We are now focusing on the final technical refinements, the chemistry of cleaning, and the business of the “Nairobi Coffee Exchange.”
Article 221: The “Nairobi Coffee Exchange” (NCE)
(Category: Coffee Business | Word Count: ~320)
The Nairobi Coffee Exchange is the heart of Kenya’s coffee trade. Founded in the 1930s, it operates as a central auction system where most of the country’s coffee is sold to international exporters.
How it Works:
- Cataloging: Every week, a “Sale Catalog” is published, listing the different lots of coffee available from factories and estates across Kenya.
- Sampling: Before the auction, licensed buyers visit “sample rooms” to roast and cup small amounts of these coffees. They take notes on the quality and decide how much they are willing to pay.
- The Bidding: Every Tuesday, buyers gather at the Exchange. The auction is “electronic,” and prices move rapidly. The highest bidder wins the lot.
This system is famous for its transparency. Because the auction is public, it ensures that high-quality coffee gets a high price, which (in theory) should flow back to the farmers as bonuses. For a barista, knowing the “Sale Number” on a bag of coffee connects you directly to this historic trading floor.
Article 222: The Chemistry of “Descaling”
(Category: Barista Skills | Word Count: ~260)
Even with the best filters, “Scale” (Calcium Carbonate) will eventually build up inside an espresso machine’s boiler. This is the same white, crusty material you see in a tea kettle.
The Problem:
Scale acts as an insulator. If your heating element is covered in scale, it takes much more energy to heat the water. Furthermore, flakes of scale can break off and clog the tiny valves and “gicleur” holes inside the machine, leading to pressure loss.
The Solution:
Descaling involves running an acidic solution (like citric or tartaric acid) through the boiler. The acid reacts with the calcium carbonate, turning it into a soluble salt that can be flushed away. - Warning: Never descale a commercial machine yourself without training! If not done correctly, you can shift large pieces of scale that will permanently block the machine’s internal pipes.
Article 223: Understanding “Flavor Fatigue”
(Category: Sensory Skills | Word Count: ~210)
If you taste 20 different coffees in a row, you will experience Flavor Fatigue. Your taste buds and olfactory sensors become “saturated,” and everything starts to taste the same—acidic and bitter.
How to avoid it: - Rinse your mouth: Drink plenty of room-temperature water between samples.
- Cleanse the palate: Some cuppers eat a plain cracker or a slice of green apple to “reset” their tongue.
- Smell your own skin: This sounds strange, but smelling the scent-neutral skin on the back of your hand can help “reset” your nose from the intense aromatics of the coffee.
- Spit, don’t swallow: Professional tasters always spit out the coffee during a cupping session to avoid a “caffeine crash” and stomach irritation.
Article 224: The “Dead Space” in Grinders
(Category: Barista Skills | Word Count: ~230)
“Dead Space” is the physical volume inside a grinder between the burrs and the exit point. This is different from retention, as this coffee never leaves the machine unless it is manually cleaned out.
The Impact on Quality:
Coffee trapped in the dead space sits there for days, slowly oxidizing. If you haven’t used your grinder since yesterday, the first shot you pull will contain “dead” coffee that has lost all its sweetness and clarity.
The Barista’s Habit:
This is why the morning purge is so important. You must grind out and discard approximately 15\text{g} – 20\text{g} of coffee first thing in the morning. This ensures that the coffee you serve to your first customer is 100\% fresh and wasn’t sitting in the “dead space” overnight.
Article 225: Introduction to “Batch Brewing”
(Category: Brewing Methods | Word Count: ~290)
For a long time, “Filter Coffee” was seen as inferior to Espresso. This has changed with the rise of Precision Batch Brewers (like the Fetco or Moccamaster).
The Difference:
Unlike a standard home coffee maker, a professional batch brewer allows the barista to program: - Pre-infusion time: Soaking the grounds before the main brew.
- Pulse pouring: Mimicking a hand-pour to keep the temperature stable.
- Water temperature: Accurate to within 0.5^\circ\text{C}.
