Here is the seventh batch of 10 articles (Articles 61 through 70). This batch covers the technicalities of coffee freshness, the “bloom” phenomenon, and the specifics of Kenyan coffee grading.
Article 61: The Science of the “Bloom”
(Category: Brewing Methods | Word Count: ~260)
When you pour hot water over fresh coffee grounds, you’ll notice them swell and bubble. This is called the “bloom.” But what is actually happening?
During the roasting process, carbon dioxide (CO_2) is trapped inside the coffee beans. When you grind the beans and add hot water, the gas is rapidly released. If you don’t allow this gas to escape, it will repel the water, preventing it from penetrating the grounds and extracting the flavor.
The Technique:
Pour about twice the weight of the coffee in water (e.g., 30\text{g} of water for 15\text{g} of coffee). Gently stir or swirl to ensure every ground is wet. Wait for 30 to 45 seconds. Once the bubbling stops, you can proceed with the rest of your pour.
A good bloom is a sign of freshness. If your coffee doesn’t bubble or “grow” during this phase, it is likely stale and has already lost its aromatic gases.
Article 62: Kenyan Coffee Grading: What “AA” Really Means
(Category: Coffee Bean Knowledge | Word Count: ~310)
In Kenya, coffee is graded by size and shape before it is auctioned. Many people think “AA” refers to quality or taste, but it actually refers to the physical size of the bean.
The Main Grades:
- AA: These are the largest beans, screened at size 17 or 18 (7.22\text{ mm} or larger). They are highly prized because large beans often contain more oils and sugars and roast more evenly.
- AB: This is a combination of A (size 16) and B (size 15) beans. While smaller than AA, AB lots often possess incredible flavor profiles and are the backbone of many specialty roasts.
- PB (Peaberry): As discussed before, these are single, round beans from cherries that only developed one seed.
- C: Smaller beans than AB.
- TT & T: These are the smallest, lightest beans, often separated from the larger grades by air flow.
The Quality Factor: While “AA” is the premium size, a “C” grade coffee can sometimes taste better than an “AA” if the processing and terroir were superior. Always look for the cupping score alongside the grade!
Article 63: The 4 Ms of Espresso (Le Quattro M)
(Category: Barista Skills | Word Count: ~240)
In traditional Italian coffee culture, the perfect espresso depends on “The 4 Ms.” Mastering these four variables is the core of any barista’s training. - Macchina (The Machine): The espresso machine must be clean, well-maintained, and set to the correct pressure (9\text{ bars}) and temperature (90^\circ\text{C}-96^\circ\text{C}).
- Macinadosatore (The Grinder): The grinder must have sharp burrs and be adjusted (dialed in) to the correct particle size for that specific coffee.
- Miscela (The Blend): The quality of the coffee itself. It must be fresh, high-quality, and roasted correctly.
- Mano (The Hand): This is the skill of the barista. It includes dosing, distribution, tamping, and knowing when to stop the shot.
If any one of these “Ms” is missing or poor, the quality of the espresso will suffer. A great barista knows how to balance all four to achieve perfection.
Article 64: Why Dark Roasts Taste “Oily”
(Category: Roasting Knowledge | Word Count: ~220)
Have you ever noticed that dark-roasted beans look shiny and oily, while light-roasted beans look dull and dry? This is not something added to the coffee; it is the coffee’s internal chemistry.
Inside every coffee bean are lipids (oils). During a long or hot roast, the internal structure of the bean becomes more porous and brittle. Eventually, the heat causes the internal pressure to push these oils through the microscopic pores to the surface of the bean. - Light/Medium Roast: The cell structure remains intact, keeping the oils inside.
- Dark Roast: The “Second Crack” in roasting physically breaks the bean’s structure, causing the oils to coat the exterior.
While some people like the “roasty” flavor of these oils, they oxidize very quickly once they hit the air. This is why dark roasts tend to go stale much faster than light roasts.
Article 65: Understanding “Pre-infusion” vs. “Pulse Pouring”
(Category: Brewing Methods | Word Count: ~290)
In the world of pour-over coffee (like V60 or Chemex), your pouring style dictates the extraction. Two common techniques are Continuous Pouring and Pulse Pouring.
Continuous Pouring:
You pour water slowly and steadily to keep the water level in the filter constant. - Benefit: It maintains a very stable temperature in the coffee bed.
- Result: A very clean, consistent, and predictable extraction.
