Quick answer: Coffee roasting terms fall into five categories: bean biology (arabica, peaberry, varietals), preparation (green coffee, single-origin, blends), equipment (air roaster, drum roaster, roast profile), the roast sequence (charging, yellowing, first crack, Maillard reaction, second crack), and cup characteristics (acidity, body, finish). Knowing which category a term belongs to tells you exactly where in the process it matters.

If you have started reading about home roasting and hit a wall of jargon, you are not alone. The language around coffee roasting is genuinely technical. Roasters borrow from chemistry, agriculture, and sensory science all at once. This glossary cuts through it, organized by where each term shows up in the actual roasting process.

Bean biology: where coffee starts

You do not need to be a botanist, but a few biological terms show up constantly in sourcing conversations and on green-coffee spec sheets. Here is what they actually mean.

Bean Belt (also called the Coffee Belt): the band between the Tropics of Cancer and Capricorn where coffee grows commercially. Temperature, altitude, and rainfall in this zone produce the flavor variation that makes single-origin coffee worth talking about.

Coffee plant: a flowering shrub or tree in the genus Coffea, native to tropical Africa and Asia. Science has described more than 120 Coffea species, though only two dominate commercial production.

Arabica (Coffea arabica): the species behind roughly 70% of global coffee output. Brazil is the top producer. Arabica grows at higher altitudes, typically 1,800 to 6,300 feet, which contributes to its cleaner acidity and more complex flavor profile compared to Robusta.

Robusta (Coffea canephora): about 25% of global production, with Vietnam as the leading grower. Robusta has nearly double the caffeine content of Arabica and a heavier, earthier flavor. It is the backbone of most commercial espresso blends because of its crema production and lower cost.

Varietals and cultivars: both refer to specific variations within a species, the way Gala and Granny Smith are both apples. The technical distinction is that a varietal occurs naturally, while a cultivar is specifically bred. In practice, roasters use both terms loosely. For Arabica, Typica and Bourbon are the foundational varieties; most of the specialty-coffee catalog (Gesha, SL28, Caturra) traces back to one or both.

Coffee cherry: the fruit of the coffee plant, typically red or yellow when ripe, with two seeds (beans) inside. Processing determines how much of the cherry's flavor transfers to the final cup. Washed, natural, and honey processing each leave a different imprint.

Peaberry: a coffee fruit where only one seed develops instead of two, producing a round, dense bean rather than the flat-sided standard. Peaberries represent roughly 5% of any harvest. Whether they taste better is genuinely contested; they roast differently because of their round shape, which is the more defensible claim.

Green coffee and sourcing terms

Green coffee: unroasted coffee seeds after milling. Each bean is wrapped in a thin papery layer called silverskin, which gives the pile a greyish cast in bulk. Green coffee retains its origin character most distinctly before roasting begins. Those flavors become less obvious as heat progresses.

Single-origin coffee: green beans from one specific crop, farm, region, or country. Single-origin is a sourcing designation, not a quality guarantee, though it implies traceability. A washed Ethiopian Yirgacheffe and a natural Sumatran Mandheling are both single-origin; they taste nothing alike.

Coffee blend: a mix of two or more single-origin beans, combined either before roasting (pre-blending) or after (post-blending). Blends trade terroir specificity for consistency. Roasters can compensate for seasonal variation in one origin by adjusting the ratios of others.

Equipment: roaster types and roast profiles

Air roaster (fluid-bed roaster): hot air does double duty, heating the beans and keeping them agitated. Air roasters heat fast, produce clean cups, and suit home and small-scale commercial use. The Fresh Roast SR800 is the most widely used home air roaster; it handles 226 g batches and gives you independent heat and fan controls you can actually learn from.

Drum roaster: green beans tumble inside a rotating heated metal drum. Drum roasters are the standard for commercial roasting because they handle larger batch sizes and develop heavier body in the cup. The trade-off is more thermal mass to manage and more variables to track across a roast.

Roast profile: the record of temperatures, times, airflow, and any other tracked variables across a single roast. Think of it as a recipe log. Roasters use software like Cropster or Artisan to graph the profile in real time; home roasters often keep a handwritten journal. The profile is what makes a roast repeatable. Without it, you are guessing.

Rate of rise (RoR): the derivative of bean temperature over time, expressed in degrees per minute. RoR is the single most important number on a roast profile because it tells you where the roast is headed, not just where it is. A declining RoR in the development stage is expected and desirable. A stalling or negative RoR usually means you have run out of heat and will get a baked, flat cup.

The roast sequence, stage by stage

Coffee roasting follows a predictable thermal sequence. Each stage has a name, a temperature range, and a specific thing happening inside the bean. Here is what you are actually managing.

Charging: pre-heating the roaster before loading green beans. Charge temperature typically runs between 392°F and 428°F (200°C to 220°C) depending on batch size and machine. Getting the charge temperature right means your first batch behaves like your tenth. Without it, early batches run cold and develop unevenly.

