How do terracotta bottle chillers work?

Answer 1

They work by allowing water to evapourate at their surface. When water is in contact with air, the faster-moving, more energetic (ie hotter) molecules tend to fly away into the air, leaving the less energetic, cooler ones behind. So water exposed to air tends to cool down. Our sweat works the same way to cool us down.

Because the terracotta is porous, when water evapourates from the surface, more water is conveyed out by capillary action. I shan't bother to explain capillary action, it's in Wikipedia, and it's what causes sap to rise up inside trees.

Answer 2

Terracotta bottle chillers work by first soaking them in water and then placing them in the freezer. The terracotta material absorbs the water and retains it, helping to keep the bottle cool once it is placed inside. As the water evaporates, it carries away heat from the bottle, effectively cooling it down.