Pulse Pouring:
You pour a specific amount of water (e.g., 50\text{g}), wait for it to drain slightly, and then pour again. - Benefit: Each “pulse” creates turbulence, which agitates the coffee grounds and can increase extraction. It also allows you to extend the brew time.
- Result: Usually a heavier body and more intense sweetness, but with a higher risk of over-extraction if the grind is too fine.
Most modern baristas use a “Hybrid” approach: one long bloom (pulse), followed by two or three steady pulses to reach the final weight.
Article 66: The Danger of “Over-Tamping”
(Category: Barista Skills | Word Count: ~210)
A common myth among beginner baristas is that if the espresso is running too fast, you should just “tamp harder.”
The Reality:
Coffee grounds can only be compressed so much. Once you reach “maximum density,” pushing harder doesn’t do anything to the coffee—but it might hurt your wrist or shoulder. Most research shows that after about 15\text{kg} (33\text{lbs}) of pressure, the flow rate of the espresso doesn’t change.
The Solution:
If your espresso is too fast, do not tamp harder. Instead, you must adjust your grinder to a finer setting. Tamping is about creating a level and uniform surface, not about using brute force. Consistency in your tamp is far more important than the amount of weight you apply.
Article 67: Coffee “Taints” and “Defects” in Cupping
(Category: Sensory Skills | Word Count: ~330)
During a cupping session, baristas look for “defects”—unpleasant flavors caused by problems during harvesting, processing, or storage.
Common Defects: - Phenolic/Chemical: Tastes like medicine or iodine. Often caused by picking unripe cherries or water contamination.
- Ferment: A sour, rotting-fruit taste. This happens when coffee sits in fermentation tanks for too long or is not dried quickly enough.
- Musty/Moldy: Tastes like a damp basement. This occurs if the coffee was stored in a humid environment and developed mold.
- Potato Defect: Specific to East African coffees (though rare in Kenya), where a certain bacteria causes the coffee to smell and taste exactly like raw potatoes.
Recognizing these defects is vital for a Q-Grader or an exporter. If a single defective bean ends up in a sample, it can lower the score of an entire lot of coffee, potentially costing the farmer thousands of shillings in lost revenue.
Article 68: The “Basket” Matters: Precision Filter Baskets
(Category: Barista Skills | Word Count: ~240)
Not all portafilter baskets are created equal. Standard baskets that come with espresso machines often have inconsistent hole sizes and uneven spacing.
Precision Baskets (like VST or IMS):
Specialty cafes use precision-engineered baskets. These are manufactured with laser-cut holes that are exactly the same size and perfectly distributed across the bottom.
Why pay more for a basket? - Even Extraction: If one side of the basket has more holes than the other, water will rush to that side, causing channelling.
- Higher Extraction: Because the holes are more efficient, you can actually use a finer grind without clogging the basket, leading to a sweeter, more developed flavor.
- Consistency: You can move your “dial-in” from one group head to another with total confidence that the baskets will perform identically.
It is one of the cheapest upgrades a café can make to immediately improve the quality of their espresso.
Article 69: The “Roast Profile”: Following the Curve
(Category: Roasting Knowledge | Word Count: ~270)
Roasting isn’t just about the final color; it’s about how you got there. Roasters use software (like Artisan or Cropster) to track a “Roast Profile”—a graph showing the temperature of the beans over time.
Key Milestones on the Curve: - Turning Point: The moment after you drop cold beans into a hot drum when the temperature stops dropping and starts rising.
- Rate of Rise (RoR): How many degrees the temperature increases per minute. A steady, declining RoR is usually the goal for a balanced roast.
- Development Time Ratio (DTR): The percentage of the total roast time spent between the “First Crack” and the end of the roast. Typically, this is between 15\% and 25\%.
By following these profiles, roasters can ensure that the “Nyeri AA” they roast on Monday tastes exactly the same as the batch they roast on Friday.
Article 70: Why we “Purge” the Grinder between Changes
(Category: Barista Skills | Word Count: ~190)
When you adjust your grinder from “coarse” to “fine,” the change isn’t immediate. There is always a small amount of coffee—about 5\text{g} to 15\text{g}—trapped in the “chute” or the space between the burrs. This is called grinder retention.
If you make an adjustment and immediately pull a shot, that shot will be a mixture of the old grind setting and the new one. This will confuse you and make “dialing in” impossible.
The Rule:
Every time you move the grind adjustment collar, you must “purge” (grind and discard) a small amount of coffee to clear out the old setting. Only then can you accurately test the results of your change. Waste is a part of precision!
That brings us to 70 articles! 180 more to go.