Kenya Coffee School

From Seed to Cup – Barista Skills & Specialty Coffee

Revision Questions and Answers

Part 3: Questions 41–60 (Grinding, Brewing & Espresso)

41. Why is grind size important?

Answer: Grind size controls how quickly water extracts soluble compounds from coffee. It directly affects flavour, aroma, strength, and extraction time.

Explanation:

• Fine grind = slower water flow and more extraction.
• Coarse grind = faster water flow and less extraction.

Exam Tip: Adjust the grind before changing other brewing variables.

42. Match brewing methods with grind sizes.

Answer:

Explanation: Each brewing method requires a specific grind to achieve balanced extraction.

Exam Tip: Incorrect grind size is one of the most common causes of poor coffee.

43. Explain brew ratio.

Answer: A brew ratio is the relationship between the amount of coffee and the amount of water used during brewing.

Example:

• 1:15 = 1 g coffee to 15 g water
• 1:16 = Common filter coffee ratio
• Espresso often uses a ratio around 1:2 (e.g., 18 g coffee produces 36 g espresso).

Explanation: The brew ratio influences coffee strength and balance.

Exam Tip: Always measure coffee and water with a digital scale for consistency.

44. What is extraction?

Answer: Extraction is the process of dissolving desirable flavour compounds from ground coffee into water.

Explanation: Proper extraction creates a balanced cup with sweetness, pleasant acidity, and body.

Exam Tip: Aim for balanced extraction—not too little and not too much.

45. What causes under-extraction?

Answer: Under-extraction may result from:

• Grind too coarse
• Water temperature too low
• Brew time too short
• Too little coffee
• Uneven extraction

Explanation: Under-extracted coffee often tastes sour, weak, or grassy.

Exam Tip: Sour coffee usually indicates under-extraction.

46. What causes over-extraction?

Answer: Over-extraction may result from:

• Grind too fine
• Water too hot
• Brew time too long
• Excessive agitation

Explanation: Over-extracted coffee tastes bitter, harsh, and dry.

Exam Tip: Bitter coffee often indicates over-extraction.

47. State the ideal brewing water temperature.

Answer: The recommended brewing temperature is 90–96°C.

Explanation: Water below 90°C may under-extract coffee, while water above 96°C can increase bitterness.

Exam Tip: The ideal target for many brews is around 93°C.

48. Why is water quality important?

Answer: Water makes up about 98% of brewed coffee, so its quality has a major impact on flavour.

Good brewing water should:

• Be clean and odour-free
• Have balanced mineral content
• Be free from contaminants

Explanation: Poor-quality water can mask or distort coffee flavours.

Exam Tip: Great coffee starts with great water.

49. Explain Total Dissolved Solids (TDS).

Answer: TDS measures the concentration of dissolved substances in water or brewed coffee.

Explanation: For brewing water, an appropriate mineral content supports proper extraction and flavour.

Exam Tip: Water with extremely low or high TDS can negatively affect coffee quality.

50. Define coffee strength.

Answer: Coffee strength refers to the concentration of dissolved coffee solids in the beverage.

Explanation: Strength is different from flavour quality. A coffee can be strong but poorly extracted, or mild but well balanced.

Exam Tip: Do not confuse strength with bitterness.

Espresso

51. What pressure is used in espresso extraction?

Answer: The standard brewing pressure is approximately 9 bars.

Explanation: This pressure forces hot water through finely ground coffee to produce espresso.

Exam Tip: Most commercial espresso machines are calibrated to brew at around 9 bars.

52. What is the ideal espresso extraction time?

Answer: Generally 25–30 seconds, depending on the coffee and recipe.

Explanation: A properly extracted espresso should have balanced sweetness, acidity, and body.

Exam Tip: Extraction time alone is not enough—always taste the espresso.

53. What is crema?

Answer: Crema is the golden-brown foam that forms on top of a freshly brewed espresso.

Explanation: It is created when carbon dioxide and coffee oils emulsify under pressure.

Exam Tip: Good crema indicates fresh coffee and proper extraction but is not the only indicator of quality.

54. What is channeling?

Answer: Channeling occurs when water finds weak paths through the coffee puck instead of extracting it evenly.

Explanation: This results in uneven extraction, causing sourness and bitterness in the same shot.

Exam Tip: Good distribution and even tamping help prevent channeling.

55. Name the main parts of an espresso machine.

Answer:

• Group head
• Portafilter
• Filter basket
• Steam wand
• Boiler
• Pump
• Water reservoir or water inlet
• Pressure gauge
• Hot water outlet
• Drip tray

Explanation: Each component plays a role in producing consistent espresso.

Exam Tip: Learn both the names and functions of these parts.

56. Explain pre-infusion.

Answer: Pre-infusion is the gentle wetting of the coffee puck before full brewing pressure is applied.

Explanation: It helps reduce channeling and improves extraction uniformity.

Exam Tip: Many modern espresso machines include programmable pre-infusion.

57. Why is tamping important?

Answer: Tamping compresses the coffee grounds into an even puck, allowing water to flow uniformly.

Explanation: Uneven tamping can lead to channeling and inconsistent espresso.

Exam Tip: Press straight and level with consistent pressure.

58. What is puck preparation?

Answer: Puck preparation includes:

• Grinding
• Dosing
• Even distribution
• Level tamping
• Cleaning the portafilter rim

Explanation: Proper puck preparation improves extraction consistency.

Exam Tip: Most espresso problems begin with poor puck preparation.

59. Define dose, yield, and ratio.

Answer:

• Dose: Amount of dry coffee placed in the portafilter.
• Yield: Weight of liquid espresso produced.
• Ratio: Relationship between the dose and yield.

Example: 18 g coffee → 36 g espresso = 1:2 brew ratio.

Explanation: These measurements help baristas produce repeatable espresso.

Exam Tip: Always use a digital scale instead of guessing.

60. Explain espresso dialing in.

Answer: Dialing in is the process of adjusting brewing variables to achieve the best espresso flavour.

Variables include:

• Grind size
• Dose
• Yield
• Extraction time
• Water temperature

Explanation: Baristas dial in espresso at the start of the day and whenever coffee or environmental conditions change.

Exam Tip: Only adjust one variable at a time, then evaluate the result before making further changes.

End of Part 3

In Part 4 (Questions 61–80), you will revise:

• Milk Science
• Milk Steaming
• Latte Art
• Alternative Milks
• Café Hygiene
• Food Safety
• Customer Service
• Inventory Management
• Opening and Closing Procedures

This section is essential for practical barista training and specialty café operations at Kenya Coffee School.