Kaiserblick Knowledge

Roasting

12 min read

Roasting

Sources: El Arte del Café by Sébastien Racineux & Chung-Leng Tran (Lunwerg, 2017); The Coffee Brewing Handbook by Rob Lingle (SCA, 2011); Coffee Sensory and Cupping Handbook by Fernández-Alduenda & Giuliano (SCA, 2021); Espresso Extraction: Measurement and Mastery by Scott Rao (2013); The Coffee Roaster’s Companion by Scott Rao (2014)

Roasting is a thermal process that transforms the chemical composition of green coffee, developing aromas and flavours that do not exist in the raw bean. The roaster’s role is to reveal the potential of each green coffee — inherited from its terroir, variety, and processing — without masking it. (source: El Arte del Café)

Roast Degrees

No universal nomenclature exists — what one roaster calls “light” another may call “full city.” The following definitions represent common specialty-industry usage (source: The Coffee Roaster’s Companion by Scott Rao (2014)):

DegreeTimingCup character
CinnamonEarly first crackAcidic, grassy, peanutty; very light body
CityEnd of / just after first crackAcidic, winey, sweet, floral, fruity; light body
Full CityJust before second crackCaramelly, ripe fruit, medium body
VienneseEarly second crack, first surface oilsBittersweet, caramelly, nutty, heavy body
FrenchAfter surface oils appearBurnt, bitter, smoky, heavy body
ItalianDarkest commercial roastBurnt, acrid, rancid, carbonized

Acidity peaks at city roast; aromatics peak at city–full city; body peaks near French roast; extraction potential is highest at French and declines as pyrolysis burns off soluble mass.

The Two Cracks

As temperature rises, two distinct exothermic events occur in the bean:

First crack (~200°C): Water vapour and CO₂ expand, causing the bean to crack audibly. This marks the beginning of drinkable coffee. Most specialty roasters stop somewhere after first crack.

Second crack (~225°C): Cell structure begins to break down. Oils migrate to the surface. Characteristic shiny, dark appearance. Beyond this point, roast flavours dominate over origin character.

Temperature and the Bean

The bean temperature follows a characteristic curve:

  • Initial drop as the cold beans absorb heat from the drum
  • Steady climb through drying phase
  • Acceleration through Maillard reactions
  • First crack, then continued development
  • Roaster decides when to stop (drop point)

Caffeine stability: Caffeine content remains almost stable regardless of roast level — approximately 10% loss at most. The perception of stronger coffee with dark roast is a taste illusion related to bitterness, not actual caffeine increase. (source: El Arte del Café)

Roasting Chemistry

Maillard reactions: Nonenzymatic browning between amino acids and reducing sugars. Begin at ~250–300°F (121–149°C); self-sustaining at 320°F (160°C). Produce bittersweet flavor, brown color, and roasted/meaty aromas. (source: The Coffee Roaster’s Companion by Scott Rao (2014))

Caramelization: Pyrolysis (thermal decomposition) of sugars beginning at ~340°F (171°C). Produces fruity, caramelly, nutty aromas. Counterintuitively, caramelization decreases sweetness and increases bitterness — lighter roasts are sweeter, not darker ones. (source: The Coffee Roaster’s Companion by Scott Rao (2014))

Caffeine: Stable at roasting temperatures. Caffeine content by weight increases in darker roasts because the bean loses mass (water and organic matter) while caffeine is preserved. Darker roasts yield higher caffeine per gram, not lower. This directly contradicts the popular belief. (source: The Coffee Roaster’s Companion by Scott Rao (2014))

Note: El Arte del Café states “approximately 10% caffeine loss at most” from roasting — Rao disputes this, citing research showing caffeine is essentially unchanged. (source: El Arte del Café by Racineux & Tran (2017))

Aroma: 800+ volatile aromatic compounds develop during roasting. Aroma peaks at light–medium roast. With further roasting, aroma destruction outpaces creation and aromatics become smokier. Oils in the bean dissolve and slowly release volatile aromatics — darker, more porous roasts lose aromatics faster.

The Three Commandments (Rao)

Derived from analysis of 20,000+ batches, Rao’s three rules apply to all beans and machines for light-to-medium roasting:

  1. Apply adequate energy at the start — a large temperature gradient (ΔT) early drives inner-bean development; insufficient early energy cannot be compensated later
  2. Rate of Rise (ROR) must always decelerate — any flatline or increase creates flat, papery, or baked flavors; a full stall eliminates sweetness entirely
  3. First crack at 75–80% of total roast time — Development Time Ratio (DTR) of 20–25% ensures adequate development without baking

See Roast Development for the full treatment and practical application. (source: The Coffee Roaster’s Companion by Scott Rao (2014))

Roast Profile vs. Roast Level

This is the most important distinction in modern specialty roasting.

