Part 1: Coffee Chemistry & Physiology
Article 1: The Molecular Makeup of the Green Bean
The Kenyan green bean is a biological marvel, largely defined by the volcanic soils of the Rift Valley and the high-altitude climates of regions like Nyeri and Kiambu. At the molecular level, a green coffee bean is a dense matrix of cellulose containing roughly 1,000 different chemical compounds. The most critical for the Kenyan profile are the carbohydrates, which make up about 50% of the bean’s dry weight. While many assume “sugar” means sweetness, most of these are complex polysaccharides that contribute to the “body” and “mouthfeel” after roasting.
The defining characteristic of Kenyan Arabica (specifically varieties like SL-28 and Batian) is the high concentration of Phosphoric Acid. Unlike citric or malic acids derived from fruit, phosphoric acid is inorganic, absorbed from the mineral-rich volcanic soil. This creates the “sparkling” or “effervescent” sensation on the tongue that is prized globally. Additionally, the nitrogenous compound Trigonelline plays a dual role: it contributes to the development of aromatic compounds (pyridines) during roasting and provides the subtle bitterness that balances the high acidity.
Lipids, or coffee oils, comprise about 15% of the bean. In Kenyan coffees, these oils are exceptionally stable due to the slow maturation of the cherry at high altitudes. This stability ensures that the coffee maintains its freshness and “vibrancy” longer than beans grown in warmer, lower elevations. Understanding this molecular baseline is the first step for any student; you cannot roast or brew effectively without knowing the raw materials provided by the Kenyan farmer.
Article 2: The Physiology of Taste and Olfaction
To be a professional taster in the Kenyan industry, one must understand that “flavor” is a multisensory construct. Taste occurs on the tongue through gustatory cells, identifying the five basics: sweet, sour, salty, bitter, and umami. However, the “notes” we describe—such as blackcurrant, tomato, or hibiscus—are actually aromas detected by the olfactory bulb.
A critical concept for the student is Retronasal Olfaction. This is the process of aromas traveling from the back of the mouth up to the nasal cavity while swallowing or “slurping” coffee. In Kenyan coffee cupping, the forceful slurp is not just tradition; it aerosolizes the liquid, ensuring that the volatile organic compounds (VOCs) reach the olfactory receptors.
Students must also understand “sensory thresholds.” Every individual has a different sensitivity to bitterness or acidity. Training involves narrowing these gaps through “calibration.” For example, a student might struggle to find the “sweetness” in a high-acid SL-28 because the acidity “shouts” louder than the sugars. By understanding the physiology of how the brain prioritizes signals, a cupper can learn to look “behind” the acidity to find the complex sucrose layers underneath. This biological awareness prevents subjective bias and allows for objective quality analysis.
Article 3: Water Chemistry in Extraction
Water is the solvent that reveals the chemistry of the bean. For Kenyan coffee, which is celebrated for its delicate and complex acidity, water chemistry is a “make or break” factor. The two most important variables are Total Dissolved Solids (TDS) and Alkalinity.
In many parts of Kenya, groundwater can be “hard,” containing high levels of Calcium (Ca^{2+}) and Magnesium (Mg^{2+}). These minerals act like “magnets” that pull flavors out of the coffee grounds. Magnesium is particularly efficient at extracting sharp, fruity flavors, while Calcium tends to highlight heavier, creamier notes. However, if the water is too hard, it can lead to over-extraction, making the coffee taste chalky or bitter.
Even more critical is Alkalinity (not to be confused with pH). Alkalinity acts as a “buffer.” If your water has high alkalinity, it will neutralize the very acids that make Kenyan coffee famous. A Nyeri coffee brewed with high-alkalinity water will taste flat, earthy, and dull, losing its signature citrus “snap.” The ideal water for Kenyan coffee should have a total hardness of around 70–120 ppm and an alkalinity of around 40 ppm. Students will learn to use titration kits to test water and understand how to use filtration systems (like Reverse Osmosis with remineralization) to ensure the water profile matches the SCA (Specialty Coffee Association) standards.
