This batch focuses on the chemistry of roasting, espresso machine components, and the tactile skills of a barista.
Article 111: The “Second Crack” in Roasting
(Category: Roasting Knowledge | Word Count: ~260)
While the “First Crack” sounds like popcorn and signifies a light roast, the Second Crack is much quieter and faster, sounding like the snapping of dry twigs or “Rice Krispies.”
What is happening?
The Second Crack is a physical fracturing of the bean’s cellular matrix. By this stage, the bean has become very brittle and dry. The internal pressure of carbon dioxide and the expansion of oils become too much, causing the wooden fibers of the bean to actually snap.
The Flavor Shift:
- Beyond the Bean: At this point, the “origin” flavors (the fruity, floral notes) are mostly destroyed by heat.
- Roast Flavors: The taste is now dominated by the roasting process itself—expect notes of dark chocolate, smoke, carbon, and intense bitterness.
- Oils: This is the stage where oils are forced to the surface, giving the beans a shiny, greasy appearance.
For specialty coffee, most roasters stop well before the Second Crack to preserve the unique character of the coffee’s origin.
Article 112: The Solenoid Valve: The Unsung Hero
(Category: Barista Skills | Word Count: ~230)
Have you ever wondered why the pressure in an espresso machine drops instantly the moment you turn off the pump? This is thanks to the 3-way Solenoid Valve.
How it Works:
When you start a shot, the valve opens a path from the boiler to the group head. When you stop the shot, the valve does two things simultaneously: - It shuts off the water flow from the pump.
- It opens a “vent” that leads to the drip tray.
The Result:
This sudden opening “sucks” the excess pressure and water away from the coffee puck. This is what creates a dry, firm coffee puck that is easy to knock out. Without this valve, the pressure would stay trapped in the portafilter, and if you tried to remove it, you would experience a “portafilter sneeze”—a messy explosion of hot coffee grounds and water.
Article 113: Understanding “Coffee Tides” (The Flow Rate)
(Category: Barista Skills | Word Count: ~210)
In barista training, we often talk about the “look” of the espresso flow. This is sometimes called the “Mouse Tail” because of its thin, curved shape.
The Stages of Flow: - The Drip: The first few seconds should be dark, viscous droplets.
- The Stream: The droplets merge into a steady, thin stream.
- The Color Shift: The stream starts dark brown, then turns to a rich “tiger-striped” gold.
- The Blonding: Finally, the stream becomes pale and watery (blonding), signaling the end of the extraction.
If the flow starts too quickly (like an open tap), your grind is too coarse. If it only drips slowly for 30 seconds, your grind is too fine. Learning to “read” the flow by eye is a vital skill for a barista when they don’t have a scale available.
Article 114: The Impact of Humidity on Grinding
(Category: Barista Skills | Word Count: ~280)
Experienced baristas know that the “dial-in” from 8:00 AM rarely works by 2:00 PM. The biggest reason for this is humidity.
The Science:
Roasted coffee beans are hygroscopic—they act like tiny sponges that absorb moisture from the air. - High Humidity: The beans absorb moisture and swell. This makes them “softer” and causes them to shatter into more “fines” in the grinder. This usually slows down the espresso flow.
- Low Humidity (Dry Air): The beans are more brittle and grind more cleanly, but static electricity increases, which can cause the grounds to clump and “spray” out of the grinder.
The Barista’s Adjustment:
On a rainy day in Nairobi, you will likely need to coarsen your grind to compensate for the humidity. On a very dry, hot day, you may need to go finer. This is why “dialing in” is a constant, all-day process, not a one-time task.
Article 115: What is “Gully” or “Wild” Coffee?
(Category: Coffee Education | Word Count: ~250)
In the Kenyan context, you may sometimes hear about “Wild” or “Gully” coffee. This refers to coffee trees that have grown outside of organized plantations, often from seeds dropped by birds or monkeys.
The Quality Gap:
While the idea of “wild” coffee sounds romantic, it is rarely specialty grade. - Lack of Pruning: These trees are often overgrown, meaning the plant’s energy is spread thin across too many branches, resulting in small, nutrient-deficient cherries.
- Pest Issues: Without the care of a farmer, these trees are often infested with the Coffee Berry Borer or Leaf Rust.
- Genetic Mystery: You don’t know if the tree is an SL28, a Ruiru 11, or an older, lower-quality variety.
