Welcome to the Sunday ChemistryViews Quiz!

We explore a chemistry topic in this fun and short quiz which will be out in irregular intervals on a Sunday morning. Test your knowledge and learn something new in just a few minutes.

Ready to dive in? Let’s go!

The perfect milk foam in a cappuccino requires only air and heat—true or false? 🤔

See answer

❌ False!

Air and heat help, but without properly structured milk proteins, stable foam cannot form.

☁️ How Foam Forms

• Foam = Air in Milk — Whisking injects air, creating a dispersion of gas bubbles.

• Don’t Stir, Fold — Whisk by gently folding air in.

🧶 The Role of Proteins

• From Globules to Networks — Whey proteins (notably β-lactoglobulin and α-lactalbumin) are tightly coiled in their native state—like tiny wool balls.

• Unfolding via Shear — Mechanical energy unfolds these amphiphilic proteins, exposing hydrophobic sites that adsorb at the air–water interface and stabilize bubbles.

• Protein Content Matters — Cow’s milk, rich in proteins, foams reliably. In contrast, almond and rice milk contain less protein, making it harder to create stable foams.

• Fat: A Foaming Foe — Milk fat (especially lipolysis products like free fatty acids) disrupts protein networks and reduces foam stability.

🔥 The Importance of Temperature

• Heat Helps—But Carefully — Moderate heating (60–65ºC) enhances molecular motion, increasing protein flexibility. Beyond ~70°C, proteins denature irreversibly destroying the protein.

😈 Gravity: Foam’s Natural Enemy

• Drainage and Rupture — Liquid drains from bubbles under gravity, thinning them until they burst.

• Viscosity Slows Collapse — Cream (higher fat and protein content) resists collapse longer than low-viscosity systems like beer foam.

🔬 Component Effects

• Lactose — Increases viscosity and hinders protein diffusion, reducing foamability, but improves stability by retaining liquid and preventing bubble coalescence.

• Casein — Surface-inactive protein, increases viscosity and stabilizes foam indirectly by resisting drainage.

👅 Sensory Bonus

• Foam Enhances Flavor — Foam moves smoothly across the tongue toward the back of the mouth, enhancing aroma release as the liquid spreads more evenly over the taste buds.

🍳 Related Phenomena

• Same Principle in Meringue — Egg white proteins (especially ovalbumin) denature and form elastic films around air bubbles during whipping, using the same protein-interface dynamics as milk foam.