Farm → Factory → Mill → Roastery → Cup

Author: Alfred Gitau Mwaura

PART 12: ADVANCED COFFEE DEFECTS

Understanding advanced defects is important for professional cuppers and roasters because some defects cannot be detected visually but appear only in the cup.

26. Baggy Defect

Baggy flavor occurs when green coffee absorbs odors from storage materials.

Causes

Poor warehouse storage conditions such as:

• Old jute bags
• Chemical contamination
• Damp warehouses
• Poor ventilation

Sensory Characteristics

Baggy coffee may taste:

• Sack-like
• Woody
• Flat
• Stale

Baggy coffee loses its fresh aromatic character.

27. Woody Defect

Woody flavor typically develops when coffee is too old or stored improperly.

Causes

• Long storage periods
• High humidity storage
• Oxygen exposure

Sensory Characteristics

Woody coffee may taste like:

• Dry wood
• Paper
• Cardboard

The coffee loses acidity and sweetness.

28. Earthy Defect

Earthy flavor occurs when coffee is contaminated with soil or microbes.

Causes

• Coffee dried directly on soil
• Poor washing
• Microbial contamination

Sensory Characteristics

Earthy coffee tastes like:

• Wet soil
• Damp forest floor
• Mushrooms

29. Phenolic Defect

Phenolic defects are caused by bacterial contamination during fermentation.

Causes

• Dirty fermentation tanks
• Poor hygiene
• Contaminated water

Sensory Characteristics

Phenolic coffee may taste like:

• Medicine
• Plastic
• Chemical flavor

30. Smoky Defect

Smoke contamination occurs when coffee is dried near smoke sources.

Causes

• Firewood drying systems
• Smoke exposure during drying

Sensory Characteristics

Coffee may taste like:

• Smoke
• Burnt wood
• Charcoal

PART 13: POTATO TASTE DEFECT (PTD)

Potato Taste Defect is one of the most serious defects affecting East African coffee.

PTD is common in:

• Rwanda
• Burundi
• Uganda
• Parts of Western Kenya

31. What Causes PTD

PTD is associated with:

• Bacterial contamination
• Insect damage

Researchers have linked PTD to bacteria carried by insects such as Antestia bugs.

32. Chemical Compounds in PTD

The potato smell comes from a compound called:

Isopropyl Methoxypyrazine (IPMP)

This compound produces the smell of:

• Raw potatoes
• Green vegetables

Even extremely small concentrations can produce strong odor.

33. PTD Detection

PTD is difficult to detect visually.

Detection methods include:

• Roasting sample beans
• Grinding beans
• Smelling the aroma immediately

Professional cuppers can detect PTD quickly.

PART 14: COFFEE CUPPING SYSTEM

Coffee cupping is the standardized method used to evaluate coffee quality.

34. Cupping Equipment

Professional cupping requires:

Cupping bowls
Cupping spoons
Coffee grinder
Hot water kettle
Scale
Timer

35. Standard Cupping Protocol

Typical cupping protocol includes:

Coffee dose: 8.25 grams
Water: 150 ml
Water temperature: 93°C

36. Cupping Procedure

Steps include:

1 Grind coffee
2 Smell dry fragrance
3 Add hot water
4 Break crust after 4 minutes
5 Smell aroma
6 Taste coffee

37. Sensory Evaluation Criteria

Cuppers evaluate:

Fragrance
Aroma
Flavor
Aftertaste
Acidity
Body
Balance
Sweetness
Uniformity
Clean cup

PART 15: COFFEE ROASTING AND DEFECT DETECTION

Roasting reveals many defects hidden in green coffee.

38. Roast Chemistry

Roasting involves several chemical reactions.

Key reactions include:

Maillard Reaction

Produces:

• caramel notes
• nutty flavors

Caramelization

Occurs when sugars break down during roasting.

Creates:

• sweetness
• caramel flavors

Pyrolysis

Breakdown of organic compounds at high temperatures.

Produces:

• smoky flavors
• roast aromas

39. Roast Defects

Common roasting defects include:

Underdevelopment

Coffee tastes:

• grassy
• sour

Over-roasting

Coffee tastes:

• burnt
• bitter

Uneven roasting

Caused by inconsistent bean density.

PART 16: GREEN COFFEE GRADING

Coffee grading is used to determine coffee quality before export.

40. Kenya Coffee Bean Grades

Kenyan coffee is graded by bean size.

Common grades include:

AA
AB
PB (Peaberry)
C
TT

41. Defect Count Method

Coffee quality is also measured by counting defects.

Each defect has a defect value.

Example:

1 black bean = major defect
5 broken beans = minor defect

Coffee is graded based on total defect count.

PART 17: COFFEE ECONOMICS AND DEFECTS

Defects reduce coffee market value.

Higher defect levels result in:

Lower auction prices
Lower export value
Reduced farmer income

42. Specialty Coffee Standards

Specialty coffee typically requires:

Defect-free green beans
Excellent cup profile
High cupping score

Specialty coffees often score 80 points or higher.

PART 18: QUALITY TRAINING FOR FARMERS

Improving coffee quality begins with farmer education.

Key training topics include:

Selective harvesting
Processing hygiene
Proper drying
Defect identification

43. Field Training Demonstrations

Barista Mtaani farmer trainings include:

Cherry selection training
Drying bed management
Coffee cupping workshops

PART 19: BUILDING A COFFEE QUALITY CULTURE

Improving coffee quality requires building a culture of:

Attention to detail
Continuous training
Transparency in the value chain

44. The Mission of Kenya Coffee School

Kenya Coffee School exists to:

Train farmers
Train baristas
Promote coffee innovation
Strengthen the Kenyan coffee brand globally

Final Reflection

Coffee defects are not just technical issues.

They reflect the health of the entire coffee ecosystem.

When farmers, processors, roasters, and baristas understand coffee defects, they gain the power to protect quality, increase income, and sustain the coffee industry.

Through education, innovation, and community empowerment, Kenya Coffee School and Barista Mtaani are helping build a stronger future for Kenyan coffee.