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Screen size grading standards

This topic explains screen size grading standards in coffee milling, how they are measured, why they matter for market classification, and their impact on roasting and flavor consistency.

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Article 3 of 12 in Milling, Sorting & Grading/
Screen size grading standards

What is Screen Size Grading?

  • Screen grading separates green coffee beans by physical size using perforated sieves.
  • Each sieve has holes measured in 1/64 of an inch.
  • Example: Screen 18 = holes of 18/64 inch (7.1 mm).

Common Screen Size Standards

  • Screen 20 (7.94 mm): Extra-large beans (rare, e.g., Maragogipe).
  • Screen 18 (7.14 mm): Large beans, often considered specialty grade.
  • Screen 16 (6.35 mm): Medium-large beans, widely traded.
  • Screen 14 (5.56 mm): Small beans, often lower value.
  • Below 14: Peaberries or defects, usually commercial/low-grade.

Regional Terminology

  • AA, AB, PB (Kenya & Tanzania): Based on screen size categories.
  • SHB (Strictly Hard Bean, Central America): Sometimes combined with size grading.
  • Excelso vs Supremo (Colombia): Supremo = larger screen (17+), Excelso = smaller (14–16).

Why Screen Size Matters

  • Larger beans often correlate with slower maturation and higher quality, though not always.
  • Buyers expect uniform screen sizes for consistent roasting.
  • Mixed sizes cause uneven roasting → under- or over-developed flavors.

Quality & Market Implications

  • Specialty markets: Prefer larger, uniform beans (screen 16+).
  • Commercial markets: More tolerant of mixed screen sizes.
  • Screen grading influences pricing, contracts, and lot classification.

Challenges

  • Screen size is not a perfect predictor of flavor (small beans can still taste excellent).
  • Investment in mechanical graders required for precise sorting.

Best Practices

  • Combine screen grading with density separation for accuracy.
  • Market micro-lots transparently by including screen size data.
  • Document screen distribution in pre-export QA for buyer trust.

Lasting Importance

Screen size grading is a universal language in coffee trade. While not the sole indicator of quality, it provides buyers with a reliable measure of uniformity, supports fair pricing, and improves roasting predictability in specialty and commercial markets.

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Coffee Basics Nerds

Written by : Coffee Basics Nerds

Expert coffee historians and brewing enthusiasts dedicated to sharing the rich heritage and techniques behind your perfect cup of coffee.

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