirely different?

This thought process began last night. I couldn't wait to begin writing about it.

I'm sure there are many factors that a non-chemist and non-engineer and non-physicist like myself are not even aware of, but this still causes me to realize something on a very real and tangible level.

In the science and practice of espresso, we have such a very long way to go. We are nowhere near the pinnacle. On top of that, consider the science of coffee quality, and the concept of subjective opinion being brought into question by minds such as that of Jaime Van Schyndel.

Concepts and ideas such as these make me understand more and more how little we actually know. It makes me realize that we are still (after ~50 years) in the infancy of espresso theory.

I have not even begun to touch on the topic of tamping, polishing, how hard to tamp, temperature, etc.. etc.. So many factors.. so little comprehension in a single instance of time.

And now, to remind us of why we stress about these little details more than sanity would normally allow, a picture of some latte art at work earlier this evening.