Roast
What heat does to the seed, and how roasters control it.
Basics
2 entries · 1 coming- OverviewRoastingDry heat that turns dense, green coffee seeds into brittle, porous, brown beans – forming aroma, taste and colour, driving off water and building up carbon dioxide.Source-checked
- OverviewGreen coffee compositionWhat green coffee is made of – carbohydrates, proteins and amino acids, lipids, acids, alkaloids, minerals and water – how arabica and robusta differ, and which constituents the roast turns into flavour and colour.Source-checked
- Overview · comingHistory of roasting
Steps, in order
From charge to cooling- 1Preheating and chargeThe first step of a roast – heating the empty roaster to a steady state, then charging the green coffee. What charge temperature means, why the probe reading drops to a turning point, and what studies show.Source-checked
- 2Drying phaseThe first stage of a roast, from charge to the visible yellowing of the beans – water heats up and evaporates, the bean starts to swell, and much of the heat goes into warming and evaporating that water.Source-checked
- 3Browning phaseThe stretch of a roast between yellowing and first crack, often called the Maillard phase – when the bean darkens fastest, loses most of its sucrose, forms new acids and aroma, and builds up the gas that ends in first crack.Source-checked
- 4First crackThe first audible cracking of the beans during a roast – what breaks inside the bean, how it sounds, which temperatures are reported, whether heat is released, and why roasters time development and roast degree from it.Source-checked
- 5Development timeThe time from first crack to the end of the roast – how it is measured, what the development time ratio is, and what studies found when only this phase was changed at the same roast colour.Source-checked
- 6Second crackThe second, snapping series of cracks heard when a roast is taken dark – what breaks in the bean, why oil reaches the surface, how flavour and chemistry change, and the smoke and gas that come with it.Source-checked
- 7Cooling and quenchingThe last step of the roast – how air coolers and water quenching stop the roast at the intended degree, why quench water stays in the bean, and what it changes for grinding, freshness and the legal moisture limit.Source-checked
Profiling and control
5 entries- ProfilingRoast profilesThe time–temperature curve of a roast – what the probes really measure, how rate of rise, turning point, first crack and development time are read, how roasters steer the curve, and what research says about profiles and flavour.Source-checked
- ProfilingRate of riseHow fast the bean-probe temperature climbs during a roast – how software calculates it, why it usually falls, why it describes the probe as much as the beans, and what studies have measured.Source-checked
- ProfilingTurning pointThe lowest bean-probe reading after the charge, where the curve stops falling and starts to climb. Why it is a feature of the probe rather than the beans, what moves it, and what it can and cannot tell a roaster.Source-checked
- ProfilingAirflowThe stream of air drawn through a coffee roaster – how it carries heat to the beans, takes water vapour and chaff away, how much air different roaster designs use, and what changing it does to the roast.Source-checked
- ProfilingHeat transferHow heat moves from the burner to the bean and into it – conduction, convection and radiation in a roaster, how roaster designs shift the balance, and why the slow flow of heat inside the bean matters for even roasting.Source-checked
Roast science
5 entries- ScienceGlass–rubber transitionHow the material of the coffee bean switches between a rigid, glassy state and a soft, rubbery one, how water and heat drive the change, and what it means for swelling in the roaster, grinding and storage.Source-checked
- SciencePorosity and cell structureHow roasting turns the dense, thick-walled cells of green coffee into a swollen, porous structure – and why those pores decide how a bean holds gas, sweats oil, grinds and extracts.Source-checked
- ScienceWater in roastingWhere the water in a roast comes from and where it goes – the green coffee's own moisture, water formed by reactions, the heat needed to evaporate it, the steam that swells the bean, and the little that is left at the end.Source-checked
- ScienceEndothermic and exothermic phasesWhy a roast first soaks up heat and later starts to release heat of its own – what calorimetry and models show, why nobody agrees where the switch happens, and what it means for heat control and cooling.Source-checked
- ScienceBean size and densityHow large and how dense green coffee beans are, how both are measured, and what they mean for roasting – heat uptake, evenness, and the swelling that lowers density as the roast goes on.Source-checked
Roast chemistry
11 entries- ChemistryMaillard reactionThe chain of reactions between sugars and amino acids that browns roasting coffee and forms much of its aroma – running through the whole roast, at rates that change with temperature, time and roast degree.Source-checked
- ChemistryStrecker degradationA branch of the Maillard network in which amino acids react with sugar-derived dicarbonyls during roasting, giving malty, potato-like and honey-like aldehydes, carbon dioxide and building blocks for pyrazines.Source-checked
