This week’s question grows out of last week’s post on defects. While the conversation ranged a wider scope on green and roasty topics, allow me to distill it to this: how can you tell the difference between grind/roast when it comes to over/under flavours?
This can be a challenge because they are interlocked. I am going to focus on espresso and omit key elements like burrs, dosage, temperature, pressure, and water chemistry (I can follow up on these in future dispatches, if people are curious). Let us start with dialing in a shot:
Finer grind setting
Fine grinds lead to an intensification of strength because you take more soluble flavours out of the coffee. Finer mean an increase in total time of extraction (until a point of diminishing returns, in which grinds will reduce time by blocking extractions with clumping and tiny particles). Grinding too fine means coffee is too strong and is over-extracted.
This is identified by: bitter, potent, overwhelming, sharp, severe, intense, and harsh flavours. Think kale stem, the membrane of green pepper, undercooked vegetables, cloves, peat or wood, tobacco, charred meat, the dry mouth-feel of campari, or the tannic bitterness of young wine. It is empty, hallow, and astringent, with no clearly defined sweet flavours. It can give the impression of roast.
Coarser grind setting
Going coarse reduces strength and extraction because you eliminate the amount of soluble flavours coming from the coffee. It will over-represent acidity relative to other flavours because they are more soluble than sugars. Courser grinds mean a decrease in total time of extraction, as the water flows freely through the larger particles. Grinding too course means coffee is too weak and under-extracted.
This is identified by: alkaline, sour, vegetal, salty, muted, sparse, nutty, papery and metallic flavours. Think citrus zest, IPA hops, granny smith apple, green strawberry, peanut skins, cilantro, Gose beer, salt and vinegar chips, parsley, and lemongrass. It has a very quick finish and disappears off the tongue quickly. It can give the impression of underdevelopment.
Ideal Extraction
A well-extracted coffee will taste sweet. It will have complex acidity reminiscent of ripe fruits that will be balanced to the other notes. Key markers are creamy, buttery, and smooth mouthfeel with a very, very long finish. An ideal extraction of a well-roasted coffee will mimic the notes and flavours of the cupping table.
Always Blame the Roaster
It is difficult to dial in a coffee that is underdeveloped because it will have a very low level of solubility. The chemistry varies coffee to coffee, but broadly: malliard reactions between amino acids and reducing sugars combine with caramalization to generate a huge number of flavour and aroma molecules. Hence, darker roasts increase the ratio of these reaction byproducts and make it easier to extract the volatile compounds.
Every roaster needs to make a decision of when to drop a batch. The line between under and over can be very slim (especially given its reliance on the inner bean) but essentially it requires developing coffee far enough to ensure solubility and a balance of flavours. As I have stated here in the past, the problem with going too far is rather than tasting origin, you taste the impact of the roast itself.
tl;dr
SO, how to tell the difference. If you are grinding increasingly fine but ending up with the green flavours associated to coarse above: the roast is likely under. If you are grinding progressively coarser but ending up with the char flavours linked to fine above: the coffee is roasty. Again, this is a potentially dangerous oversimplification because of the massive impact of burrs, dosage, temperature, pressure, and water chemistry but in my defense, I did just say to always blame the roaster.
The best advice for those hard to dial-in coffees is to do a cupping. Under and over notes cannot hide on the cupping table.
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Lee Knuttila 