The air, upon being heated, bursts through the peel of the apple, carrying the juice with it.
Why does an apple become soft when roasted?
Because the air in the cells of the apple expands, and breaks those cells, so that the apple becomes soft.
What part of the apple first becomes soft?
The outside, because it is first heated.
Why do all fruits and vegetables become soft when cooked?
Because the heat expands the air in them, and thus breaks up their cells, so that they become soft.
Why does wood make a snapping noise when burning?
Because the air in the cells of the wood bursts them apart, thus making the noise.
Why are sparks of fire thrown out?