While these trees are part of Kenya’s rich coffee landscape, the specialty industry relies on the cultivated and meticulously cared-for trees found in cooperatives and estates.
Article 116: The Heat Exchanger vs. Dual Boiler
(Category: Coffee Business | Word Count: ~320)
When buying an espresso machine for a café, the internal heating system is the most important spec.
- Heat Exchanger (HX):
There is only one large boiler used for steam. A small pipe (the heat exchanger) runs through this boiler to heat the brew water.
- Pros: Cheaper and very powerful for steaming.
- Cons: The brew water can get too hot if the machine sits idle. You must perform a “cooling flush” before every shot.
- Dual Boiler:
The machine has two separate boilers—one for steam and one for brewing.
- Pros: Ultimate temperature stability. You can set the brew boiler to exactly 93.5^\circ\text{C} and it will stay there all day.
- Cons: More expensive and takes longer to heat up initially.
For a high-volume specialty café where consistency is the goal, a Dual Boiler machine is almost always the better investment. It removes the guesswork of temperature management for the barista.
Article 117: Mastering the “Rosetta” Latte Art
(Category: Barista Skills | Word Count: ~290)
The Rosetta is the classic symbol of a specialty coffee shop. It looks like a fern or a leaf and requires a high level of coordination.
The Technique: - The Swing: Start with the pitcher close to the surface and begin a steady side-to-side “wiggle” or “swing” with your wrist. This creates the base petals.
- The Retreat: As you continue the wiggle, slowly move the pitcher toward the back of the cup. This creates the “leaves” of the fern.
- The Top: As you reach the top of the cup, stop the wiggle to create a small heart at the tip.
- The Cut: Lift the pitcher high and draw a thin line of milk straight through the center back toward the bottom. This creates the “stem” and pulls the leaves into the classic Rosetta shape.
The key to a good Rosetta is rhythm. If your wiggle is too fast, the leaves will be blurred; if it is too slow, the design will look blocky.
Article 118: Why We Use “Raised Beds” Instead of Patios
(Category: Coffee Education | Word Count: ~230)
While many countries dry coffee on large concrete patios, Kenya is famous for its wooden or metal raised beds.
The Advantage of Height: - 360-Degree Drying: On a patio, only the top of the bean is exposed to the air. On a raised bed, the mesh bottom allows air to flow underneath the beans. This dries the coffee twice as fast and much more evenly.
- Cleanliness: It keeps the coffee away from dust, animals, and soil contamination.
- Back Health: It is much easier for workers to sort through the parchment coffee while standing at a bed than it is while stooping over a patio.
This method is more expensive to build, but it is a cornerstone of why Kenyan coffee is so clean and free of the “earthy” defects often found in patio-dried coffees.
Article 119: The “Dead Shot” Myth
(Category: Barista Skills | Word Count: ~210)
There is a common myth in the coffee world that an espresso shot “dies” if it sits for more than 30 seconds. Some people claim the crema “rottenizes” and the shot becomes bitter.
The Truth:
A shot doesn’t “die,” but it does change. - Temperature: As the shot cools, our tongues can actually perceive more flavor. A piping hot shot often hides its complexity behind the heat.
- Oxidation: The crema will eventually dissolve and the aromatics will fade, but this takes several minutes, not seconds.
- Bitterness: The shot might seem more bitter as it cools because our taste buds are more sensitive to bitterness at lower temperatures.
As a barista, don’t panic if a shot sits for 40 seconds while you steam milk. However, for the best customer experience, you should always aim to serve the drink as fresh as possible while the aromatics are at their peak.
Article 120: The Role of the “Marketing Agent” in Kenya
(Category: Coffee Business | Word Count: ~300)
In the Kenyan coffee value chain, the Marketing Agent plays a critical role in connecting the farmer to the global market.
Their Responsibilities: - Representation: They act on behalf of the cooperative or estate at the Nairobi Coffee Exchange (NCE).
- Sample Distribution: They prepare small “sample bags” of a lot and distribute them to all the licensed coffee exporters and buyers.
- Price Advice: They advise the farmers on whether to accept a bid at the auction or to “withdraw” the coffee and wait for a better price next week.
- Liquidation: Once the coffee is sold, they handle the paperwork to ensure the money flows back from the buyer to the cooperative’s bank account.
The Marketing Agent is the bridge between the agricultural world of the farm and the financial world of the auction. Choosing a reputable agent is one of the most important business decisions a Kenyan coffee cooperative can make.