Roasting Science

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RS 2.07 Recap and Glossary


  • The most important flavour precursors are sugars, proteins, free amino acids, trigonelline, and chlorogenic acids.
  • Compared with robusta, arabica coffee contains larger amounts of carbohydrates and lipids and smaller amounts of chlorogenic acids and caffeine.
  • Soluble carbohydrates, especially sucrose and polysaccharides containing arabinose, are important flavour precursors in coffee.
  • Chlorogenic acids break down during roasting to form phenolic compounds that can impart coffee spice, floral, or vanilla aromas. In high concentrations, for example in dark-roasted coffee, these compounds are bitter and astringent and have woody, smoky, leathery, or medicinal flavours.
  • Lipids are heat stable and mostly survive roasting intact.
  • Free amino acids have the most important effect on coffee’s flavour. The different amino acids available contribute to the complexity of aromas formed in the Maillard reactions.
  • The amount of caffeine barely changes during roasting.
  • The moisture content is one of the biggest factors that determines how much energy is needed to roast coffee. Moisture content is also linked to bean density.
  • High-density beans conduct heat more effectively than low-density ones but require more energy to achieve the same increase in temperature. For this reason, most roasters choose to use a higher charge temperature when roasting denser beans.
  • Bean hardness is often conflated with density, but hardness and density may not be closely related. The effect of hardness on roasting is unknown.
  • Larger beans need more heat or more roasting time to become fully developed. Bean size may be less important in hot-air roasters, however, thanks to their efficient heat transfer.
  • Proper storage can prevent coffee from developing rancid off flavours — but no packaging or storage method entirely prevents coffee flavour from fading. Vacuum packs and other types of high-barrier packaging offer similar performance in maintaining quality over time.
  • Low-moisture coffees retain their quality for longer, probably because of reduced microbial activity.



Arabinose A monosaccharide that contains five carbon atoms (unlike glucose,