- ChemistryCaramelisationThe breakdown of sugars by heat alone, without amino acids. In roasting coffee it runs alongside the Maillard reaction, shares many of its products, and leaves almost no sugar behind.Source-checked
- ChemistryChlorogenic acidsThe family of phenolic acids that makes up a large share of green coffee – how roasting breaks them down into bitter lactones, phenols and melanoidin material, and why their loss tracks roast degree.Source-checked
- ChemistryMelanoidinsThe brown, high-molecular-weight compounds that form late in roasting and give roasted coffee its colour – built on polysaccharides and protein, with chlorogenic acids worked in, and still without a known structure.Source-checked
- ChemistryAcids in coffeeThe acids behind coffee's sourness – which ones the green bean brings, which form or break down during roasting, how acidity is measured, and why the cup's acidity is not the taste of any single acid.Source-checked
- ChemistryCaffeine and roast degreeWhether light or dark roasts hold more caffeine – what roasting does to caffeine in the bean, why the answer depends on counting per bean, per gram or per scoop, and what reaches the cup.Source-checked
- ChemistryCarbohydrates and bodyHalf of green coffee is carbohydrate, mostly cell-wall polysaccharides. Roasting burns off the sugar and breaks part of the polysaccharides down; what dissolves helps shape viscosity, crema and, by most accounts, body.Source-checked
- ChemistryCoffee oilThe fat of the coffee bean – what it is made of, where it sits in the cell, why it reaches the surface of dark and ageing beans, how much of it ends up in each brew, and how its oxidation makes coffee stale.Source-checked
- ChemistryRoast gases and CO₂The gases a coffee bean forms while it roasts – mostly carbon dioxide, plus water vapour, carbon monoxide and aroma compounds – which reactions make them, how much leaves in the roaster and how much stays trapped.Source-checked
- ChemistryRoasting contaminantsUnwanted compounds that form in coffee during roasting – acrylamide, furan and methylfurans, and traces of polycyclic aromatic hydrocarbons – how roast degree shifts them and what food authorities say and require.Source-checked
Results and quality control
3 entries · 3 coming- QualityRoast degree and colourHow far a coffee has been roasted, and how it is measured – mostly as colour, by reflected light on ground coffee – with the scales in use, why they do not convert, and what colour does and does not tell.Source-checked
- QualityRoast lossThe weight green coffee loses in the roaster, as a share of its starting weight – mostly water, plus carbon dioxide, other volatiles and chaff. A roast-degree index next to colour, and the step from green to roasted cost.Source-checked
- Quality · comingVolume and bulk density
- QualityRoast defectsFlaws the roast itself puts into coffee – underdeveloped, baked, over-roasted, scorched, tipped, faced, cratered or uneven beans – how each looks, what causes it in the roaster, how it affects flavour and how to catch it.Source-checked
- Quality · comingRoast quality control
- Quality · comingBlending before or after roasting
Roasters
4 entries · 2 coming- RoasterDrum roastersThe most widespread batch coffee roaster – a heated, rotating drum through which hot air is drawn. How it is built, how heat reaches the beans, what the burner, airflow and drum speed controls do, and how batch size changes bean motion.Source-checked
- RoasterFluid-bed roastersHot-air roasters with no moving parts in the roasting chamber – a stream of hot air lifts, mixes and heats the beans, mainly by convection. Common in research, in sample roasting and in some industrial designs.Source-checked
- RoasterTangential and centrifugal roastersTwo industrial batch roaster designs that move the beans without turning a drum – rotating paddles in a fixed chamber, or a spinning bowl with fixed guides – and how their air paths differ from a drum's.Source-checked
- Roaster · comingSample roasters
- Roaster · comingRoaster energy use
- RoasterRoaster emissionsWhat leaves a coffee roastery through its stacks – smoke, volatile organic compounds, carbon monoxide, dust and chaff – where it comes from, why it rises late in the roast, how it is cleaned and how authorities regulate it.Source-checked
After the roast
3 entries- After the roastFreshness and storageWhat happens to roasted coffee, whole and ground, between the roaster and the cup – gas loss, aroma loss and oxidation – what speeds it up, and how roasteries, cafés and homes slow it down.Source-checked
- After the roastDegassingThe gas that roasting traps inside coffee – mostly carbon dioxide, with some carbon monoxide – where it is held, how it escapes by flow and diffusion, what speeds it up, how it is measured, and what it means for packing, brewing and safety.Source-checked
- After the roastCoffee packagingWhat packaging for roasted coffee has to do, how its materials trade barrier against recyclability, how packaging compares with wasted coffee in life-cycle studies, and the packaging and capsule rules in the EU and beyond.Source-checked
Special coffees
1 entry · 1 comingHistory
2 coming- History · comingIndustrial roasting history
- History · comingCoffee substitutes