Kaiserblick Knowledge

Grind

8 min read

Grind

Sources: The Coffee Brewing Handbook by Rob Lingle (SCA, 2011); Espresso Extraction: Measurement and Mastery by Scott Rao (2013); The Physics of Filter Coffee by Jonathan Gagné (2020)

Grinding increases the surface area of roasted coffee exposed to water, enabling extraction of soluble flavouring compounds. A whole bean placed in hot water would eventually yield an extract, but the time required would be impractical. Grinding a single bean to fine grind creates more than 4,000 times the number of particles and 16 times the surface area per unit weight. (source: SCA Coffee Brewing Handbook)

Why Grind Matters

The smaller the particle, the shorter the distance from any point inside the particle to its surface. This reduces both the time and distance that dissolved flavouring material must travel to reach the surrounding water — extraction is faster and more complete.

However, grinding also exposes more CO₂ (from roasting), oils, and ultra-fine particles that form brew colloids and contribute to body.

The fundamental rule: Grind must be matched to brewing time. A grind too coarse for the brewing time → under-extraction (grassy, under-developed). A grind too fine for the brewing time → over-extraction (bitter, astringent). (source: SCA Coffee Brewing Handbook)

Grind ClassBrewing TimeTypical Use
Fine1–4 minutesSingle-cup brewers, some filter
Drip4–6 minutesFilter-drip machines
Regular6–8 minutesCoffee urns, percolators
Espresso20–30 secondsPressurized infusion only

Particle Size Distribution and D₁₀

No grinding process produces perfectly uniform particles. The goal is a uniform distribution within a specified range. The U.S. Department of Commerce established standard grind designations in 1948, measured by Tyler mesh sieve analysis:

GrindRetained on #10 & #14 meshPassing through #28 mesh
Regular55%12%
Drip7%20%
Fine0%30%

The most important variable in each designation is the percentage passing through the #28 mesh sieve — this represents the very fine particles that most directly affect extraction rate. (source: The Coffee Brewing Handbook by Rob Lingle (SCA, 2011))

Physics-based analysis confirms this priority: hydraulic resistance of a coffee bed is governed primarily by the D₁₀ — the 10th percentile of particle size (the diameter at which 10% of coffee mass by weight is composed of smaller particles). Small particles block water passages far more than large ones open them. This is why improving grind uniformity (reducing fines) has a far greater effect on flow and extraction than removing boulders. See Coffee Bed Hydraulics. (source: The Physics of Filter Coffee by Jonathan Gagné (2020))

Grinder seasoning: New burr sets require ~1–2 kg of coffee to season before delivering a stable particle size distribution. A dial-in established before seasoning is complete will drift coarser as seasoning progresses. (source: The Physics of Filter Coffee by Jonathan Gagné (2020))

Temperature effects on grind: Room temperature shifts the particle size distribution — warmer beans are more ductile and grind coarser. Repeated high-frequency grinding in a short session heats the burrs and similarly shifts the distribution. For maximum repeatability, grind from a consistent starting temperature; grinding from the freezer (single-dose sealed portions) eliminates room temperature effects entirely. (source: The Physics of Filter Coffee by Jonathan Gagné (2020))

Light Roast Grinding Characteristics

This is directly relevant to Kaiserblick’s product:

Light roasts are tenacious, pliable, and tough. They do not break apart as easily as hard, brittle dark roasted beans. As a result:

  • Light roasts always produce fewer fine particles than dark roasts when ground at the same grinder setting
  • Dark roasts are more brittle and will always produce more fines
  • The grinder must therefore be set finer for light roasts to achieve an equivalent particle size distribution
  • Failing to adjust for light roast density → coarser effective grind → under-extraction risk

Additional factors affecting grinding behaviour:

  • Moisture content: Water-quenched beans are softer; air-cooled beans are more brittle and grind better
  • Brittleness: New-crop coffees (less aged) give fewer fines than past-crop; Arabica and Robusta differ; high-grown coffees show different characteristics than lower-altitude coffees
  • Degree of roast: At the same grinder setting, light = tenacious; dark = brittle → always more fines

(source: SCA Coffee Brewing Handbook)

Grind and Extraction Chemistry

Laboratory analysis of brews made at different grind sizes (same temperature, same time) shows:

  • Finer grinds produce higher concentrations of: caffeine, chlorogenic acids, quinic acid, lactic acid
  • Coarser grinds produce higher concentrations of: citric acid, malic acid, acetic acid, fatty acids
  • Controlling grind is the most effective way to manage bitterness and astringency from over-extraction — it is more powerful than adjusting time or temperature alone

Grind size does not significantly affect bitterness and astringency at typical brewing temperatures — this distinction is driven by extraction level, not temperature. (source: SCA Coffee Brewing Handbook)

Factors Influencing Grind Standards

The CBC standardised grinding methodology using a Ro-Tap shaking machine with four Tyler mesh sieves (#10, #14, #20, #28). A 100g sample is shaken for 5 minutes and each sieve fraction weighed. This determines grind class and enables quality control.

