Why is 70°C advised as the maximum temperature for heating milk?

Heating milk beyond 70°C leads to the denaturation of proteins, particularly whey proteins. This process causes the proteins to unfold and interact in ways that can create off-flavors and undesirable aromas, negatively impacting the quality of the milk. When milk is heated too much, it can develop a cooked or scorched taste, which is generally not accepted in the context of foamed milk or beverages where the flavor profile is crucial. Maintaining the temperature below this threshold helps preserve the fresh flavor and overall quality of the milk, which is particularly important for baristas aiming to create excellent espresso drinks.

While improving foam quality, preventing bacterial growth, and enhancing sweetness are important considerations in milk preparation, they are not the primary reason for keeping the temperature at or below 70°C. The preservation of taste and quality through controlled heating is the core of this guideline.