Fadtab

Fadtab denotes the total amount of liquid lost during aging in oak barrels. It consists primarily of two mechanisms: evaporation through the wood's pores and absorption/extraction in the wood (the chemistry by which the wood exchanges components with the spirit).

Mechanisms

• Evaporation (the angels' share): Evaporation occurs through the tree's microscopic pores. Ethanol evaporates more readily than water, and therefore the interpretation of the spirit's composition changes over time. Evaporation results in a volume loss and affects the concentration of flavor compounds in the whisky.
• Absorption and extraction: The wood absorbs part of the liquid and at the same time releases its compounds to the spirit. Precipitated compounds from the wood, such as vanillin and lignans, impart color and aroma. At the same time, the relative amounts of water and alcohol in the liquid change as something is absorbed by the wood and something is extracted.

Factors affecting barrel loss

• Climate and storage conditions: Temperature and humidity play a major role. Warm conditions increase evaporation and the rate of chemical changes; cooler conditions typically reduce the loss.
• Barrel type and previous contents: New oak (first-fill) often has a more pronounced extraction of color and aroma than used barrels (second-fill). The previous contents the barrel has housed also influence which compounds are exchanged.
• Fill level: The more the barrel is filled, the less surface contact with air there is, and thus lower annual barrel loss. Lower filling increases the contact surface and can increase evaporation.
• Age and condition of the barrel: Over time the wood becomes less dense and less prone to releasing compounds, which can alter the rates of both evaporation and extraction.
• Storage location and storage conditions: Factors such as floor surface, exposure to sunlight and the warehouse's ventilation can influence temperature cycles and thus the rate of barrel loss.

Impact on the whisky's development

• Color: The extraction of the wood's color compounds and the evaporation of water change the whisky's color over aging.
• Aroma and flavor: The wood's aroma- and flavor compounds (such as vanillin and lignans) are imparted to the spirit, creating spicy, sweet, and roasted notes. At the same time, certain volatile alcohols and water are reduced as evaporation occurs.
• Structure and body: Micro-oxidation of the spirit through the wood contributes to changes in ester and acid content, affecting balance, roundness, and mouthfeel.

Measurement and significance in aging

• Angels’ share: Barrel loss is often described as a portion of volume that disappears due to evaporation and absorption into the wood. The rate varies with climate, barrel type and fill level, but it is a central concept in assessing how much whisky remains and how the flavor develops.
• Practical significance: Barrel loss is not just a loss in volume; it is an active part of the whisky's development. When planning aging, producers take expected barrel loss into account in calculations of final yield, consistency, and flavor profile.