What are Coffee Bean Sizes and Standards S12, S13, S14, S15, S16, S17, S18?

coffee screen size vnph pacific

What are Coffee Bean Sizes and Standards S12, S13, S14, S15, S16, S17, S18?

In the coffee industry, sorting beans by size is a crucial step to ensure even roasting. If you’re exploring green coffee beans, you’ve likely encountered terms like S16 or S18. Below is a detailed explanation of the terminology, symbols, and how to convert coffee bean sizes according to international standards.

1. What does the "S" Symbol and Screen Standard Mean?

In coffee trading, the letter “S” stands for “Screen”. The numbers following the “S” (like 12, 13, 16, 18, etc.) represent the diameter of the screen’s holes, calculated in 64ths of an inch. According to this standard, 1 inch equals 25.4 mm. This system uses metal screen plates with multiple perforated holes to filter and sort coffee beans from large to small uniformly.

coffee size s16, s18 vnph pacific
2. Detailed Coffee Bean Sizes

Based on the international standard classification system, we can convert common bean sizes into millimeters (mm) as follows:

  • S18: Equivalent to a screen hole size of 18/64 inch (about 7.1 mm). This is typically a large, high-quality bean and is considered the largest size for common Arabica and Robusta varieties on the market.
  • S17: Equivalent to a screen hole size of 17/64 inch (about 6.75 mm). 
  • S16: Equivalent to a screen hole size of 16/64 inch (about 6.3 mm).
  • S15: Equivalent to a screen hole size of 15/64 inch (about 5.95 mm). 
  • S14: Equivalent to a screen hole size of 14/64 inch (about 5.6 mm).
  • S13: Equivalent to a screen hole size of 13/64 inch (about 5.0 mm).
  • S12: Equivalent to a screen hole size of 12/64 inch (about 4.76 mm). In standard commercial transactions, S12 or S13 is usually the smallest threshold for standard green coffee beans.
3. What are the Smallest and Largest Screen Sizes?

According to international standards, screen sizes typically range from S8 to S20, and occasionally up to S22.

  • Smallest Sizes (S8 – S10): The S8 screen has a hole size of 8/64 inch (about 3.17 mm). Screens from S8 to S10 are usually only used to sort very small peaberry beans, or to filter out broken or defective beans. 
  • Largest Sizes (S20 – S22): Extra-large screen holes can reach 20/64 or 22/64 inch (about 7.9 – 8.7 mm). Screens of this size are primarily used for rare coffee varieties with giant beans, such as Maragogype or Pacamara.
4. The Importance of Sorting by Screen Size

Using a uniform bean size (e.g., 100% S18 or S16) helps roasters control temperatures more evenly. If a roast is a mix of large and small beans, the small beans risk being burnt and bitter, while the large beans may remain under-roasted inside, resulting in a sharp, sour taste. Size uniformity through accurate screens is the key to creating perfect roasts and extracting the original flavor of the coffee beans.

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