Advantages of Modern Process Control and Fed-batch Fermentations in Enology
Mr. Charles Frohman, Ph.D. Candidate, Department of Food Science and Technology, NY State
Agricultural Experiment Station, Cornell University
ABSTRACT
In recent years, a number of analytical devices have been introduced which allow winemakers to monitor
the progress of alcoholic fermentations. Combined with cooling systems, these technologies can be used
to automatically control fermentation rates. Most currently available systems are based on CO2 mass
flow, must density, or osmotic pressure measurements. Theoretically, these systems would allow the
determination of sugar concentrations based on initial Brix values and fermentation progress. However,
differences in yeast growth, transformation efficiency, and by-product formation render this impracticable.
We present a system based on FT-NIR spectroscopy combined with chemometric methods that provides
accurate real-time information about key-fermentation parameters including glucose, fructose, and
ethanol concentrations throughout fermentations. Besides allowing precise control of fermentation rates,
real-time knowledge of sugar concentrations also permits winemakers to stop traditional batch
fermentations automatically at given residual sugar levels. More significantly, integrated process control
with in-line sugar analysis enables innovative fermentation strategies that include carrying out fed-batch
fermentations in enology. For example, a small partial amount of must may be initially fermented until a
certain target sugar concentration is reached. Then, the sugar concentration is kept constant by pumping
fresh must into the fermentation vessel throughout the fermentation. This approach is particularly
interesting for the fermentation of high gravity musts (hot climates, late harvest, and Icewines), which may
normally lead to hyperosmotic stress in yeast causing high acetic acid levels and, possibly, fermentation
problems. To demonstrate the opportunities of this application, the traditional batch fermentation of a
must initially containing 340 g/l of sugars was compared with a fed-batch approach, where a pump
delivered the same must at suitable rates to maintain sugar levels at 50 g/l. The fed-batch approach
showed constant fermentation rates and a reduction of final acetic acid levels from 1 to <0.2 g/l compared
with the traditional batch fermentation. Calibrated for other substrates, this system can be used in other
food and non-food fermentations, too.
BIOGRAPHY
Charles Frohman is a Ph.D. Candidate in the Department of Food Science at Cornell University. He
received a Bachelor of Science in Chemistry from Brown University in 2009. His current research studies
the effects of fed-batch vinifications with Saccharomyces cerevisiae - where very high gravity must is fed
continuously to a low gravity grape must fermentation - on fermentation kinetics, ethanol yields, yeast
viability, cooling requirements, and by-product formation. The objective of the project is to reduce energy
(cooling) requirements in winemaking and to modify yeast metabolic transformations in such a way as to
obtain wine containing lower concentrations of compounds with negative sensory attributes, such as
acetic acid.