The dominant alkaloid in Coffea arabica (0.8–1.4% dry weight) and C. canephora/Robusta (1.7–4.0%). Acts as adenosine receptor antagonist (A1, A2A), producing central nervous system stimulation. Thermally stable up to ~235°C — survives roasting intact. Contributes 10–30% of perceived bitterness. Biosynthesised from xanthosine via a 4-step enzymatic pathway in leaf and seed.

Present at ~0.05–0.18% in green arabica. A caffeine metabolite and biosynthetic precursor. Milder CNS stimulant than caffeine, stronger cardiovascular activity. Contributes smooth bitterness often described as cocoa-like. Higher concentrations in natural-process coffees due to fermentation dynamics.

Trace levels in coffee (0.001–0.002%). Strong bronchodilator. Used clinically for asthma treatment at therapeutic doses. A minor caffeine demethylation product. Historically significant in tea; in coffee, primarily notable as a bioactive metabolite of caffeine catabolism during digestion.

Present at 0.5–1.0% in green beans. Highly heat-labile — degrades extensively during roasting to pyridines (roasty/earthy aroma), nicotinic acid (niacin/Vitamin B₃), and other volatile compounds. A key precursor to roast flavour development. Inversely correlated with roast degree — light roasts retain more. Implicated in antidiabetic and neuroprotective bioactivity.

The dominant CGA isomer. Forms from esterification of caffeic acid and quinic acid. On roasting, degrades to quinic acid + caffeic acid, and further to catechols, phenols and volatile phenols (guaiacol, 4-vinylguaiacol). Primary driver of coffee’s antioxidant capacity. In Kenya AA green beans: 6–9% dry weight.

Esters of ferulic acid and quinic acid. Present at ~0.5–1.0% in green beans. Contribute smoky/spicy volatile phenols (4-vinylguaiacol, vanillin) during roasting. Ferulic acid released during roasting is a key precursor to vanillin — responsible for subtle vanilla notes in medium roasts.

Two caffeic acid residues esterified to quinic acid. Collectively 0.7–1.5% of green bean dry weight. More bitter than mono-esters. Higher in robusta. Important antioxidants — strong DPPH radical scavenging activity. Robusta’s higher di-CQA content contributes to harsher bitterness vs arabica’s cleaner profile.

The least abundant CGA subclass (~0.1–0.3%). Esters of p-coumaric acid and quinic acid. On roasting, yield p-coumaric acid which decarboxylates to 4-vinylphenol — a phenolic compound with spicy/clove-like aroma. More important at trace levels as aromatic contributors than for raw antioxidant load.

Dark-brown nitrogen-containing polymers formed at the terminus of the Maillard reaction. Constitute 25–30% of roasted coffee dry weight. Primary drivers of coffee’s brown colour and body/mouthfeel. Demonstrate significant antioxidant activity in vivo — scavenge reactive oxygen species. Also exhibit prebiotic activity, stimulating beneficial gut microbiota. Their structures remain incompletely characterised — a frontier of coffee science.

One of the most abundant volatile compounds in roasted coffee. Forms from pentose sugar degradation via the Maillard pathway. Aroma: sweet, caramel, roasty at low concentrations; sulfurous at high. Reacts with hydrogen sulfide to form 2-furfurylthiol (FFT) — the compound primarily responsible for the iconic “roasted coffee” smell at ppb levels.

Formed from Strecker degradation of amino acids combined with reactive carbonyl compounds. Over 80 pyrazine derivatives identified in coffee. Key members: 2-methylpyrazine (nutty), 2,3-dimethylpyrazine (earthy/roasty), 2,5-dimethylpyrazine (popcorn). Concentration increases with roast degree — characteristic of dark roasts. Low odour thresholds — detectable at 1–5 ppb.

Formed from thermal degradation of feruloylquinic acids and lignin. Characteristic aroma: smoke, spice, medicinal. Important quality marker — moderate levels desirable; excessive guaiacol indicates over-roasting or robusta-heavy blends. 4-Ethylguaiacol contributes spicy/clove character. Detection threshold ~3 ppb in water.

The most potent cholesterol-raising compound in the human diet. Present in unfiltered coffees (French press, espresso, boiled coffee) at 2–4 mg/cup. Acts by antagonising the FXR (farnesoid X receptor), suppressing bile acid synthesis genes and increasing LDL-cholesterol. Paper-filtered drip coffee retains <0.1 mg/cup. Simultaneously exhibits anti-inflammatory and hepatoprotective effects at low doses.

Structurally similar to cafestol but with an additional double bond. Exclusive to Coffea arabica — virtually absent in robusta, making it a botanical authentication marker. Also a serum cholesterol elevator when unfiltered. However, demonstrates potent antiangiogenic properties in cancer research — inhibits growth of new blood vessels feeding tumours. Present as a palmitate ester in coffee oil.

Coffee beans contain 10–17% total lipids (arabica) vs 7–10% (robusta). Predominantly linoleic acid (41%), palmitic acid (32%), oleic acid (8%), stearic acid (7%). Coffee oil is concentrated in the endosperm. During espresso extraction, fine particles and emulsification generate crema — the oil-water-CO₂ emulsion atop the shot. Oil oxidation (rancidity) is the primary driver of stale coffee aroma.

Formed from trigonelline during roasting. NMP and N-alkanoyl-5-hydroxytryptamides (C5HT) are implicated in stomach acid secretion stimulation — relevant to coffee-related gastric discomfort in sensitive individuals. C5HT also suppresses acid secretion via a different mechanism. Dark roast coffees are paradoxically better tolerated by some acid-sensitive drinkers due to increased NMP, which inhibits proton pump activity.

