tags: [] - coffee/science - coffee/education aliases: - Coffee chemistry introduction - Basic coffee chemistry - Coffee compounds overview

Coffee Chemistry Basics¶

Tags: #coffee/science #coffee/education Aliases: Coffee chemistry introduction, Basic coffee chemistry, Coffee compounds overview Related: Coffee Chemistry | Roasting | Extraction Yield | Sensory Science | Brewing Fundamentals MOC Status: ✅ Complete

Overview¶

Coffee chemistry basics covers the foundational chemical concepts needed to understand why coffee tastes the way it does — from the composition of the green bean through the transformations of roasting and the selective extraction of brewing. Coffee is one of the most chemically complex beverages consumed regularly, containing over 1,000 identified compounds in roasted form, of which a subset are responsible for its distinctive flavour, aroma, body, and stimulant effects. A basic understanding of the key compound classes — caffeine, chlorogenic acids, sugars, lipids, and volatile aromatics — enables brewers, roasters, and enthusiasts to make informed decisions about every variable in the coffee process.

[!NOTE] This is an introductory overview. For comprehensive compound-level detail, see Coffee Chemistry.

The Bean Before Roasting¶

Green coffee is a seed — chemically, it is predominantly: - Carbohydrates (50–60% dry weight): Sucrose (~8%), polysaccharides (cellulose, mannans) forming the structural cell walls - Lipids (12–18%): Oils, waxes, and diterpenes (cafestol and kahweol) stored inside the bean cells - Proteins and amino acids (10–13%): Building blocks for the Maillard reaction during roasting - Chlorogenic acids (6–10% in Arabica): Polyphenols; antioxidants; bitterness precursors - Caffeine (1.2–1.5% in Arabica): The primary stimulant alkaloid - Water (~10%): Moisture content; drives initial roasting phase

None of the flavours associated with roasted coffee are present in the green bean — all characteristic coffee flavour is created during roasting.

What Roasting Does to the Bean¶

Roasting transforms the green bean through two primary chemical processes:

The Maillard Reaction¶

The Maillard reaction occurs between amino acids (from proteins) and reducing sugars when heated above approximately 150°C. It produces: - Hundreds of new flavour compounds — pyrazines (nutty, roasty), furans (caramel, sweet), thiols (potent "coffee" aroma), aldehydes - Brown colour (melanoidins) — the characteristic dark colour of roasted coffee - Complexity — the Maillard reaction is responsible for most of the characteristic roasted flavour of coffee

Caramelisation¶

Sucrose (the dominant sugar in green coffee) undergoes caramelisation above ~170°C, producing: - Caramel, butterscotch, toffee compounds - Further darkening of colour - Sweet aromatic compounds

By the end of roasting, all sucrose is destroyed — none remains in the roasted bean.

Chlorogenic Acid Degradation¶

Chlorogenic acids degrade during roasting into: - Quinic acid: Harsh, bitter; increases with roast degree - Chlorogenic acid lactones: Bitter compounds; responsible for a significant portion of coffee's bitterness - Darker roasts degrade more CGAs, producing more bitter compounds

What Extraction Selects From the Roasted Bean¶

When hot water contacts ground coffee, it selectively extracts compounds in sequence by solubility and molecular weight:

Extraction phase	Compounds extracted	Cup character
Early (fast)	CO₂, volatile aromatics, simple acids, bright esters	Sour, bright, fruity
Middle	Sugars (Maillard products), complex organic acids	Sweet, balanced, body
Late (slow)	Phenolic bitter compounds, heavy tannins, harsh lactones	Bitter, astringent, harsh

The brewer controls extraction by adjusting grind size, temperature, time, and ratio — the goal is to maximise extraction of the desirable middle-phase compounds while limiting the harsh late-phase compounds.

The Four Taste Components in Coffee¶

Acidity: Organic acids — citric (citrus), malic (apple), phosphoric (mineral), acetic (vinegar at high concentrations)
Bitterness: Caffeine (~10–15% of perceived bitterness), chlorogenic acid degradation products (lactones, quinic acid — the majority of bitterness), Maillard reaction products
Sweetness: Remaining Maillard caramelisation products; no sucrose survives roasting; perceived sweetness from ester and aldehyde compounds
Body: Dissolved solids (total extract), lipids (oils), suspended fine particles — physical rather than taste-receptor sensation

Key Facts¶

Green coffee contains carbohydrates, lipids, proteins, chlorogenic acids, caffeine, and water — none of the characteristic roast flavour is present before roasting
Maillard reaction (amino acids + sugars under heat) creates hundreds of aroma compounds; caramelisation creates sweet compounds; both give roasted coffee its flavour
All sucrose is destroyed during roasting — perceived sweetness in coffee comes from Maillard products and certain organic acids
Chlorogenic acids degrade into bitter quinic acid and lactones — more bitter in darker roasts
Extraction sequence: bright acids first, sweetness and body in the middle, bitterness and astringency last — the brewer's task is to stop at the right point
Caffeine contributes only ~10–15% of perceived bitterness; the majority comes from CGA degradation products

References¶

Changelog¶

Date	Change
2026-04-28	Note created

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