Well, okay, maybe not meaningless.
I have been doing some thinking and experimenting, lately, and it led me in a surprising direction.
Everyone knows the dogma. You adjust the grind and dose to achieve a shot that blondes at 25-30 seconds. A finer grind leads to a darker, more concentrated extraction with a dramatic blonding point: a ristretto shot. A coarser grind gives a larger volume and a more honey-colored shot with a subtler blonding point, probably because the dark colored coffee solutes are dispersed in a larger volume.
Then one day I had a coffee that seemed to be incomplete at the endpoint. Now, I have gone through and tasted small fractions of the shot throughout its progression. I have also purposely omitted the beginning fraction, pulled center cut shots, and ended shots progressively early -- all this to get a sense of what different parts of the espresso shot contribute to its overall character.
It's no surprise that the beginning and ending fractions need to balance each other out, with sour and bitter sort of canceling each other to make a sweet shot. What was surprising was that one day I had a coffee that blonded at 25 seconds but which seemed like I had cut it off too soon. Exploring the extraction space, moving the temperature, shifting from a ristretto to a lungo: none of this was exactly satisfactory.
This made me think about what happens as an extraction progresses: the volume increases, the solute load is dynamically changing, and the pH is gradually moving. At a certain point the dark-colored solutes are thoroughly washed from the coffee grounds in the basket: the blonding point.
However, if you have ever done a chemical extraction, you know that you don't just pay attention to the obvious precipitate. It may be an impurity, it may not have the same pKa as the molecule you are trying to isolate, etc. Now, given that an aqueous extraction of coffee is fairly invariate, BUT just like an Ethiopian Harrar doesn't taste like a Panama Esmeralda, there are going to be some differences.
So, I tried going a little further: 1...2...3... finally 5 seconds past the blonding point where I would have stopped. And the cup finally became complete, the espresso was sweet and balanced. Going back and looking at the weight of the coffee grounds and the weight of the final extraction reveals a correlation to brew ratio paradigms that support the concept of using volumetric dosing versus time or blonding point as and end point of the extraction.
And, yes, I know it has been discussed previously, albeit perhaps, obliquely. I thought I would see what other people thought of this more pointed attack on the paradigm. I suggest that while the blonding point may be a good starting point, it may require additional adjustment to find the correct ending point for a particular blend of coffee beans.
Or do we need to go further and dispense with the blonding point, focusing instead on volumetric dosing, measuring weights and brew ratios?