Article 4: Chemical Changes During Roasting
Roasting is a controlled chemical breakdown. It begins with the Endothermic Phase, where the bean absorbs heat and the remaining 10–12% moisture begins to evaporate. The most significant chemical milestone is the Maillard Reaction, which usually begins around 150°C. This is a reaction between amino acids and reducing sugars that creates hundreds of color and flavor compounds known as melanoidins.
In Kenyan beans, which are high in amino acids, the Maillard phase must be managed carefully. If this phase is too fast, the coffee will lack complexity; if too slow, the coffee may taste “baked” or bready. Following Maillard is Caramelization, the thermal decomposition of sucrose. This occurs at higher temperatures (around 170–190°C) and is responsible for the caramel, chocolate, and dark fruit notes.
Finally, we track the degradation of Chlorogenic Acids (CGA). As the roast progresses, CGAs break down into quinic and caffeic acids. If a Kenyan roast is pushed too dark, the high initial CGA content can result in an unpleasantly metallic or “burnt medicine” taste. Students will learn that for Kenyan coffee, the goal of roasting chemistry is “preservation”—applying enough heat to develop sugars while stopping before the unique organic acids are destroyed.
Part 2: Sensory Analysis Foundations
Article 5: The SCA Flavor Wheel & Sensory Lexicon
The SCA Flavor Wheel is the “dictionary” of the coffee world. For the Kenyan student, this tool is essential for communicating with international buyers in Europe, America, and Asia. The wheel is organized from the center outward; you start with general categories (Fruit, Floral, Sweet) and move to specific descriptors (Blackberry, Jasmine, Brown Sugar).
In this module, students practice using the WCR (World Coffee Research) Sensory Lexicon. This is a set of objective references. For example, if we say a coffee has a “citrus” note, the lexicon specifies whether it is “lemon” or “orange” based on specific chemical standards. In the context of Kenya, we spend extra time on the “Fruity” and “Floral” sections.
Students will practice “triangulation” of flavors. Why does a Ruiru 11 taste different from an SL-28? Often, the Ruiru 11 has a more “savory” or “earthy” undertone. By using the wheel, students learn to articulate these differences. We also introduce the concept of “negative” attributes on the wheel, such as “Papery” or “Musty,” which help identify issues in storage or processing.
Article 6: Identifying Sensory Defects
A Coffee Quality Analyst is, first and foremost, a gatekeeper. Identifying defects is more important than finding “notes of jasmine.” In this article, we cover the chemical origins of common defects found in the supply chain.
Phenol is a devastating defect that tastes like harsh chemicals or medicine; it is often linked to localized fermentation issues or water contamination. Over-fermentation (stinkers) occurs when cherries are left in the fermentation tank for too long, leading to a rotten, vinegary, or “compost” flavor. This is a risk in Kenyan “double-washed” processing if the second soak is not monitored.
We also study the Potato Defect, caused by a specific bacteria entering the cherry through a stink bug puncture. While more common in Rwanda and Burundi, it occasionally appears in Kenyan lots. It produces an unmistakable smell of raw, peeled potato. Students are trained to detect these defects in the “dry fragrance” (before adding water) and the “wet aroma.” Identifying a single “stinker” bean in a sample of 300g is a skill that saves exporters thousands of dollars.
Article 7: Acid Profiling and Intensity
In the Kenyan market, “Acidity” is a positive attribute, often called “brightness.” However, not all acidity is created equal. This article teaches students to categorize acids into four main types found in coffee: Citric, Malic, Tartaric, and Phosphoric.
- Citric Acid: Common in Nyeri coffees; tastes like lemon or lime.
- Malic Acid: Common in Kirinyaga coffees; tastes like green apple or pear.
- Tartaric Acid: Found in some “natural” processed Kenyans; tastes like grapes or wine.
- Phosphoric Acid: The “hidden” gem of Kenya; it feels like the tingle of a carbonated drink.