Roast level = the endpoint (colour, temperature at drop). Two beans of the same roast colour are not the same coffee.

Roast profile = the path taken to reach that endpoint — the rate of temperature rise, timing of first crack relative to total roast time, duration of development phase.

Two identical green coffees roasted to the same start and end point, but with different profiles, will produce completely different cups. The roaster “interprets” the coffee and imprints their style. (source: El Arte del Café)

Development time ratio (DTR): The time between first crack and drop, expressed as a percentage of total roast time. A key quality variable — too short = underdeveloped (grassy, astringent); too long = flat, baked.

Light Roast and Acidity

Beyond a certain point, roast flavours (caramel, then smoke, bitter, burnt) mask the origin character of the coffee. Only a light roast allows the coffee’s own aromatics to be preserved. (source: El Arte del Café)

Flavour development during roasting:

  • Acidity: Citric and malic acids reach maximum concentration at light roast, then decline progressively. Chlorogenic acids (beneficial polyphenols) break down into quinic and caffeic acids (astringent) as roast darkens.
  • Aromas: Develop in the early-to-mid phases; light roast captures more of the aromatic spectrum.
  • Body: Generally increases with roast level.
  • Sweetness: Peaks in medium roast (Maillard caramelisation); diminishes in dark roast as sugars carbonise.

A light, fast roast produces beans with maximum acidity potential.

Colour as an unreliable indicator: There is no universal colour code for roast level. A better method is to track the time of first crack relative to total process duration. (source: El Arte del Café)

Roast Style by Preparation Method

The same coffee can be roasted differently depending on the intended brewing method:

  • Filter / soft methods: prefer lighter roast — acidity and aromatic subtlety are amplified by long, gentle extraction (3+ minutes)
  • Espresso: a slightly darker roast balances the intense 20-30 second extraction, which tends to amplify acidity from a light roast

Some roasters produce a single roast; others offer method-specific roasts for the same green lot. (source: El Arte del Café)

Regional consumer preferences: Scandinavian markets favour light roast for filter; Mediterranean markets favour dark roast for espresso. Within a single country, preferences can vary significantly (e.g., northern vs. southern Italy).

Single Origin vs. Blend

Single origin (origen puro): Beans from one farm or one washing station harvest. Offers a unique, distinctive character — the terroir, variety, processing, and producer’s work readable through the cup. Ideal for filter/soft methods where subtlety is amplified.

The strictest definition of single origin requires single farm + single variety. In practice, blending varieties from different altitudes on the same farm is common and agronomically rational (disease risk diversification, complementary flavour complexity). (source: El Arte del Café)

Blend (mezcla): Combines coffees from different origins to achieve a consistent, accessible flavour. Better suited to espresso: the method is demanding and inconsistent; a well-constructed blend compensates for this and combines the qualities of its components.

Central American coffees in blend context: Coffees from Costa Rica, El Salvador, and Guatemala offer “aromatic complexity and acidity” — the best lots work well as single origins for filter. (source: El Arte del Café)

Building a blend

  1. Define the target (espresso/filter, aromatic nuances desired)
  2. Select origins (limit to 3–4 maximum; beyond this, individual qualities dilute each other)
  3. Calibrate proportions (start equal, then adjust: halve the proportion of any dominant origin; double any origin that’s too discrete)

Example blend: 50% Brazil / 25% Guatemala / 25% Ethiopia.

How to Read a Coffee Package

Key information to look for:

Label elementWhat it tells you
Roast dateCoffee is a fresh product; allow 5 days before brewing (filter), 1 week+ (espresso); best 2-3 weeks post-roast for espresso
Harvest year / originTraceability; basis for detecting past crop
Region, farm, producerLevel of traceability
AltitudeIndicator of potential cup quality
VarietyCup character expectations
Drying methodNatural vs. washed flavour profile
Recommended preparationEspresso vs. filter icon
ValveOne-way degassing valve = better preservation

Marketing traps to avoid: “Coffee strength” on mass-market bags refers to roast intensity or grind fineness, not caffeine. “100% Arabica” is baseline, not a quality claim. “Slow roast” is not inherently better — a well-executed 12-minute roast can outperform a 18-minute one. (source: El Arte del Café)

Coffee Storage (Post-Roast)

Enemies of roasted coffee: high temperatures, oxygen, humidity, extreme dryness, light.

Storage locationVerdict
Dark cupboard, hermetic bagIdeal
Freezer (sealed bag, unopened)Good for long-term beyond best-before date; but accelerates ageing once removed
RefrigeratorNot recommended — coffee is porous and absorbs food odours; condensation risk

Ground coffee deteriorates much faster than whole bean (greater surface area; CO₂ — a natural preservative — dissipates immediately on grinding).

