tags: [] - coffee/roasting - coffee/roasting/chemistry aliases: - Roasting and coffee acidity - How roasting affects acids

Acids in Roasting¶

Tags: #coffee/roasting #coffee/roasting/chemistry Aliases: Roasting and coffee acidity, How roasting affects acids Related: Roasting MOC | Quinides | Maillard Reaction | Development Phase | Coffee Chemistry MOC Status: ✅ Complete

Overview¶

The acid composition of coffee is profoundly altered by the roasting process. Green coffee contains a complex mixture of organic acids — primarily chlorogenic acids, quinic acid, citric acid, malic acid, and smaller amounts of acetic, lactic, phosphoric, and other acids. During roasting, some of these acids degrade, new acids are formed through pyrolysis and Maillard reactions, and the relative balance of acid types shifts significantly with roast level. The perceived acidity and specific acid character of the cup — whether it is bright and clean (citric, malic) or mellow and round (lactic, phosphoric) or harsh (acetic, quinic at high concentrations) — is determined both by the origin's inherent acid composition and by how roasting transforms it.

Acids in Green Coffee¶

The major acid classes in green Arabica:

Acid	Content in green Arabica	Character
Chlorogenic acids (total)	6–12% dry weight	Astringent, complex; primary phenolic antioxidant
Quinic acid	0.5–1.5%	Slightly sour, dry; major Maillard/CGA degradation product
Citric acid	0.3–0.6%	Bright, clean, citrus acidity
Malic acid	0.3–0.5%	Apple, soft, smooth acidity
Acetic acid	0.1–0.5%	Vinegary; formed during fermentation (natural/honey process)
Phosphoric acid	0.1–0.3%	Sharp, bright; responsible for the distinctive acidity of Kenyan coffee
Lactic acid	trace–0.3%	Soft, creamy; formed during fermentation; also some Maillard formation

How Roasting Transforms Acids¶

Chlorogenic acid degradation: The major acid change during roasting. Chlorogenic acids degrade extensively above 180°C: - At City+ / Full City: 50–70% of green coffee chlorogenic acid content has been degraded - Degradation products include caffeic acid, quinic acid, and quinides (see Quinides) - Quinic acid accumulates significantly at medium-dark roast levels; at very high concentrations (dark roasts) it contributes a dry, harsh sour note

Citric and malic acid degradation: Both degrade progressively with increasing roast level: - Light roasts preserve more citric and malic acid → brighter, clean acidity - Dark roasts have significantly reduced citric and malic → muted, round, less bright acidity - This is the primary chemical explanation for why light roasts taste more acidic than dark roasts

Formation of new acids during roasting: - Acetic acid: Formed through pyrolysis of carbohydrates above 200°C; contributes at high concentrations to sharp, vinegary notes in dark roasts - Formic acid: Small amounts formed through degradation of sugars and chlorogenic acids - Lactic acid: Minor amounts formed through Maillard-related pathways at moderate roast levels

Net acid content change: Total titratable acidity peaks at light-to-medium roast levels (City to City+) — the Maillard acids formed partially compensate for the degradation of chlorogenic and organic acids. At very dark roast levels, total titratable acidity falls significantly.

Perceived Acidity vs. Measured Acidity¶

Perceived acidity in the cup is not identical to measured titratable acidity or pH: - The nature of the acids (their pKa values, concentration thresholds) determines how acidic a coffee tastes - Phosphoric acid (prominent in Kenyan SL28) is perceived as particularly bright and sharp at low concentrations - Quinic acid is perceived as dry and harsh at high concentrations (dark roasting) - Malic and citric acids are perceived as clean and pleasant across a wide range of concentrations - Chlorogenic acids contribute astringency at high concentrations (light roasts) rather than simple sourness

Roast Level and Acid Profile¶

Roast level	Dominant perceived acids	Cup character
Very light (Cinnamon)	Chlorogenic (astringent), citric, malic	Sharp, astringent, insufficient sweetness
Light (City)	Citric, malic, phosphoric, some chlorogenic	Bright, clean, complex acidity
Light-medium (City+)	Citric, malic, some quinic	Balanced brightness; most chlorogenic degraded
Medium (Full City)	Malic, quinic; citric reduced	Softer acidity; chocolate and caramel dominant
Dark (Vienna+)	Quinic, acetic; citric/malic minimal	Dry, harsh, round; acidity perceived as bitterness

Key Facts¶

Chlorogenic acids (6–12% of green bean dry weight) are the dominant acid; 50–70% degrades by Full City roast level
Citric and malic acids degrade progressively with roast level; light roasts taste brighter because more of these clean acids are preserved
New acids (quinic from CGA degradation, acetic from pyrolysis) form during roasting; quinic contributes dryness and harshness at high concentrations
Perceived acidity peaks at City to City+ level — the balance of clean organic acids and sweetness is optimal
Total titratable acidity peaks at light-to-medium roast then declines; very dark roasts have low acidity but may taste harsh from quinic and acetic acids

References¶

Changelog¶

Date	Change
2026-04-27	Note created

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