Kenya Coffee School & Barista Mtaani
Coffee Defects Training Manual & Farmer Handbook
Purpose: This handbook helps farmers, processors, and coffee trainees understand how coffee defects occur and how to prevent them from farm to cup.

  1. Introduction to Coffee Quality
    Coffee quality begins at the farm and continues through harvesting, processing, drying, storage, roasting and brewing.
    Defects occur when mistakes happen at any of these stages.
    Understanding defects helps farmers increase value and helps baristas and buyers protect specialty coffee quality.
  2. What is a Coffee Defect?
    A coffee defect is any physical, chemical, or biological problem that negatively affects coffee appearance, aroma, or flavor.
    Defects can originate from:
  • Farm practices
  • Harvesting methods
  • Processing errors
  • Drying problems
  • Storage conditions
  • Pest damage
  1. Primary Green Bean Defects
    Primary defects significantly reduce coffee quality.
    Examples include:
  • Black beans
  • Sour beans
  • Moldy beans
  • Coffee berry borer damage
  • Severe insect damage
    These defects usually produce strong negative flavors in the cup.
  1. Secondary Green Bean Defects
    Secondary defects affect uniformity and roasting performance.
    Examples include:
  • Broken beans
  • Shell beans
  • Floaters
  • Immature beans
  • Quakers
    These defects reduce consistency and cup balance.
  1. Quakers (Immature Beans)
    Cause:
    Harvesting unripe cherries.
    Identification:
    After roasting, beans remain pale yellow.
    Flavor impact:
    Papery, peanut-like, flat flavor.
    Prevention:
  • Pick only ripe red cherries
  • Sort immature cherries during washing
  1. Stinkers
    Cause:
    Over fermentation or microbial contamination.
    Identification:
    Beans smell rotten when cut.
    Flavor impact:
    Putrid, fermented cup.
    Prevention:
  • Control fermentation time
  • Clean pulping machines
  • Use clean water
  1. Coffee Berry Borer (CBB)
    Scientific name: Hypothenemus hampei
    Damage:
    Insects bore into coffee beans and create tunnels.
    Impact:
    Lower bean weight and poor cup quality.
    Control:
  • Regular harvesting
  • Remove fallen cherries
  • Biological control using Beauveria bassiana
  1. Mold and Fungal Defects
    Cause:
    High humidity during drying or storage.
    Identification:
    White or green mold growth.
    Flavor:
    Musty, earthy, medicinal.
    Prevention:
  • Dry coffee to 10–12% moisture
  • Store in ventilated dry warehouses
  1. Drying Best Practices
  • Use raised drying beds
  • Turn parchment regularly
  • Protect coffee from rain
  • Avoid thick layers during drying
  1. Harvesting Best Practices
  • Pick only ripe red cherries
  • Avoid mixing green and overripe cherries
  • Harvest frequently
  1. Processing Best Practices
  • Clean pulping machines daily
  • Use clean water
  • Control fermentation time
  • Remove floaters
  1. Storage Best Practices
  • Store coffee at 10–12% moisture
  • Use clean dry warehouses
  • Keep bags off the floor
  • Maintain ventilation
  1. Training Exercise for Farmers
    Exercise 1:
    Sort coffee cherries into ripe, underripe and overripe.
    Exercise 2:
    Identify defective beans during drying.
    Exercise 3:
    Cup coffee to detect defects.
  2. Role of Farmers in Specialty Coffee
    Farmers are the first quality controllers in the coffee value chain.
    Proper practices increase coffee prices and protect Kenya’s reputation as a producer of high-quality specialty coffee.