The Chemistry of the Burn: High-Temperature Extraction and the Art of Steam Brewing

In the world of specialty coffee, 93°C (200°F) is the holy grail. It is the temperature where flavor compounds dissolve optimally without breaking down into bitter constituents.
The Ihomekee CM6810, being a steam-driven machine, breaks this rule. To generate 3.5 bars of steam pressure, the water in the boiler must reach 138°C (280°F). While it cools slightly as it travels to the coffee, it strikes the grounds at temperatures well above boiling.

This creates a unique chemical environment. It is High-Temperature Extraction. This article explores the food chemistry of scorching, the necessity of coarse grinding, and why the “Plastic Smell” reported by users might actually be a matter of thermal stress.

The Chemistry of Scorching: Hydrolysis and Pyrolysis

When water hits coffee above 100°C, it becomes an aggressive solvent.
1. Over-Extraction: High energy pulls out not just the oils and sugars, but the Tannins and Cellulose fibers. This leads to a woody, astringent taste.
2. Volatile Loss: Delicate aromatic compounds (esters, aldehydes) flash-evaporate instantly, leaving behind heavier, burnt notes.
This explains the “Strong” flavor profile. It is a chemically heavy cup, lacking the brightness of pump espresso but possessing a deep, dark intensity that pairs well with milk.

The Grind Size Equation: Why “Medium-Coarse”?

The manual explicitly warns: “Please use medium-coarse coffee ground.”
In a 9-bar pump machine, you use fine powder to create resistance.
In a 3.5-bar steam machine, resistance is dangerous. * Darcy’s Law: Flow rate is proportional to pressure difference and permeability.
If you use fine powder in the CM6810:
1. Choking: The 3.5 bars cannot push through the dense puck.
2. Pressure Spike: The boiler pressure rises until the safety valve pops.
3. Channeling: Or, the superheated steam blasts a hole through the puck, ruining the shot.
Using Medium-Coarse grind increases permeability. It allows the lower pressure steam to flow through, preventing the machine from becoming a pipe bomb and ensuring an even, albeit fast, extraction.

The “Plastic Smell”: Thermal Off-Gassing

User reviews frequently mention a “plastic smell.” * Thermal Stress: The ABS plastic housing surrounds a metal boiler reaching 140°C. If the insulation is imperfect, the plastic heats up. While food-safe, heated polymers can release Volatile Organic Compounds (VOCs) initially (off-gassing). * The Break-in Period: This usually dissipates after several heat cycles (“flushing the system”). It is a side effect of high-temperature components in a consumer-grade chassis.

Steam Wand Physics: Wet vs. Dry Steam

The CM6810 features a steam wand. Unlike commercial boilers that separate steam and water, this machine uses the same boiler water for steam. * Wet Steam: As the water level drops, the steam becomes “wetter” (more water droplets). * Dilution: This wet steam heats milk quickly but also dilutes it with water. It creates large, bubbly foam (macrofoam) rather than silky microfoam. It is perfect for a 1980s style Cappuccino, but difficult for Latte Art.

Conclusion: Mastering the Beast

The Ihomekee CM6810 is an instrument of brute thermal force. It does not finesse the coffee; it extracts it with the power of phase change.
To master it, the user must understand the chemistry of the burn. By using coarser grinds to manage flow and adding milk to balance the intense, high-temp extraction, one can craft a beverage that, while not “espresso” in the modern sense, is a deeply satisfying, caffeinated tradition.