Yellowing / drying stage: the first phase, where beans lose most of their moisture. Bean color shifts from green to yellow over the first several minutes. Internal bean temperature rises from ambient to roughly 300°F to 320°F (149°C to 160°C). The roaster is still doing evaporation work here; actual flavor development has not started yet.

Maillard reaction: a chain of chemical reactions between amino acids and simple sugars that begins around 280°F (138°C) and accelerates as temperatures rise. The Maillard reaction is responsible for browning the beans and generating most of coffee's flavor compounds. It is the same chemistry behind seared meat and toasted bread.

Caramelization: occurs at higher temperatures than the Maillard reaction, typically above 340°F (171°C). Sugars break down and recombine into hundreds of aromatic compounds, producing the sweetness and darker color of medium-to-dark roasts. You will smell it as caramel or toffee notes when you lean close to the roaster exhaust.

Strecker degradation: the conversion of amino acids into aldehydes, which are responsible for a large share of coffee's distinctive aroma compounds. The process also produces CO2 inside the beans, which later escapes during degassing.

First crack: at around 380°F to 400°F (193°C to 204°C), internal steam and CO2 pressure exceeds the bean's structural integrity and the bean physically fractures. You hear a series of audible pops, similar to popcorn but lower-pitched. First crack marks the beginning of drinkable coffee. Light roasts are dropped here or just after; medium roasts develop through the crack.

Development stage: the period between first and second crack, typically at 410°F to 430°F (210°C to 221°C). The roaster is managing development time ratio (DTR) here, which is the percentage of total roast time spent after first crack. DTR runs roughly 20 to 25% for most specialty roast profiles. Too short and the coffee is underdeveloped and grassy; too long and it goes flat.

Second crack: at around 435°F to 450°F (224°C to 232°C), CO2 pressure breaks through the bean surface a second time, more quietly than first crack. Bean oils are now visibly on the surface. Second crack marks the entry into dark-roast territory. Most specialty roasters drop their beans before or at the very beginning of second crack.

Roast problems: chaff, defects, and what causes them

Chaff: the silverskin that flakes off beans during roasting. Air roasters have a chaff collector that fills up. A clogged collector starves the roast of airflow and wrecks your RoR curve. Check it every 5 to 7 batches on natural-processed beans, which produce far more chaff than washed.

Chaff is also a fire hazard if it accumulates near a heat source. Do not skip that maintenance step.

Roast defects: the four main ones are under-development (grassy, sour, thin), over-development (flat, dull), scorching or tipping (bean surface burns while the interior stays underdeveloped, caused by too-high charge temperatures), and baking (long, slow roast with a declining RoR, producing a cardboard, lifeless cup). All four come from poor profile management, not from the beans.

After the roast: cooling and degassing

Cooling (quenching): rapidly dropping bean temperature after the drop to stop residual roasting. Most commercial roasters use forced-air cooling trays. Some industrial operations use a small water mist (true quenching), though this is controversial because it adds moisture back to the bean. For home roasters, getting beans to room temperature within 4 to 5 minutes is the target; slower than that and development keeps creeping.

Degassing: freshly roasted beans release CO2 for days to weeks after roasting. That CO2 needs to escape before you brew or you will get inconsistent extraction and off flavors. Most washed light-to-medium roasts peak between 5 and 14 days off roast. Natural-processed coffees off-gas more slowly and often benefit from a longer rest. One-way-valve bags let CO2 escape without letting oxygen in; do not use sealed airtight containers on beans less than 24 hours old or the bag will pressurize.

Cup characteristics: what you taste and why

Acidity: in coffee, acidity is a positive attribute, a brightness or crispness that lifts the cup. High-altitude Arabica (Ethiopian, Kenyan, Colombian) tends toward bright, fruit-forward acidity. It is not sourness; sourness is a defect. If you are getting unpleasant sharpness, check your water temperature and extraction time before blaming the bean.

Aroma: the smell of brewed coffee, distinct from fragrance (the smell of freshly ground beans) and bouquet (the smell of hot water hitting the grounds). Lighter roasts tend toward floral and fruit aromas; medium roasts shift toward chocolate and nuts; dark roasts toward smoke and caramel. The SCA Flavor Wheel maps roughly 110 aroma descriptors organized by category.

Body: the physical weight or texture of coffee in the mouth, what cupping forms call mouthfeel. Coffees grown at lower elevations and slow-roasted generally develop heavier body. Robusta-heavy blends feel thicker than straight Arabica. French press extraction produces more body than paper-filtered drip because the paper strips oils.

Flavor: the combined sensory impression of taste and aroma during and after drinking. Coffee's flavor compounds number in the thousands; roasting chemistry determines which ones end up dominant. A well-developed medium roast from a Bourbon varietal might show dried cherry, dark chocolate, and walnut. The same bean under-roasted tastes like hay.

Finish: the aftertaste that lingers after you swallow. A long, clean finish is the mark of a high-quality, well-roasted cup. Coffees with heavier body generally have a longer finish. Bitterness that lingers past 30 seconds suggests over-extraction or over-roasting, not a quality bean.

