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Percolation Mechanics

P 1.03 Grinding Fresh

Grinding Fresh

The importance of grinding fresh is emphasised by the volatile nature of the aromatic gases trapped inside the coffee beans. All aromatic gases are volatileVolatile aromatic gases, by definition, have a low boiling point. Even if we are able to dissolve them into the water, many of them are likely to evolve (un-dissolve) out of our coffee brew right under our noses. This occurs, as we are brewing the coffee, as the temperature of the slurry (the mixture of coffee grinds and water) begins to decline.

The mechanics you need on-bar to deliver your customers as much aromatic intensity as possible must involve reducing the time between grinding and brewing — the less time the better. The grinder should be positioned on or near your brewing area, and the workflow should involve grinding and levelling the coffee bed as the last steps in your preparation before pouring commences.

An established system of measuring a decline in coffee freshness records the weight loss of coffee over time. Roasting gasses trapped inside coffee beans can account for up to 2% of the weight of a coffee bean. Over the course of approximately 100 days, the majority of this gas escapes. Approximately 87% of this amount is carbon dioxide, 7.3% is carbon monoxide and 5.3% is nitrogen gas (Illy, E. & Navarini, L. Food Biophysics, 2011). None of these are aromatic. Aromatics total less than 0.4% of the total gas content of roasted coffee.

In the BH Advanced Coffee Making course, we conducted an experiment using an extremely precise laboratory scale. We measured a 0.29% total weight loss of a measured dose of coffee, 1 minute after grinding it. This amounts to almost 20% of the total gas content of a typical roast. The message to take away here is that we should endeavour to prevent as much aroma loss as we can by reducing the time between grinding and pouring.


Understanding Grind Retention

All grinder designs take a little time to dispense the coffee they have ground.