The smell of green coffee beans bears little similarity to the smell of roasted coffee. Only a handful of aroma compounds found in green coffee survive the roasting process; instead, nearly all of coffee’s distinctive flavours are created during roasting. The chemical reactions, which involve a fairly simple set of compounds in the green beans, can result in a complex mixture of aroma and flavour compounds.
Very small differences in the composition of green beans can account for the distinct flavours of coffees. Almost all the components of a green coffee bean contribute to a coffee’s flavour and colour — even the water content affects the final quality of the coffee (Poisson et al 2017). The most important flavour precursors are sugars, proteins, free amino acids, trigonelline, and chlorogenic acids.
The composition of green coffee varies, depending on the variety, origin, processing method, and climate. The table below describes the main components of green coffee.
| Chemical Composition of Green Coffee, as a Percentage of Dry Weight | |||
| Constituents | Arabica | Robusta | Components |
| Soluble carbohydrates | 9–12.5% | 6–11.5% | |
| Monosaccharides | 0.2–0.5% | Fructose, glucose, galactose, and traces of arabinose | |
| Oligosaccharides | 6–9% | 3–7% | Sucrose (>90%), raffinose (0–0.9%), and stachyose (0–0.13%) |
| Polysaccharides | 3–4% | Polymers of galactose (55–65%), mannose (10–20%), arabinose (20–35%), and glucose (0–2%) | |
| Insoluble carbohydrates | 46–53% | 34–44% | |
| Hemicelluloses | 5–10% | 3–4% | Polymers of galactose (65–75%), arabinose (25–30%), and mannose (0–10%) |
| Cellulose, β(1–4)mannan | 41–43% | 32–40% | |
| Acids and phenols | |||
| Volatile acids | 0.1% | ||
| Nonvolatile acids | 1.7–2.9% | 1.3–2.2% | Citric acid, |