Package types:

  • Kraft/multilayer sealed (no valve): cheapest; poor preservation; no best-before indicated
  • Hermetic with valve + zipper: used by most artisan roasters; 3 months sealed, days once opened
  • Nitrogen-flushed (cans or bags): best preservation, up to 1 year; expensive infrastructure
  • Vacuum-sealed: correct preservation; some volatile aromatics lost during the process; up to 3 months

Roast Level and Brewing Chemistry

The degree of roast has direct consequences for how the coffee extracts and tastes in the cup — relevant for brewing guidance given to customers.

Trigonelline is a bitter organic compound present in green coffee at ~1% by weight (same as caffeine in Arabica). Its behaviour during roasting tracks directly with roast level:

  • Light roast (bean temp below ~218°C): ~10% degradation — most trigonelline preserved
  • Medium to moderately dark roast (~235°C): ~80% degradation
  • Very dark roast (above ~246°C): ~100% degradation

Trigonelline extracts into the brew very rapidly (>80% in the first 2 minutes). Its preservation in light roasts is a measurable quality marker. (source: SCA Coffee Brewing Handbook)

Chlorogenic acids break down progressively during roasting. The breakdown products are chemically distinct and have different sensory roles:

  • Chlorogenic acid lactones (formed at light-medium roast): primarily bitter compounds — account for up to 30% of coffee bitterness
  • Phenylindanes (formed at higher temperatures from lactone breakdown): also bitter, account for up to 30% of bitterness; harsh, lingering bitterness in dark roasts; emerging research suggests neuroprotective properties (amyloid-beta inhibition) — not yet established clinical fact
  • Quinic acid and caffeic acid: sour and astringent contributors

Light roast preserves the most intact chlorogenic acid — beneficial for antioxidant properties and cleaner flavour. However, chlorogenic acid continues to break down after brewing during holding, creating sour/bitter off-flavours. See Coffee Freshness. (source: SCA Coffee Brewing Handbook; SCA Coffee Sensory and Cupping Handbook)

Phenolic compounds are present at low concentrations in light roasts. They increase as roasting continues. Phenols contribute smoky, spicy, astringent characteristics — another reason light roasts produce cleaner, less astringent cups.

Arabica vs. Robusta: Arabica coffees have lower chlorogenic acid and phenol content than Robusta — explaining their objectively superior cup quality in filter brewing. This is a measurable scientific basis for Kaiserblick’s Arabica-only position. (source: SCA Coffee Brewing Handbook)

Light roast grinding: Light roasted beans are tenacious, pliable, and tough — they do not break apart as easily as dark roasted beans, always produce fewer fine particles at the same grinder setting. Customers must set their grinders finer when using light roast coffee. See Grind. (source: SCA Coffee Brewing Handbook)

Roast Development and Espresso Extraction

This section is specific to espresso end-use of Kaiserblick’s roasted coffee.

The internal structure of a coffee bean is a three-dimensional cellulose web coated with soluble flavouring compounds. Roasting makes cellulose more porous, allowing water to penetrate during brewing. Underdeveloped sections remain non-porous — water cannot enter, and the soluble material locked inside cannot be extracted.

The practical consequence for espresso: underdeveloped roasts extract 1–4 percentage points lower than properly developed batches of the same coffee. A barista targeting 19–20% may land at 15–17% without being able to diagnose why, since no grind adjustment will fully compensate for closed cellulose. (source: Espresso Extraction: Measurement and Mastery by Scott Rao (2013))

Diagnostic protocol — evaluating roast development without a refractometer:

  1. Prepare coffee for cupping (boil water, grind as for cupping)
  2. Allow water to cool to 95°C before pouring
  3. Pour over grounds; immediately bring nose to the surface
  4. Break the crust with a cupping spoon; smell the aroma carefully
  5. Break and agitate several times
Aroma detectedInterpretation
Broccoli, turnips, celerySevere underdevelopment
Grass, strawModerate underdevelopment
Clean, sweet, fruityGood development

Note: some origins (e.g., Sumatran coffees) may show herbaceous notes that are intrinsic rather than defective. (source: Espresso Extraction: Measurement and Mastery by Scott Rao (2013))

Tension with light roasting: Rao explicitly flags the trend toward very light roasting as a frequent cause of underdevelopment. Roasters seeking to work at the lightest possible color must be especially rigorous about development time ratio (DTR) to ensure porosity without adding roast character. See Development time ratio (DTR) above.

Relevance to Kaiserblick

Roxanne Fredericksen leads roast profile development at Kaiserblick. The company’s stated approach is light roast profiles for every micro-lot, designed to reveal specific flavours for filter extraction — directly aligned with the principles in this source. See Roasting Service.

For espresso lots specifically: full roast development is non-negotiable for reaching 19–20% extraction targets. The DTR and the cupping aroma test above are the primary quality checks. Use a Coffee Refractometer to verify extraction during espresso profile development.

Graph View

Backlinks