Coffee flavor wheel: a milestone in global sensory science
1. The birth and significance of the SCA flavor wheel
Development background: Developed by the Specialty Coffee Association of America (SCA) and World Coffee Research, updated to the current version in 2016.
Core logic: Classify the 110 flavors that humans can perceive into 9 categories, and establish a sensory coordinate system from the center (basic taste) to the periphery (specific description).
Scientific basis: Based on 1,300+ volatile compounds detected by gas chromatography-mass spectrometry (GC-MS) technology, matching human sensory thresholds.
2. Analysis of the flavor wheel structure
First layer (core): basic classification (such as fruit, flower, sugar, nut/cocoa, spice, acid/fermentation, green plant, roasted taste, other defects).
Second layer: detailed descriptors (such as "fruit" is divided into berry, citrus, stone fruit).
Third layer (outermost layer): specific reference objects (such as "black currant" and "bergamot").
Chemical codes of 5 key odor types
1. Fruity
Chemical origin:
Esters (such as ethyl acetate): tropical fruit aroma (pineapple/mango).
Terpenes (limonene): citrus notes (orange/grapefruit).
Typical beans: Ethiopian Yirgacheffe (washed), Panama Gesha.
2. Nutty/Cocoa
Chemical origin:
Pyrazines (2-ethyl-3,5-dimethylpyrazine): roasted nut aroma (almond/hazelnut).
Furanone (maltol): milk chocolate sweetness.
Baking effect: medium-dark roasting (Agtron 55-65) is more obvious.
3. Floral
Chemical origin:
Phenylethanol: rose aroma (common in sun-dried beans).
Linalool: jasmine/lavender aroma (characteristic of washed Colombian beans).
Fragility: Light roasting has high retention and evaporates quickly within 15 minutes after grinding.
4. Fermented
Chemical origin:
Acetic acid: wine aroma/apple vinegar aroma (anaerobic fermented beans).
Butyric acid: cheese/yogurt flavor (defective when over-fermented).
Controllable application: Costa Rican black honey treatment (precise temperature control fermentation for 48 hours).
5. Earthy
Chemical origin:
Geosmin: wet soil smell (Sumatra wet planing method).
Pyrroles: humus texture (produced by old beans or improper storage).
Controversy: Mild earthy flavor increases complexity (such as Indonesian Mandheling), and excessive amount becomes musty.
Sensory tasting training: from laboratory to daily practice
1. Standardized cupping process (SCA protocol)
Grinding: 70%-75% of the particles pass through the US standard No. 20 sieve (coarse salt).
Smell the dry aroma: record the dry aroma before water injection (reflecting volatile esters).
Break the dregs and sniff: break the dregs 4 minutes after water injection, and quickly sniff to capture highly volatile substances.
Sipping: Use the "noodle sucking" method to atomize the coffee liquid to cover all taste buds on the tongue.
2. Olfactory memory library construction
Tools:
Le Nez du Café (coffee nose): 36 standard aroma bottles (such as "roasted almonds" and "black currant").
Homemade flavor packs: fresh fruit peels (orange/blueberry), spices (cardamom/cinnamon).
Training method:
Daily blind smell test (5 minutes), record associative words.
Compare the aroma differences of the same bean variety with different roasting degrees (light/medium/dark).
3. Taste map calibration
Acidity sensitivity: Test the perception threshold with citric acid (0.1%-0.3% solution).
Bitterness balance: Compare the bitterness levels of quinine (10-100ppm) and coffee.
Sweetness capture: Identify the residual sucrose (0.5%-2% concentration) in the aftertaste.
Why do different people taste different flavors from the same bean?
Genetic differences: OR6A2 gene determines sensitivity to aldehydes (floral scent), and 25% of the population cannot perceive jasmine scent.
How to distinguish "fermentation aroma" from "fermentation defects"?
Time control: High-quality fermentation (such as 72-hour water washing in Kenya) has a red wine aroma; over-fermentation (>120 hours) produces a rancid smell.
Does the earthy smell mean that the coffee is of poor quality?
Not absolutely. The earthy smell of Indonesian wet-hulled Mandheling is a sign of its style, but it must be strictly distinguished from the musty smell (improper storage).