Describe the chemical mechanisms of 'Angel's Share' during spirit maturation.

The 'Angel's Share' refers to the loss of spirit volume during maturation in wooden barrels. This loss occurs due to evaporation through the porous wood of the barrel. The chemical mechanisms driving this evaporation involve the diffusion of volatile compounds from the spirit into the surrounding environment. Ethanol, being a relatively small and volatile molecule, is a primary component of the Angel's Share. It diffuses through the wood at a rate influenced by temperature, humidity, and the specific characteristics of the barrel. Water also evaporates, though often at a different rate than ethanol, affecting the final alcohol concentration of the spirit. The evaporation process is not uniform across all compounds. Smaller, more volatile molecules tend to evaporate more readily than larger, less volatile ones. This means that the Angel's Share also involves the loss of other volatile flavor compounds, such as esters and aldehydes, though often in smaller proportions than ethanol and water. The rate of evaporation is influenced by environmental factors. Higher temperatures increase the rate of evaporation, while higher humidity levels can decrease it by reducing the concentration gradient between the spirit and the surrounding air. The type of wood used for the barrel also plays a role. Oak, with its characteristic porosity, allows for a controlled rate of evaporation, contributing to the unique flavor development during maturation. The char level of the barrel can affect this, as it changes the surface area and characteristics of the wood exposed to the spirit. Therefore, the Angel's Share is a complex process involving the selective evaporation of volatile compounds, influenced by environmental conditions and the properties of the barrel, ultimately contributing to the changing composition and flavor profile of the maturing spirit.