How to Calculate Alcohol Distillation Yield
Distillery yields are often measured using what’s referred to as a “Potent Spirit Yield”, measured in terms of litres of 100% (200 proof) alcohol produced per ton of malted barley used. This figure has remained fairly constant over the years regardless of changes to barley varieties and malting techniques used, and thus provides an effective benchmark.
The PSY figure is calculated based on an empirical equation which correlates the fermentable extract of malted barley with anticipated spirit yield in distilleries. Since its discovery in 1976, many experiments have been performed and this allows for accurate and repeatable calculations.
Batch distillation occurs by heating an ideal mixture of two volatile substances A and B to their boiling points until they vaporise, creating an enriched mixture enriched in component A as per Raoult’s law; its ratio will remain the same until further heat is applied; then this enriched vapor is directed through a condenser before being separated from its liquid source.
As part of this process, some components may be air sensitive and the connection with the atmosphere should either remain open through leaving an opening in the distillation apparatus, or better results are obtained when vacuum conditions are maintained using either a cow adaptor or (for particularly air sensitive compounds) Perkin Triangle apparatus. By keeping an opening open however, pressures of both liquid and vapor will have time to equalize, which helps protect equipment against damage.
