Final answer:
When steaming milk has large bubbles and lacks shine, it is over-aerated, which results in a foamy and airy texture instead of being smooth and silky. Option A is correct.
Step-by-step explanation:
When steaming milk, if the milk has large bubbles and lacks shine, your milk is over-aerated. Properly steamed milk should have a velvety texture with fine, consistent microfoam and a glossy appearance. Large bubbles indicate that too much air has been incorporated into the milk during the aeration phase, which typically happens when the steam wand is too high in the pitcher or the steaming process is too aggressive.
To fix this, ensure the wand is just below the surface of the milk and introduce air gently. Over-aeration makes the milk foamy and airy rather than smooth and silky, which is essential for creating latte art and delivering a pleasant mouthfeel with your coffee.