For specialty applications, the key principle is that the grind designation must be established for each specific combination of:

  • Coffee product (variety, roast level, origin)
  • Brewing equipment (brewing time, water delivery method)
  • Ambient conditions (especially for espresso)

Grind and Espresso

Espresso grinding is set individually for each specific combination of coffee, machine, and ambient conditions. Espresso requires approximately 500,000 particles per gram — roughly 20 times finer than conventional fine grind. This creates a multi-phase system (solution, emulsion, suspension, foam) with unique extraction dynamics not covered by the standard CBCC framework. (source: SCA Coffee Brewing Handbook)

Burr Quality and Particle-Size Distribution (Espresso Focus)

Scott Rao’s work provides the most detailed analysis of grind quality for espresso. The primary quality indicator is particle-size distribution (PSD): the spread of ground particle sizes around the average. All grinding produces a bimodal distribution — a small peak of very fine particles (fines) and a large peak near the target grind size. A narrower distribution means more grounds close to the target size, fewer fines, and fewer oversized particles (boulders). (source: Espresso Extraction: Measurement and Mastery by Scott Rao (2013))

Fines and Boulders

  • Fines: rapidly overextract → bitterness and astringency; also reduce flow rate by clogging the coffee bed
  • Boulders: underextract → sour, thin; increase flow rate by opening bypass channels

These effects do not cancel out. Any increase in fines + boulders simultaneously (from dull burrs or poor grinder geometry) results in lower net extraction and lower flow rate.

Burr Size

Larger burr sets produce narrower PSDs — fewer fines, fewer boulders. The effect on extraction quality is dramatic:

  • Large, sharp burrs: excellent shots achievable at 21% extraction with minimal bitterness
  • Small burrs: acceptable shots typically limited to 19.5% extraction; above that, bitterness from fines dominates

Larger burrs also impart less heat during grinding and last longer before dulling. The higher initial cost is consistently recovered in bean savings and cup quality. (source: Espresso Extraction: Measurement and Mastery by Scott Rao (2013))

Burr Sharpness

As burrs dull, they create more fines and boulders simultaneously. The net result is always:

  • Lower flow rate
  • Lower extraction
  • More bitterness and astringency (from fines)

Both the maximum achievable extraction and the optimal extraction decrease as burrs dull. Therefore the statement “this coffee tastes best at 19.5%” is only valid for a given burr sharpness; as burrs age, the optimal point shifts downward. Weekly extraction logging with a Coffee Refractometer reveals this trend before the barista can detect it by taste. (source: Espresso Extraction: Measurement and Mastery by Scott Rao (2013))

Doser vs. Doserless Grinders

Doserless grinders (direct-to-portafilter) dispense a variable amount per dose — typically ±1.5 g per shot — because the exit chute holds 4–5 g of grounds that vary between doses. This dosing inconsistency guarantees erratic extraction levels, flow rates, and brewing ratios.

A traditional dosing chamber + grooming protocol achieves ±0.4 g consistency:

  1. Maintain 1–3 g in the dosing chamber before grinding
  2. Grind one dose; pull handle until grounds mound is ~1 g over target
  3. Groom with 7 swipes (N → S → E → W → N → S → N); push excess over basket edge back into chamber
  4. Tamp once at 20–30 lb pressure; do not tap or disturb the puck
  5. Wipe basket rim before inserting

For even higher precision, weigh after grooming and adjust by fractional handle pulls before tamping. (source: Espresso Extraction: Measurement and Mastery by Scott Rao (2013))

Relevance to Kaiserblick

Kaiserblick produces exclusively light roast specialty coffee from high-altitude Salvadoran farms (1,200–1,800 masl). This combination — light roast + high-grown — places their coffee at the more tenacious, harder-to-grind end of the spectrum. Customers (roasters and coffee shops) need to:

  1. Set their grinder finer than for dark roasts to achieve equivalent particle size distribution
  2. Expect fewer fines and adjust dose or brewing time accordingly
  3. Match grind to their specific brewer’s cycle time

This knowledge is a practical value-added service Kaiserblick can provide alongside green coffee sales and roasting services.

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