"Impact of (Very) High Gravity Fermentations on the Characteristics of Distilled Spirits and Carbon Footprints."
Understanding and controlling fermentation kinetics is critical for improving alcohol yield and consistency in spirit production. Under Very High Gravity (VHG) fermentations (>1.074 OG), full optimisation of the process under these stress conditions often requires extensive lab trials. This study presents a dual approach, combining predictive modelling with experimental optimisation to enhance fermentation outcomes and reduce wet-lab experimental work.
An artificial neural network (ANN) was developed to model fermentation kinetics using time-series data of cumulative CO₂ evolution. The model was trained on six original gravities under a set temperature curve and pitching rate, using a commercial active dried yeast (ADY) strain of Saccharomyces cerevisiae. A smoothed curve was generated by the trained ANN to extrapolate kinetic information and resulting in a predictive model with high accuracy (R² = 0.999) for unseen fermentations. From this format, the ANN was then optimised to predict the fermentation curves of “unseen” gravities.
In parallel, a Design of Experiments (DoE) framework was used to investigate the impact of yeast rehydration conditions on final ABV%. Variable osmotic pressures were applied to ADY via rehydration media at set temperatures, using two commercial S. cerevisiae strains and three pitching rates. The model explored the hypothesis that osmotic shock during rehydration could restore oxygen consumption capacity, improving stress tolerance. The resulting predictive model (RMSE = 0.256, R² = 0.96, p < .0001) enabled simultaneous testing of multiple variables, identifying pitching rate and yeast strain, as well as original gravity with rehydration media, as the most influential paired factors for ABV% optimisation under VHG conditions.
While linked in design, the independent results demonstrate the potential of integrating machine learning and statistical modelling with targeted experimental design. The talk will present the ANN architecture and kinetic modelling approach alongside DoE results, as well as the future potential for creating a stacked model, offering opportunities for early-phase optimisation and reduced experimental waste in VHG fermentation systems.