Students perform a “Spiked Water” exercise, where pure organic acids are added to water at varying concentrations. This “muscle memory” for the tongue allows a cupper to say, “This coffee has high citric intensity but low malic sweetness.” We also discuss the “Quality of Acidity.” Is it “ripe” (like a sweet orange) or “unripe” (like a sour lemon)? In Kenya, the most expensive coffees are those where the acidity is “structured”—meaning it is intense but balanced by high sugar content.
Article 8: Mouthfeel and Body Dynamics
“Body” is the tactile sensation of the liquid in the mouth—its weight and texture. It is not a “flavor” but a “feeling.” In Kenyan coffee, body is often described along a spectrum from “Tea-like” to “Syrupy.”
The body is created by non-soluble solids and oils suspended in the brew. During this module, students learn to evaluate Texture (smooth, silken, gritty, or astringent) and Weight (thin/watery vs. heavy/creamy). We use “reference liquids” like whole milk, skim milk, and water to calibrate the tongue’s sense of weight.
A critical lesson here is the difference between “Body” and “Astringency.” Astringency is a drying, puckering sensation (like over-steeped tea) that is usually a result of poor roasting or under-ripe picking. A “good” Kenyan body should be “clean”—it should disappear from the palate without leaving a dry or sandy feeling. For espresso cupping, this becomes even more vital, as the concentration amplifies both the positive creamy textures and the negative gritty ones.
Part 3: The Art and Science of Roasting
Article 9: Thermodynamics and Heat Transfer
Roasting is the physics of energy transfer. Inside a drum roaster, three types of heat are at work. Conduction is the direct contact between the hot metal drum and the bean. Convection is the movement of hot air through the beans. Radiation is the heat emitted from the drum walls and the burner itself.
Kenyan beans are typically very dense because they are grown at 1,500+ meters above sea level. Dense beans have a “tight” cellular structure, which means they conduct heat more slowly to their center but can also “hold” more heat once they get hot. A common mistake when roasting Kenyan coffee is using too much initial heat (Conduction), which “scorches” the outside of the bean while the inside remains raw and “grassy.”
Students learn to balance the “Airflow” (Convection) to ensure the heat penetrates the center of the bean. We discuss the “Thermal Mass”—how the weight of the coffee batch affects the temperature of the roaster. For a 5kg batch of Kenyan AA, the roaster must “charge” (start) at a specific temperature to ensure the beans have enough energy to carry through to the end of the roast.
Article 10: Roast Profiling and the Rate of Rise (RoR)
The “Profile” is the story of the roast. Modern roasters use software to track the Rate of Rise (RoR), which is the number of degrees the coffee increases per minute (or per 30 seconds). The golden rule for specialty Kenyan coffee is a constantly declining RoR.
If the RoR “flicks” upward at the end of the roast, the sugars can burn, turning the sweet Kenyan berry flavor into a bitter “charcoal” taste. If the RoR “crashes” (drops too fast), the coffee becomes “baked,” losing its acidity and tasting like flat bread or paper. Students practice “marking” milestones: the Turning Point (when the beans start to heat up), the Yellowing Phase, and First Crack. For Kenyan beans, “First Crack” is a violent, loud event because of the bean’s density. Managing the energy after First Crack is where the best roasters are made; this is the “Development Time” that determines if the coffee will be a light-citrus filter roast or a medium-berry espresso roast.
Article 11: The Stages of a Roast: Drying to Finish
We divide the roasting process into three distinct time-blocks. - The Drying Phase: From charge to about 150°C. Even though the beans look dry, they contain 10% water. This water must be evaporated evenly. In Kenyan coffee, rushing this phase can lead to uneven development.
- The Maillard Phase (Yellowing): From 150°C to the start of First Crack. This is where color changes from green to yellow to light brown. This is the “Flavor Construction” phase. Extending this phase slightly can increase the “Body” of a Kenyan coffee.
- The Development Phase: From the start of First Crack to the end of the roast. This is the most delicate stage. For Kenyan coffees, we typically aim for a Development Time Ratio (DTR) of 12% to 18%.
Students will perform “Roast Color” tests using an Agtron machine. An Agtron 65 (medium-light) is often the “sweet spot” for Kenyan AA, as it develops enough sugar to balance the phosphoric acidity without introducing “roasty” carbon notes.
