A green bean smells of almost nothing and contains none of the aromas of roasted coffee. It contains their precursors, a stock of raw materials that heat will transform. Sucrose first, 7.3 to 11.4% of dry weight in arabica; it is not found in the cup, it is the fuel of the roasting reactions. Chlorogenic acids (CGAs) next, polyphenols of which 5-caffeoylquinic dominates: 13.6 mg per fruit in arabica, 16.9 mg in canephora, which offsets the gap by accumulating less sugar.

Yang et al. 2026, p. 3-5, 12; Moreira et al. 2012; Frank et al. 2007; RSC 2019

Lipids, 7 to 17% of dry weight, of which about a fifth is diterpenes (cafestol, kahweol); the difference in content between the two species exceeds 30%. Caffeine, finally, 0.9 to 1.5% in arabica according to the wide range in the literature (0.85 to 1.15% in the sample set of the 2026 review), about double in canephora, made by three methyltransferases (XMT, MXMT, DXMT) of which canephora has three highly expressed copies and arabica six less expressed ones.

Yang et al., Agriculture (2026), p. 3-5; LC ch. 16b and 17

Green coffee does not stop there. Added to it are trigonelline, an alkaloid that weighs about as much as caffeine, around 1% of dry weight. Then proteins and free amino acids. Then polysaccharides, arabinogalactans and galactomannans. Then organic acids already present in the fruit: citric, malic, phosphoric.

Each has a use later on, and that is how they are recognized. Amino acids supply the nitrogen without which the Maillard reaction cannot get started, since this reaction is by definition the meeting of a sugar and a nitrogen compound. Polysaccharides will make the framework of the melanoidins, those large brown molecules that color the cup. Trigonelline is mostly destined to be destroyed by heat.

This list reads as a ceiling, not an inventory. Everything that will come out in the cup is already present here, as raw material. The farm, the climate, the variety and the fermentation make up this stock; roasting only consumes it. A roaster therefore cannot add what the bean does not have.

The 2026 review draws the same boundary. It explicitly treats roasting as the step that consumes the precursors accumulated upstream, and stops there.

Yang et al. 2026, p. 12; Moreira et al., Food & Function 3 (2012), on melanoidins; Royal Society of Chemistry, Coffee: Production, Quality and Chemistry (2019), ch. Trigonelline and Derivatives; LC ch. 16b