The single most impactful aroma compound in roasted coffee. Detection threshold: 0.01 ppb (water). Aroma: roasted coffee, sulfurous. OAV in freshly roasted coffee: 10,000–50,000. Forms from reaction of furfuryl alcohol with H₂S during roasting (Maillard pathway). Extremely labile — oxidises rapidly post-roast. Primary driver of staling in ground coffee. Kenya coffees with higher acidity show slower FFT oxidation due to pH buffering.

Sulfur-containing compounds form the “dark underbelly” of coffee aroma — at very low levels they add complexity; elevated levels signal defect. Methanethiol (cabbage/sulfurous) from methionine degradation. Dimethyl disulfide (onion, roasted meat) — fermentation and roasting origin. Quality control: elevated sulfur volatiles indicate over-fermentation, robusta adulteration, or storage defect.

Aroma: caramel, sweet, almond-like. Formed from pentose sugars (arabinose, xylose) via Maillard reaction at 180–200°C. OAV ~100–500. Along with furfuryl alcohol and 2-acetylfuran, contributes to the “sweet-roasty” aroma dimension characteristic of well-developed medium-roast arabicas. Higher in washed arabicas vs naturals due to cleaner sugar profile.

Aroma: clove, spice, smoke. OAV: 500–2,000. Formed by decarboxylation of ferulic acid (released from feruloylquinic acid hydrolysis) during roasting. Especially prominent in lightly roasted Ethiopian and Kenyan coffees. A key discriminating compound between arabica and robusta — arabica produces higher 4-VG due to higher feruloylquinic acid content.

Aroma: vanilla, sweet, creamy. OAV in coffee: 10–100. Derived from ferulic acid via demethylation or directly from lignin degradation. More prominent in medium roasts — destroyed at higher temperatures. Contributes to perceived sweetness without sugar. Elevated in aged green coffees (enzymatic conversion from ferulic acid). A sought-after quality attribute in specialty arabica.

Lactones form from fatty acid cyclisation during roasting. γ-Butyrolactone: sweet, caramel, milky. δ-Valerolactone: coconut, sweet. Critical to the sweetness dimension in cupping — arabica coffees score higher “sweetness” partly due to higher lactone content vs robusta. Elevated in natural and honey-processed coffees due to lipid-rich mucilage retention.

The most abundant free amino acids in green coffee (30–40% of free AA pool). Asparagine is the primary acrylamide precursor — reacts with reducing sugars at >120°C to form acrylamide (a probable carcinogen). Regulatory bodies (EU, FDA) have established mitigation guidelines for coffee. Glutamic acid contributes umami character. Strecker degradation of these acids generates acetaldehyde, methylglyoxal.

Lysine’s ε-amino group is particularly reactive in Maillard — forms Amadori compounds efficiently. Proline and hydroxyproline (from coffee’s structural proteins) generate pyrroles — key contributors to roasty, bread-like aromatics. Arginine → via Strecker → 2-methylpropanal (malty). The relative ratio of basic to acidic amino acids varies with cultivar, soil nutrition, and processing method.

Although present at trace levels (0.1–0.5% of AA pool), sulfur amino acids are disproportionately important to aroma. Cysteine is the primary precursor to H₂S and sulfur volatiles including 2-furfurylthiol (the dominant coffee odorant). Methionine → methanethiol, dimethyl sulfide. Strecker degradation of methionine → methional (cooked potato — defect at high levels). Quality breeding programs for Kenya SL varieties select for optimal sulfur AA content.

A non-protein amino acid produced during fermentation (wet processing) and anaerobic conditions. GABA is a neurotransmitter associated with relaxation — its presence in processed beans reflects fermentation microbiome activity. Elevated GABA in honey/natural processed Kenya coffees is an active research area. Also produced under hypoxic stress in the living coffee cherry. Some specialty producers are deliberately enhancing GABA through controlled anaerobic fermentation.

Gold standard for quantification of chlorogenic acids, caffeine, trigonelline, sucrose, organic acids, and diterpenes in coffee. Reverse-phase C18 columns with UV/DAD or MS detection. Enables authentication (arabica vs robusta), roast degree estimation (CGA:caffeine ratio), and adulteration detection. Required for regulatory compliance (acrylamide, pesticide residue analysis).

Essential for volatile compound profiling and off-flavour analysis. GC-MS identifies and quantifies 800+ roast volatiles including thiols, pyrazines, furans, phenols, aldehydes. GC-Olfactometry (GC-O) pairs chromatography with human odour detection — identifies which compounds are actually sensorially relevant (high OAV). Used in Kenya to map terroir-specific aroma fingerprints and detect fermentation defects (butyric, isovaleric acids).

Rapid, non-destructive screening technology increasingly adopted by Kenya’s coffee cooperative factories. NIR predicts moisture content, caffeine, sucrose, CGA, and roast degree from spectral fingerprints in seconds. Machine learning models trained on Kenyan coffee datasets enable real-time quality sorting — replacing time-consuming wet chemistry for routine QC. Portable NIR devices now used at cherry intake stations.

Digital refractometers (VST, Atago) measure Total Dissolved Solids in brewed coffee (°Brix → % TDS). Combined with brew ratio, calculates Extraction Yield (EY%). SCA targets: TDS 1.15–1.45%, EY 18–22%. Under-extracted: sour, thin (low EY). Over-extracted: bitter, astringent (high EY). For Kenya’s complex acid profile, the sweet spot is often 19–21% EY at 1.30–1.40% TDS — balancing acid brightness without excessive bitterness.