Article 12: Roastery Management and Quality Control
A professional roaster in Kenya must also be a business manager. This article covers Inventory Management and Green Coffee Maintenance. Green coffee is “alive”; it respires. If stored in a humid environment in Mombasa, it will age rapidly and taste “baggy.” If stored in the dry air of Nairobi, it might lose too much moisture, making it difficult to roast.
We teach the “Sample Roasting” protocol. Before buying 50 bags from an estate, a roaster must roast a 100g sample. This sample roast is used to check for defects and determine the coffee’s potential. Students also learn about Degassing. Freshly roasted coffee is full of CO_2, which interferes with flavor extraction. For Kenyan coffees, which are very dense, they often “peak” in flavor 5 to 10 days after roasting. Students will create a “QC Calendar,” cupping their production roasts every day for a week to understand how their roast profile ages and when it should be delivered to the customer.
Part 4: Coffee Quality Analysis (CQA)
Article 13: Green Coffee Grading (The Kenya System)
The Kenyan grading system is world-famous but often misunderstood. It is primarily based on Screen Size. - AA: Screen size 17/18 (Large).
- AB: Screen size 15/16.
- PB: Peaberry (single round bean).
- C: Screen size 14/15 (Smaller).
- E: Elephant beans (two beans joined).
However, size does not always equal quality. An “AB” from a high-altitude farm in Murang’a can often outscore an “AA” from a lower-altitude estate. Students learn to use “Sizing Screens” to verify a lot’s grade. We also perform a Visual Defect Count. Following the SCA protocol, a 350g sample is inspected. We look for “Primary Defects” (Full Black, Full Sour, Fungus) and “Secondary Defects” (Broken beans, Insect damage). In the high-stakes Kenyan auction, a few black beans can drop a coffee from “Grade 1” to “Grade 3,” costing the farmer millions of shillings.
Article 14: Moisture and Density Measurement
In CQA, we move from the “subjective” (taste) to the “objective” (measurement). Every student will learn to use a Moisture Meter. The ideal range for green coffee is 10.0% to 12.0%. Above 12.5%, the coffee is at risk of “molding” and developing Ochratoxin A. Below 9%, the coffee has “died” and will taste like straw or hay.
Density measurement is equally important. We use the “Displacement Method” or a digital density meter. Kenyan coffees are among the densest in the world (700+ g/L). High density indicates that the coffee was grown slowly at high altitudes, allowing the plant to pack more nutrients into the seed. This density is why Kenyan coffee can withstand high roasting temperatures. Students will learn how to correlate density with altitude and variety, providing a “map” of the coffee’s quality before it ever reaches the cupping table.
Article 15: The Nairobi Coffee Exchange (NCE) Protocols
This module provides a deep dive into the “Heart of the Kenyan Coffee Trade.” The NCE is where most Kenyan coffee is sold via an auction system. Students learn about the “Catalogue,” which lists every lot for sale.
We discuss the role of the Liquorer. A liquorer is a specialized Kenyan cupper who evaluates hundreds of samples a day. Their score determines the “Reserve Price.” We teach students how to read an NCE “Report,” understanding terms like “Outturns” (a unique code for a specific factory’s weekly production). This article emphasizes the ethics of grading; a CQA professional must be impartial, ensuring that the farmer is paid fairly for the actual quality of their crop. We also explore the “Direct Sale” (Second Window) model, where farmers bypass the auction to sell directly to international roasters.
Article 16: Statistical Consistency in Quality Control
A single cup of coffee can be a fluke. Professional QC requires Statistical Significance. In this module, we teach “The Rule of Five.” When cupping a single lot, we always prepare five cups. If one cup tastes different, it indicates “Inconsistency” in the lot (likely a few bad cherries mixed in).
