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Sampling for moisture and a-w

This topic explains how to properly sample coffee for measuring moisture content and water activity (a-w), why representative sampling is critical, and how these tests ensure stability and quality.

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  • Coffee Basics Nerds
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Article 8 of 12 in Drying, Conditioning & On-Farm Storage/
Sampling for moisture and a-w

Why Sampling Matters

  • Coffee beans dry unevenly across beds, bags, or warehouses.
  • Taking representative samples prevents false readings.
  • Ensures coffee is within the safe range: 10–12% moisture and 0.55–0.65 a-w.

Moisture Sampling

  • Tools: Handheld moisture meters.
  • Method:
  • Take beans from multiple locations (top, middle, bottom of bags or piles).
  • Mix samples to create a composite for testing.
  • Calibrate meters regularly to maintain accuracy.

Water Activity (a-w) Sampling

  • Tools: Water activity meters (more precise, lab-grade).
  • Method:
  • Seal beans in the chamber of the device.
  • Device measures vapor pressure equilibrium.
  • Readings confirm microbial stability (<0.65).

Best Practices for Sampling

  1. Frequency: Check at drying beds, before storage, and periodically during storage.
  2. Lot separation: Sample each lot individually to maintain traceability.
  3. Composite approach: Combine multiple small samples for representative results.
  4. Avoid bias: Don’t sample only surface beans—include deeper layers.

Risks of Poor Sampling

  • Overestimation: Leads to under-dried beans → mold risk.
  • Underestimation: Leads to over-drying → brittle beans, flavor loss.
  • Misleading results can cause rejection at export or roasting.

Market Relevance

  • Specialty buyers often request documented moisture and a-w readings.
  • Certifications may require proof of sampling protocols.
  • Data adds credibility, showing commitment to quality.

Lasting Importance

Sampling for moisture and a-w is a critical quality control step in drying and storage. Proper representative sampling ensures coffee is safe, stable, and high-quality, protecting both flavor integrity and farmer reputation in specialty 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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