Why it’s great for Kenya:
Kenyan coffee is often very complex. Brewing it as a large batch (e.g., 2\text{ Liters} at a time) creates a very stable thermal environment, which can often extract more sweetness than a single-cup V60. For a busy café, it allows you to serve high-quality specialty coffee to a large number of people quickly and consistently.
Article 226: The “Third Wave” Water Recipe
(Category: Coffee Science | Word Count: ~250)
As we’ve learned, water is 98\% of your cup. Some baristas go as far as making their own water from scratch. This is often called “Remineralized Water.”
The Recipe:
You start with Distilled or Reverse Osmosis (RO) water, which has zero minerals. Then, you add specific amounts of: - Magnesium Sulfate (Epsom Salts): To “grab” the fruity and floral flavors.
- Sodium Bicarbonate (Baking Soda): To provide “alkalinity” and buffer the harsh acids.
By controlling the water exactly, a roaster in Nairobi can ensure their coffee tastes exactly the same when brewed in London or Tokyo. It removes the “variable” of local tap water quality.
Article 227: Why “Dark Roasts” Lack Origin Character
(Category: Roasting Knowledge | Word Count: ~220)
When you roast coffee dark (beyond the “Second Crack”), the chemical reactions are so intense that they destroy the Organic Acids and Volatile Aromatics that make a coffee unique.
At this stage, the sugars have carbonized (turned to ash) and the oils have oxidized. Whether the bean came from Nyeri, Kenya or Minas Gerais, Brazil, a dark-roasted bean will simply taste like “roast”—bitter, smoky, and charred. This is why specialty roasters almost always stick to Light or Medium roasts for Kenyan coffee; they want you to taste the farm, not the fire.
Article 228: The “Puck Screen” vs. “Shower Screen”
(Category: Barista Skills | Word Count: ~240)
We’ve discussed the shower screen (the part of the machine). Recently, many baristas have started using a Puck Screen (a loose metal mesh disc) on top of the coffee.
The Benefits: - Cleaner Machine: The puck screen prevents coffee grounds from being sucked back into the machine’s internal valves.
- Softer Water Entry: It acts as a secondary disperser, ensuring the water hits the coffee bed with zero “jets,” which further reduces channeling.
The Downside:
It is one more thing to clean! If you don’t soak your puck screens in detergent daily, they will build up old oils and start to make your fresh coffee taste stale. It’s a tool for the perfectionist who is willing to do the extra cleaning work.
Article 229: Understanding “Total Dissolved Solids” (TDS)
(Category: Coffee Science | Word Count: ~200)
TDS is the measurement of the concentration of your coffee. If you have a TDS of 1.35\%, it means that 1.35\% of your drink is dissolved coffee and 98.65\% is water.
We measure this using a Refractometer, which uses light to see how “dense” the liquid is. - Low TDS (e.g., 1.1\%): The coffee will taste watery, thin, and weak.
- High TDS (e.g., 1.6\%): The coffee will taste heavy, muddy, and overpowering.
The “Golden Rule” for filter coffee is usually between 1.2\% \text{ and } 1.5\%. Mastering TDS allows a barista to move from “guessing” if a coffee is good to “knowing” it is technically perfect.
Article 230: The Role of the “Q-Grader”
(Category: Coffee Education | Word Count: ~300)
A Q-Grader is the “Sommelier” of the coffee world. To become one, a person must pass 19 grueling exams administered by the Coffee Quality Institute (CQI).
What they do:
Q-Graders are licensed to score Arabica coffee using the international SCA Cupping Protocol. - They evaluate fragrance, flavor, aftertaste, acidity, body, balance, and “uniformity.”
- If they give a coffee a score of 80 points or higher, it is officially “Specialty Grade.”
In Kenya, Q-Graders work at the Nairobi Coffee Exchange, for exporters, and at high-end roasteries. They are the gatekeepers of quality. When you see a “Cup Score” on a bag of coffee (e.g., “Score: 87.5”), that number was given by a Q-Grader. It is a guarantee that the coffee is world-class.