Which Came First, The Grind Size Or The Compounds?
Read on to hear why I think we’re asking the wrong questions when it comes to solubility
In my experiences, many baristas readily judge coffee quality based on arbitrary data of an extraction without a thorough grasp on the nature of solubility itself. Interpretations of the meaning and the applications of solubility are scattered far and wide in our industry.
Current Common Practice
Common practice of measuring extraction percentages has unarguably provided valuable insight into coffee quality. The current approach, which has been spearheaded by the likes of Matt Perger and Maxwell Colonna-Dashwood, now emphasises both the evenness of our methods and the perpetual search for optimally even extraction conditions.
One significant discussion for example, which typifies this approach is concerned with the subjective nature of brew strength preference. This is evidenced by the ongoing developments of speciality coffee capsules.
Increasingly baristas, who are familiar with standardised brewing control charts, are becoming aware of the inadequacies in solubility data’s application to sensory understanding. The more we understand, it seems, the more aware of our own subjectivity we become. As a result, the scope of our objective tolerance expands with greater acceptance of varying contexts.
Good friend, Mat North, put it succinctly recently when he wrote, ‘It’s not how much extraction that counts. It’s what it’s made of.
If Solubility interpretations are continually evolving, then what is next?
Mat’s comment mirrors my own views on the need to understand the chemical composition of the beverage, or unlock its ‘genetic code’. Much definitive research is available, and ongoing into the structure of green and roasted coffee, but there are still missing links. We have a reasonably obscured understanding, for example, of the interaction between ground coffee, solubility and the cup.
I regularly see that working baristas’ interpretation of changing grind size is based on an idea that all particle sizes constitute a similar make up of soluble compounds. What follows is an assumption that the discrepancies in particle-size distribution mean smaller particles are more readily extracted than bigger particles.
I propose that the pertinent question now should be, not the extraction value itself, but what it is constituted by. Furthermore, how this is influenced by grind size and whether, in fact, certain compounds have a tendency to always produce similar particle sizes when ground.
In other words, can particle size actually be defined by the compounds which exist in the coffee?
How can we test this?
Chemical compounds or compound groups existing in coffee have a tendency to always produce a specific particle size, therefore providing a soluble make up of significantly different material grind-to-grind.
The objective of testing here is to take a step forward in quantifying the complexities of sensory experience in coffee.
This concept looks primarily at how coffee behaves when it is ground, and the notion that different chemical compositions will result in significantly varied particle sizes. To test this we will be using Liquid and Gas Chromatography - Mass Spectrometry*
Fixed variables of coffee and water will be tested across a range of 10 micron sizes and each brewed to the following parameters:
- Set extraction percentage in non-espresso brewing environment
- Set brew strength in non-espresso brewing environment
- Set extraction percentage in espresso brewing environment
- Set brew strength in espresso brewing environment
The study of volatile aromatics in coffee and their compound groups has been explored in great depth, yet the results give us little indication into the characteristics of the final beverage. The loss of volatile groups as a result of grinding coffee will however hold clues in defining our own results here.
Using this method we will be able to analyse chemical compounds present, or absent, in coffee of different particle size sets and compare any discrepancies.
Compounds we’ll specifically be looking for will be those within the large compound groups of:
- Chlorogenic acids
- Hydroxyl acid groups
- Carbohydrates and low molecular weight sugar byproducts
- Proteins and amino acids
- Oils and fatty acids
Full parameters of the testing will be defined and released closer to the date and testing will commence in April.
The search for more meaningful understanding of solubility and its applications evolves perpetually. My hope is that this will contribute towards the collective progression.
For further reading on grinding and its implications keep an eye out for a recently completed paper by, among others, Christopher Hendon, Maxwell and Lesley Colonna-Dashwood, Matt Perger, Christian Klatt and Stephen Leighton.
* Liquid chromatography–mass spectrometry (LC-MS, or alternatively HPLC-MS) is an analytical chemistry technique that combines the physical separation capabilities of high-performance liquid chromatography (or HPLC) with the mass analysis capabilities of mass spectrometry (MS).