Students learn to calculate Standard Deviation in their scoring. If three cuppers score a coffee 85, 86, and 85, they are “Calibrated.” If they score 82, 88, and 84, there is a problem with the sensory panel. We introduce “Control Charts” to track the quality of a farm’s output over several months. This data-driven approach allows an exporter to guarantee to a buyer that every container shipped will meet the exact same flavor profile, which is the hallmark of a professional CQA operation.
Part 5: Advanced Cupping & Espresso Evaluation
Article 17: The SCA Cupping Protocol
The Cupping Table is the “Courtroom” of coffee. We follow strict SCA standards: - Ratio: 8.25g of coffee per 150ml of water.
- Grind: Slightly coarser than drip filter.
- Temperature: 93°C (200°F).
Students learn the “Ritual.” First, “Fragrance”—smelling the dry grounds. Then, “Aroma”—smelling the wet grounds after pouring. At 4 minutes, we “Break the Crust,” pushing the grounds down with a spoon and inhaling the steam. This is often where the most intense floral notes of Kenyan coffee are found. After skimming the foam, we wait until 10–12 minutes when the coffee is cool enough to slurp. We score on ten attributes: Fragrance/Aroma, Flavor, Aftertaste, Acidity, Body, Balance, Uniformity, Clean Cup, Sweetness, and Overall. A Kenyan coffee scoring above 80 is “Specialty,” above 85 is “Excellent,” and above 90 is “Presidential/Exemplary.”
Article 18: Calibration: Finding the “North Star”
Calibration is the most difficult sensory skill. It is the ability to put aside personal preference and use the “Global Standard.” In this module, students cup the same three coffees: a low-quality commercial blend, a standard Kenyan AB, and a “top-lot” Nyeri AA.
We discuss why “acidity” in a Kenyan coffee might be scored a 9.0 by a Kenyan cupper but only an 8.0 by a cupper who prefers the “mellow” profile of Brazilian coffees. Calibration sessions involve “Blind Cupping,” where the identities of the coffees are hidden. Students must justify their scores using the Sensory Lexicon. We also use “Reference Samples”—coffees that have been pre-scored by a panel of experts—to help students “reset” their palates. Calibration ensures that an “87-point” coffee in Nairobi is recognized as an “87-point” coffee in London or Tokyo.
Article 19: Espresso Cupping and Deconstruction
Espresso is the “Magnifying Glass” of coffee chemistry. Because it uses high pressure and a 1:2 ratio (instead of the cupping 1:18 ratio), every flavor is amplified ten times.
In “Espresso Cupping,” we don’t just drink a shot. We perform a Salami Shot extraction. We catch the first 10 seconds in one cup, the next 10 in another, and the final 10 in a third. - Cup 1 (The Head): Highly acidic, salty, and intense.
- Cup 2 (The Heart): Sweet, balanced, and syrupy.
- Cup 3 (The Tail): Bitter, watery, and thin.
Students learn to identify the “Sweet Spot” where these three elements balance. For Kenyan espresso, the challenge is managing the high acidity so it doesn’t taste “sour” or “salty.” We also practice “Diluted Espresso Cupping,” where we add hot water to a shot (making an Americano) to see if the coffee’s terroir (the Kenyan blackcurrant) survives the high-pressure extraction process.
Article 20: Dialing In: From Cupping Table to Bar
The final module is the synthesis of the entire curriculum. “Dialing in” is the process of adjusting brewing variables to achieve a specific sensory goal discovered on the cupping table.
If our CQA report says a coffee has “High Malic Acidity and Toffee Sweetness,” but the espresso machine is producing “Sharp Lemon and Ash,” the student must diagnose the problem. - Is it the Temperature? Lowering the temp might reduce bitterness.
- Is it the Grind? Making it finer increases extraction and sweetness.
- Is it the Yield? Pulling a longer shot (1:2.5) might help balance the intense Kenyan acids.
Students will create “Brew Recipes” for different Kenyan varieties. They will learn that an SL-28 requires a different approach than a Batian. The course concludes with a practical exam: students are given a “mystery” Kenyan coffee, must perform a green grading, roast it to a specific profile, cup it to assign a score, and finally, “dial it in” as a perfect espresso shot that represents the very best of Kenyan coffee heritage.