Hard-shell Fermentation Dynamics
August 30, 2019
I’ve discussed Miller, OIberholster, and Block’s work, as well as the differences between fermenting wine in concrete rather than stainless steel, in the past, but I wanted readers to know that a new paper has been published in the latest issue of the Australian Journal of Grape and Wine Research. Miller’s work has been on developing and refining a predictive mathematical model for wine fermentations. Predicative models are useful because, if they’re accurate, then they can let one know in advance the results for any given set of initial and fermentation condition. More importantly, to my mind an accurate predictive model is a demonstration that one actually knows what is happening. This specific paper looks at fermentation in concrete eggs.
Probably the most significant finding is that concrete eggs act more like an insulator than a heat sink.
Links to the paper are listed below.
Background and Aims: Concrete egg fermenters are of increasing interest to winemakers interested in expanding the range of sensory properties that emerge during fermentation. Winemakers and concrete egg fermenter vendors have made prior assumptions about the liquid mixing efficacy and heat transfer in egg fermenters, which have not been explored in the literature. These assumptions were therefore examined using a computational fluid dynamics approach, along with a model for fermentation dynamics, to compare a concrete egg fermenter with a jacketed cylindrical tank typically used for winemaking.
Methods and Results: The liquid temperature, external concrete surface temperature and sugar concentration in a concrete egg fermenter were monitored, and compared with values predicted from a reactor engineering model designed to simulate the fermentation dynamics of a concrete egg fermenter, to good agreement. Simulated mixing and temperature control were then compared in concrete eggs and cylindrical tanks. Finally, the impact of wall thickness and air velocity on fermentation dynamics was explored, with both variables found to have a significant impact on fermentation temperature and kinetics.
Conclusions: Superior mixing and temperature control was predicted in the jacketed cylindrical tank with the concrete shell found to function more as an insulator than a heat sink during fermentation.
Significance of the Study: This work represents the first quantitative exploration of concrete egg fermenters, and in doing so will act as a tool for winemakers interested in using concrete eggs as part of their winemaking practices.