Final answer:
The correct temperature of the sugar syrup for making Italian meringue is 120°C (248°F), which corresponds to the soft-ball stage that is optimal for meringue stability.
Step-by-step explanation:
For Italian meringue, it's crucial to add the sugar syrup to the egg whites at a specific temperature to ensure they whip up properly and safely. The correct temperature to start whipping the egg whites while adding the hot sugar syrup is around 120°C (248°F).
At this temperature, the sugar syrup has reached the soft ball stage, meaning it has cooked to a point where it will form a soft, pliable ball when a small amount is dropped into cold water. This temperature is critical because it ensures that the egg whites will reach a safe temperature when the hot syrup is slowly poured into them, effectively pasteurizing the egg whites to eliminate any potential harmful bacteria.
Starting to whip the egg whites at this temperature allows for the gradual incorporation of the hot syrup, resulting in a stable and glossy meringue that's safe to use in various desserts like mousses, pies, or as a topping for cakes without any concerns about raw egg consumption.