Final answer:
Biscuits expand as a result of carbon dioxide gas produced by the fermentation of yeast in the dough, which causes the dough to rise when baked. Charles's Law explains the expansion of gas bubbles at higher temperatures, leading to the fluffy texture of baked biscuits.
Step-by-step explanation:
Biscuits expand when moisture from dough or the air penetrates them. Biscuits, like bread, get their fluffiness from a process similar to fermentation, where yeast metabolizes sugars. This fermentation process generates carbon dioxide gas, which is trapped within the dough. When the dough is cooked, this gas expands due to Charles's Law, which states that a gas will expand when the temperature increases. As a result, the dough becomes light and fluffy, resulting in soft, risen biscuits.
The small holes seen in biscuits are due to carbon dioxide bubbles formed during fermentation. It's the baking process involving high temperatures that causes these gas bubbles to expand, due to the properties of gases as described by Charles's Law, referenced in section 14.4. The characteristic texture of baked goods is a product of this expansion. When the item cools down, the air or moisture surrounding it can lead to further expansion of these holes, which is especially noticeable in items with a high ratio of moist ingredients or in humid environments.