The reduction-oxidation potential, or redox potential, in a fermenting juice can influence the reactions both in the juice and those within the yeast cells during wine fermentations. The ability to monitor and control the redox potential at a chosen value by adding air during a red wine fermentation was demonstrated in triplicate at the 100L scale. The Brix curves and reduction-oxidation potential patterns in the controlled fermentations were compared to those in the un-aerated fermentations. The redox control system consisted of a commercial pH meter with a reduction-oxidation electrode and a custom-designed electronic controller. The study showed the reduction-oxidation potential could be controlled at 215 mV, well above its natural level throughout the fermentation. The reduction-oxidation potential control resulted in both faster peak fermentation rates and an earlier completion of the wine fermentations. The analysis of these fermentation curves by a mathematical model indicates that both yeast cell viability and the specific maintenance rate of the viable cells were significantly increased by controlling the redox potential during the fermentation.

Combined with real-time monitoring of density and temperature, the control of the redox potential provides a new approach to influencing cell metabolism during growth, cell viability and non-growing yeast activity in wine fermentations. Prior research indicates that the problem of sluggish and incomplete fermentation can be alleviated by maintaining a constant redox potential during the ethanol fermentation. A secondary trait of hydrogen sulfide formation from elemental sulfur also seems to be associated with the development of low redox potentials during fermentation and this might be prevented by the deliberate control of redox potentials in a certain range. While the control of the redox potential during wine fermentations has been demonstrated previously at the research scale (100 L), the ability to control it in larger volumes typically seen in commercial conditions remained unanswered. Wine fermentations from the same load of Cabernet Sauvignon grapes from the 2021 harvest were conducted at three volumes: 100 L and 1500 L in a research winery and 10,000 L in a commercial winery. Using only pulses of air delivery, the redox potential was successfully controlled to −40 mV referenced to a silver/silver chloride electrode throughout the fermentations, at all scales. This appears to be the first published result of a controlled fermentation trial that includes the commercial scale and demonstrates the scalability of control of redox potential in wine fermentations.

The kinetics of the autoxidation reaction of tartaric acid in an air-saturated solution in the presence of Fe(II) show autocatalytic behavior with distinct initiation, propagation, and termination phases. The initiation phase, which involves activation of dissolved oxygen, decreases with increasing pH, over the test range of pH of 2.5–4.5, indicating that activation of oxygen is catalyzed by an Fe(II)–tartrate complex. The autocatalytic nature of this reaction indicates the presence of a catalytic intermediate that is produced during the initiation phase and regenerated during the propagation phase. The addition of catalase, as well as direct measurements, provided evidence of the presence and kinetic action of hydrogen peroxide as one of the intermediates. Direct addition of hydrogen peroxide resulted in shortening of the initiation stage and the propagation phase with similar rates as in the autoxidation reaction at low pH. The propagation is approximately a zero order reaction with respect to oxygen and iron. The kinetic analysis suggests that an intermediate catalytic complex(s) involving a ferryl ion (FeO²⁺) controls the rate of the propagation reaction. The Fe(III) formation shows autocatalytic behavior that mirrors the dissolved oxygen consumption patterns under all pH conditions studied. At pH values of 2.5 and 3.0, Fe(III) accumulated to a maximum, before it was partially consumed. This maximum coincided with the depletion of dissolved oxygen. The consumption of Fe(III), or the reduction of Fe(III) back to Fe(II), reflects the catalytic nature of Fe(II) and the essential role of tartaric acid in the initiation phase of Fenton’s original reaction.

The compositional authentication of wine is of great interest, as the geographic origin of the grapes is often associated with quality, uniqueness, and authenticity. Previous elemental fingerprinting studies mainly discriminated wines from different countries or regions within a country. Here, we report the use of element profiles to distinguish commercial Pinot noir wines from five sub-regional appellations or neighborhoods within one American viticultural area (AVA). Fifty-three single cultivar wines were collected over two harvests and analyzed using microwave plasma-atomic emission spectroscopy (MP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS). Of 62 monitored elements that were quantified with fully validated methods, 24 and 32 elements differed significantly across the neighborhoods and vintages, respectively (p < 0.05). Targeted canonical variate analysis (CVA) explained 85%-90% of the variance ratio across the two vintages, indicating persistent and stable elemental fingerprints of wines at a sub-regional level. A sixth, newly founded neighborhood was correctly grouped separately from the others using a Soft Independent Modeling of Class Analogy (SIMCA), indicating the potential of elemental fingerprints for wine authenticity.

The ability to model the kinetics of wine fermentation enables the early detection of abnormal, sluggish or stuck fermentations, and the prediction of present and future rates of energy, CO₂ and ethanol vapor release. While several wine fermentation models have been published, there are only a few that have been successfully adopted for commercial practice. In this work, the mathematical descriptions of wine fermentation are reviewed and compared. The common features of these include descriptions for the kinetics of yeast growth; substrate and nutrient consumption; product formation; and total and viable cell mass. Additional features include the inhibition of growth by ethanol; competitive inhibition of glucose and fructose uptake; glycerol formation; and the calculation of density from solution composition and solute properties. Three models were selected to compare their ability to describe the sugar, ethanol, biomass and nitrogen of benchtop fermentations at four temperatures, previously published. The models are assessed for their goodness of fit to the data in synthetic-medium fermentations and their suitability for analyzing and predicting commercial wine fermentations.

An in -line color and total phenolic sensor is described to track the color and total phenol evolution during red wine fermentations. The sensor uses multiple light emitting diodes (LEDs) spanning the ultraviolet and visible spectrum, in particular 280 and 525 nm. The performance of phenolic sensor was evaluated by analyzing fermentation samples collected from multiple red wine fermentations performed during the 2012 season. The study confirmed the LED phenolic sensor measurements strongly correlate with measurements performed with a reference UV-Vis spectrophotometer and that inline measurements can be made in a practical manner after removal of yeast and pulp with a 2.0 micron filter. The use of a 100 micron pathlength flow cell avoids the need for dilution, making in-line measurements possible. The sensor provides inline measurement on the evolution of the total phenolic content and color extraction patterns during red wine fermentations.