Roast types: light through dark

Roast names are not standardized across the industry, which causes real confusion. The Specialty Coffee Association uses Agtron color numbers (a spectrophotometric reading of the roasted bean surface) as the objective reference. The common names below map approximately to those ranges.

Light roast (Agtron ~70 to 85; also called Cinnamon, Half City, New England): bright acidity, delicate fruit and floral notes, light body. The bean's origin character is most distinct at this roast level. Requires precise temperature control and often benefits from a longer development time ratio than beginners expect.

Medium roast (Agtron ~55 to 65; also called American, Breakfast, City, City+): balanced acidity and body, chocolate and nut notes develop, sweetness increases. The widest roast band for specialty coffee; most Ethiopian and Central American single-origins are roasted in this range for retail.

Medium-dark roast (Agtron ~40 to 50; also called Full City, Vienna, After Dinner): acidity drops, body increases, roast flavors (caramel, dark chocolate, mild bitterness) become prominent. Full City is at the front edge of second crack; Vienna is pushing into it.

Dark roast (Agtron ~25 to 35; also called French, Italian, Neapolitan): heavy body, low acidity, dominant roast flavors. Bean oils are on the surface. Origin character is largely obscured by roast character at this level. Dark roasts need to be brewed within 2 to 3 weeks of roast date; the oils on the surface oxidize faster than unexpressed oils inside lighter-roasted beans.

Frequently Asked Questions

What is the difference between a varietal and a cultivar?

A varietal is a naturally occurring variation within a coffee species; a cultivar is specifically bred by humans. In practice, the coffee trade uses both terms interchangeably, and most spec sheets will not make the distinction. When you see "Gesha" or "SL28" on a bag, those are cultivars derived from Arabica.

What does "first crack" mean in coffee roasting?

First crack is the audible popping sound coffee beans make when internal steam and CO2 pressure exceeds the bean's structural limit, typically at 380°F to 400°F (193°C to 204°C). It marks the minimum threshold for drinkable coffee. Light roasts are dropped at or just after first crack; medium and dark roasts develop past it.

What is a roast profile and why does it matter?

A roast profile is the logged record of temperatures, times, and other variables across a roast. It is what makes a roast reproducible. Without a profile, you are tasting a result you cannot reliably repeat. Home roasters can track profiles in a notebook; software tools like Artisan or Cropster graph them in real time and connect to probe sensors on the roaster.

How long should coffee degas before brewing?

Most washed light-to-medium roasts need 5 to 14 days off roast before they are at peak flavor. Natural-processed coffees typically need longer, sometimes up to 21 days. Brewing beans within 24 to 48 hours of roasting produces inconsistent extraction because CO2 is still actively escaping and interferes with water contact. Espresso extraction is most sensitive to degassing time; filter brewing is more forgiving.

What is the difference between an air roaster and a drum roaster?

Air roasters (fluid-bed) use hot air to simultaneously heat and agitate the beans; drum roasters tumble beans in a rotating heated drum. Air roasters heat faster, are easier to learn on, and produce cleaner, brighter cups. Drum roasters develop heavier body and handle larger batches. CoffeeRoast Co. carries both types; if you are starting out, an air roaster like the Fresh Roast SR800 gives you the most feedback per dollar.

What causes roast defects?

The four main roast defects are under-development (grassy, thin), over-development (flat, dull), scorching or tipping (surface burns while interior stays raw, caused by a too-high charge temperature), and baking (low, slow heat with a stalling RoR, producing a cardboard-like cup). All are profile management problems. The beans are not at fault.

What is rate of rise (RoR) and should I track it?

Rate of rise is the speed at which bean temperature is increasing, measured in degrees per minute. It is the most predictive number on a roast profile because it tells you where the roast is going before it gets there. A healthy RoR curve rises through the drying stage, peaks around yellowing, then declines steadily through development. A flatlining or crashing RoR in development signals a baked roast in progress.

Key takeaways:

• Coffee roasting terms cluster into five areas: biology, sourcing, equipment, roast stages, and cup characteristics. Learning which cluster a term belongs to tells you when and why it matters.
• First crack (380°F to 400°F) is the single most important event in a roast. Light roasts drop here; medium and dark roasts develop past it using development time ratio as the guide.
• Rate of rise (RoR) is more useful than bean temperature alone because it shows direction, not just position. A stalling RoR during development produces baked coffee regardless of the final temperature reached.
• Degassing is not optional. Most washed roasts need 5 to 14 days off roast before brewing; natural-processed coffees need longer. One-way-valve storage preserves freshness without pressurizing.
• Roast defects are caused by profile management errors, not bad beans. Under-development, over-development, scorching, and baking each have a specific cause and a specific fix.

Ready to put these terms to use? CoffeeRoast Co.'s guides on how to roast coffee at home, selecting beans for roasting, and comparing an air roaster to a drum roaster are the natural next steps.