This set focuses on technical maintenance, historical context, and the subtle “dark” arts of roasting and sensory evaluation.
Article 211: The Physics of “Grind Retention”
(Category: Barista Skills | Word Count: ~280)
Grind Retention refers to the coffee that gets trapped inside the grinder’s internal chambers between the burrs and the exit chute.
Why it matters:
If a grinder has 5\text{g} of retention, and you change the grind size from “coarse” to “fine,” the next shot you pull will contain 5\text{g} of the old, coarse coffee mixed with the new, fine coffee. This results in an “in-between” extraction that won’t taste right.
The Professional Solution:
To avoid this, baristas perform a Purge. They grind a small amount of coffee (roughly the amount the grinder retains) and discard it. In modern “Single Dose” grinders, engineers use blowers or vertical chutes to achieve “Zero Retention,” ensuring that what you put in is exactly what you get out.
Article 212: Understanding “Chlorogenic Acids”
(Category: Coffee Science | Word Count: ~310)
Chlorogenic Acids (CGA) are a family of antioxidant compounds found in high concentrations in green coffee. They are the primary source of bitterness and “astringency” in the bean.
The Transformation:
During roasting, CGAs break down into Quinic Acid and Caffeic Acid.
- Light Roasts: Retain more CGAs, which can sometimes result in a metallic or “herbal” taste if not handled correctly.
- Dark Roasts: Most CGAs are destroyed, but they are replaced by Quinic Acid, which contributes to the “stale” or “burnt” bitterness often associated with low-quality dark roasts.
For a Kenyan coffee, the roasting goal is to hit the “sweet spot” where CGAs have broken down enough to lose their metallic edge, but haven’t yet turned into the harsh bitterness of Quinic acid. This balance allows the fruity citric and malic acids to shine.
Article 213: The “T-Grade” and “TT-Grade”
(Category: Coffee Bean Knowledge | Word Count: ~230)
In the Kenya grading system, T and TT represent the smallest and lightest beans. - T: These are the smallest beans, often fragments or very thin seeds that fall through the size 12 screen.
- TT: These are the “light” beans that are blown away from the AA, AB, and C grades by air separators. They are often less dense or have internal hollows.
Commercial Use:
While you won’t usually find T or TT grades in a specialty coffee bag, they are highly sought after by large commercial manufacturers. They are used in instant coffee production or pre-ground “supermarket” blends. Because they are thin and light, they roast very quickly, making them efficient for high-volume, low-cost coffee production.
Article 214: The “3-Second Rule” of Latte Art
(Category: Barista Skills | Word Count: ~190)
Timing is everything in latte art. The 3-Second Rule refers to the window of time between finishing your milk steaming and beginning your pour.
If you wait too long (more than 3 seconds), the milk and foam will begin to separate in the pitcher. The liquid milk sinks to the bottom, and the foam floats to the top. When you try to pour, you will get a “clump” of white foam at the end rather than a smooth, integrated design.
The Fix: If you are forced to wait (e.g., waiting for the espresso to finish), keep the milk “alive” by continuously swirling the pitcher in a gentle circular motion until the moment you are ready to pour.
Article 215: Why Kenyan Soil is Special: Volcanic Ash
(Category: Coffee Education | Word Count: ~290)
Most of Kenya’s best coffee is grown in the “Central Highlands,” in the shadow of Mount Kenya and the Aberdare Ranges. This land is rich in Nitisol, a deep, red volcanic soil.
Why it’s perfect for coffee: - Drainage: Volcanic soil is very porous, allowing water to reach deep roots without “drowning” the plant.
- Mineral Wealth: It is naturally rich in iron and aluminum, which contribute to the bean’s density and the development of those famous “bright” organic acids.
- Depth: In Nyeri and Kirinyaga, the volcanic soil can be several meters deep, allowing the coffee tree’s taproot to reach nutrients that have been stored for centuries.
When we talk about the “Terroir” of Kenya, we are mostly talking about the unique mineral signature of this ancient volcanic ash.
Article 216: The “Center Cut” and Roast Degree
(Category: Roasting Knowledge | Word Count: ~210)
The “Center Cut” is the crease that runs down the middle of the coffee bean. For a barista, it is a visual indicator of how the coffee was roasted. - Light/Medium Roast: The center cut will often still have white or tan “chaff” (the silver skin) trapped inside. The bean itself will look expanded and open.
- Dark Roast: The center cut will look dark and may even be “charred.” As the bean expands more aggressively in high heat, the crease often widens and becomes oily.
By looking at the center cut, a barista can guess the “solubility” of the bean. If the crease is tight and white, the coffee likely needs hotter water and more agitation to extract properly.
Article 217: What is “Astringency”?
(Category: Sensory Skills | Word Count: ~220)
Astringency is often confused with bitterness, but it is actually a mouthfeel, not a taste. It is the dry, puckering sensation you get after eating an unripe banana or drinking very strong tea.
The Cause:
Astringency is caused by Polyphenols (tannins) binding to the proteins in your saliva. This “sandpaper” feeling on the tongue usually indicates one of two things in coffee: - Under-ripe beans: The cherries were picked before the sugars could mask the tannins.
- Over-extraction: The water was in contact with the coffee for too long, pulling out the woody, dry compounds from the bean’s structure.
A perfect Kenyan coffee should be “juicy,” meaning it has zero astringency and leaves your mouth feeling hydrated, not dry.
Article 218: The “Turkish Coffee” Method
(Category: Brewing Methods | Word Count: ~270)
Turkish coffee (Cezve/Ibrik) is the oldest brewing method still in common use. It is unique because the coffee is not filtered at all.
The Technique: - The Grind: It must be an “impalpable powder”—even finer than espresso. It should feel like flour.
- The Brew: Coffee, water, and often sugar are heated in a copper pot. As it nears boiling, a thick “foam” (the kaimaki) rises to the top.
- The Serve: The coffee is poured, grounds and all, into small cups. You must wait 2 minutes for the grounds to settle at the bottom before drinking.
While very different from “Third Wave” filter coffee, the Turkish method produces an incredible intensity of flavor. In Kenya, this method is popular in coastal regions like Mombasa, often spiced with cardamom.
Article 219: Maintaining the “Shower Screen”
(Category: Barista Skills | Word Count: ~180)
The Shower Screen is the metal mesh plate inside the group head that disperses water onto the coffee puck.
If you don’t scrub the screen with a brush every hour, coffee oils and “fines” will clog the tiny holes. This causes the water to come out in “jets” rather than a gentle mist. This leads directly to Channelling, as the high-pressure jets of water blast holes in your coffee puck.
The Pro Tip: At least once a week, use a screwdriver to remove the screen and soak it in detergent. You will be amazed at how much better your espresso tastes when the water can flow freely!
Article 220: The “Body” vs. “Intensity” Debate
(Category: Sensory Skills | Word Count: ~250)
In barista training, students often confuse Body with Intensity. - Intensity: Refers to the “strength” of the flavors. A shot of espresso is very intense; a cup of filter coffee is less intense.
- Body: Refers to the “weight” or “texture.” A French Press has a heavy body (oil/sediment); a V60 has a light, tea-like body.
The Kenyan Example:
Kenyan coffee is famous because it can be highly intense (punchy acidity/flavor) while still having a medium, juicy body. It doesn’t need to be “thick” like a Brazilian coffee to be powerful. Learning to describe these two things separately is key to passing your sensory exams.