Why the sweetness seems to rise
Warming does not create more sugar. It changes how strongly your senses register what is already there. Sweetness begins when sugar molecules activate receptors on the tongue; temperature can affect how those receptors respond, so a very cold bite may produce a weaker sweetness signal than a warmer one.
Temperature also changes the aroma reaching your nose. As ice cream softens, more of its aroma compounds can escape into the air. Smell contributes to flavor, so a fuller aroma can make the whole bite seem more intense—including its sweetness.
A recipe has a serving temperature
Ice cream is a mixture of ice crystals, fat, air, and a concentrated liquid portion. As it warms, some ice melts and the balance shifts: the texture becomes softer, and flavors spread more readily across the tongue. These changes happen alongside the sensory effects of temperature, making a softened scoop seem richer and sweeter even though no sugar has been added.
That is why the first bite straight from the freezer may taste restrained, while a later spoonful tastes more vivid. The dessert has not become sweeter in the literal sense; your mouth and nose are receiving a stronger impression of its sweetness.
