As we approach the end of the curriculum, we explore the “why” behind coffee traditions, the specifics of Kenyan “Peaberries,” and the ergonomics of a professional coffee bar.
Article 231: The “PB” Grade: Kenya’s Famous Peaberry
(Category: Coffee Bean Knowledge | Word Count: ~280)
In most coffee cherries, two seeds grow side-by-side, creating the familiar flat-sided bean. However, in about 5\% of harvests, only one seed is fertilized. This lone seed grows into a round, pea-shaped bean called a Peaberry (PB).
Why are they famous?
Many coffee professionals believe Peaberries are sweeter and more intense. The theory is that since the tree only had to “feed” one seed instead of two, the flavor is more concentrated.
The Roasting Advantage:
Because they are round, Peaberries roll more easily in the roasting drum. This leads to a very even heat distribution. In Kenya, PB lots are separated and sold as a premium grade. They are known for having a “snappy” acidity and a very concentrated dark-fruit sweetness.
Article 232: Understanding “Water Activity” (aw)
(Category: Coffee Science | Word Count: ~310)
While “Moisture Content” measures the total amount of water in a green bean, Water Activity measures how “bound” or “free” that water is.
Why it matters for storage:
If a green bean has high water activity, the water is “free” to participate in chemical reactions. This leads to:
- Rapid Aging: The coffee will lose its fresh, vibrant flavors and start to taste like “cardboard” or “hay” within months.
- Mold Risk: High water activity allows fungus and bacteria to grow.
The Roasting Impact:
Beans with high water activity require more energy to heat up initially, but they can “take off” and roast uncontrollably fast once they hit higher temperatures. Specialty importers use a “Water Activity Meter” to ensure the Kenyan coffee they buy will stay fresh during its long journey across the ocean.
Article 233: The Ergonomics of the Barista Station
(Category: Barista Skills | Word Count: ~240)
A barista might pull 300 shots in a single shift. Without proper Ergonomics, this leads to “Barista Wrist” (Repetitive Strain Injury).
The Rules of Movement: - The Tamp: Never use your wrist to apply pressure. Your shoulder, elbow, and wrist should form a straight 90^\circ vertical line. You should push down using your body weight and your large shoulder muscles.
- The Portafilter: Keep the portafilter handle close to your body to avoid over-extending your arm.
- The Height: The counter should be at a height where you don’t have to hunch over to see your scales or your latte art.
A healthy barista is a consistent barista. If you are in pain, your technique will suffer, and so will the coffee.
Article 234: What is “Static” Electricity in Grinding?
(Category: Coffee Science | Word Count: ~220)
When coffee is ground, the friction between the burrs creates a massive amount of static electricity. This causes the grounds to clump together and “fly” out of the portafilter.
The Solution: Ionization & RDT: - RDT (Ross Droplet Technique): Adding a tiny mist of water to the beans before grinding to neutralize the charge.
- Ionizers: High-end grinders (like the Mahlkönig EK43) often have built-in ionizers in the chute that use an electric field to remove static as the coffee falls.
Eliminating static isn’t just about cleanliness; it ensures that the “fines” don’t clump together, which leads to a much more even extraction and a clearer flavor profile.
Article 235: The “Golden Ratio” of Brewing
(Category: Brewing Methods | Word Count: ~260)
While everyone has a personal preference, the specialty coffee industry follows a “Golden Ratio” as a starting point for filter coffee. This ratio is typically 1:15 to 1:17.
What does this mean? - 1:15: 1\text{g} of coffee for every 15\text{g} of water (Stronger/Heavier).
- 1:17: 1\text{g} of coffee for every 17\text{g} of water (Lighter/Clearer).
Why we use weight:
If you use a tablespoon, the amount of coffee changes depending on the roast and the grind size. If you use a scale, the ratio is always exact. For a standard mug (300\text{ml} of water), a 1:16 ratio would require 18.7\text{g} of coffee. This balance ensures there is enough water to pull out the sweetness, but not so much that the coffee becomes bitter and over-extracted.
Article 236: The “Center Cut” and Bean Density
(Category: Coffee Bean Knowledge | Word Count: ~210)
Kenyan coffee is famous for being some of the densest in the world. You can see this density by looking at the Center Cut (the line in the middle of the bean).
In high-density beans (grown at high altitudes), the center cut is usually very tight and “zigzagged.” In low-density beans (grown at lower altitudes), the cut is often straight and open.
Why density matters:
Dense beans have a more complex cellular structure. They can withstand higher roasting temperatures without burning, which allows for better sugar development. When you drop a handful of Kenyan AA beans into water, they will sink much faster than lower-quality beans—a physical sign of the concentrated flavor inside.
Article 237: The History of the “Long Black”
(Category: Barista Skills | Word Count: ~230)
While an Americano is espresso with water added on top, a Long Black (popular in Australia and New Zealand) is the reverse: espresso pulled directly onto hot water.
The Difference:
By pulling the espresso onto the water, the crema remains intact on the surface. This preserves the aromatic oils and gives the drink a much stronger aroma and a “heavier” mouthfeel than a standard Americano.
Barista Tip: Use water that is around 70^\circ\text{C} to 80^\circ\text{C}. If the water is boiling, it will “scald” the espresso and destroy the delicate fruity notes of a specialty Kenyan bean.
Article 238: The Impact of “Atmospheric Pressure”
(Category: Coffee Science | Word Count: ~250)
Did you know that coffee brews differently in Nairobi (1,795\text{m} altitude) than it does in Mombasa (sea level)? This is due to Atmospheric Pressure.
The Boiling Point:
At sea level, water boils at 100^\circ\text{C}. In the high altitudes of the Kenyan coffee lands, water boils at around 94^\circ\text{C} to 95^\circ\text{C}.
The Extraction Shift:
Because you cannot get water hotter than its boiling point in an open kettle, baristas in high-altitude regions have to grind their coffee finer or brew for longer to achieve the same extraction as someone at sea level. If you take a recipe from a London coffee shop and try it in Nairobi, it will likely taste under-extracted and sour!
Article 239: Understanding “Oxidation” in Roasted Coffee
(Category: Coffee Education | Word Count: ~220)
Oxygen is the greatest enemy of roasted coffee. The moment beans leave the roaster, they begin to Oxidize.
The Chemical Reaction:
Oxygen reacts with the delicate lipids (oils) in the coffee, turning them rancid. This creates the “stale” flavor that tastes like old peanuts or wet cardboard. - Whole Beans: Have a “shelf life” of about 4 weeks before oxidation becomes noticeable.
- Ground Coffee: Because of the increased surface area, ground coffee can oxidize and lose its sweetness in as little as 15 minutes.
This is why we always emphasize: Grind only what you need, exactly when you need it.
Article 240: The “Milk-to-Coffee” Balance
(Category: Sensory Skills | Word Count: ~290)
In a café, we often spend all our time focusing on the espresso, but 80\% of customers drink milk-based beverages. The balance between the two is a science. - The Small Drink (Macchiato/Piccolo): The espresso is the star. The milk is just there to add a hint of sweetness.
- The Medium Drink (Flat White/Cappuccino): The “Sweet Spot.” Here, the milk should transform the espresso into something that tastes like melted chocolate or caramel, but you should still be able to taste the coffee’s origin.
- The Large Drink (Latte): The milk is the dominant flavor.
If you use a very delicate, floral Kenyan coffee in a large 12oz Latte, the flavor will be “drowned” by the milk. For large milk drinks, we typically use a more “punchy,” darker-roasted coffee so the flavor can cut through the fat of the milk.