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.

Autoxidation of tartaric acid in air-saturated aqueous solutions in the presence of Fe(II) at low pH, 2.5, shows autocatalytic behavior with distinct initiation, propagation, and termination phases. With increasing pH, the initiation phase speeds up, while the propagation phase shortens and reduces to none. We show that the propagation phase is a chain reaction that occurs via activation of oxygen in the initiation stage with the production of hydrogen peroxide. The subsequent Fenton oxidation that regenerates hydrogen peroxide with a positive feedback is typical of a self-sustained chain reaction. The conditions for such a chain reaction are shown to be similar to those of a dynamical system with critical behavior; namely, the system becomes unstable when the kinetic matrix of pseudo-first-order reaction becomes negatively defined with a negative eigenvalue giving the rate of exponential (chain) growth of the reactive species.

This study investigated the effects of six cap management protocols targeting contrasting oxidation-reduction potential (ORP) evolutions during alcoholic fermentation of Pinot noir wines. Treatments included twice-daily punch-downs (PD) and pump-overs (PO), 1 h air or N₂ injections (AirMix, N₂Mix), air injections triggered by ORP ≤ −40 mV (RedoxConAir), and equal N₂ injections concurrent to RedoxConAir wines (RedoxConN₂). AirMix wines maintained ORP values above 0 mV throughout fermentation, showed an oxidatively favored glutathione-to-glutathione disulfide ratio (GSH:GSSG) of 0.3:1, and had 21% lower total phenolics and 24% lower anthocyanins than PD wines. In contrast, N₂Mix wines maintained the lowest ORP, near −100 mV, and showed a reductively favored GSH:GSSG ratio (7:1). PD wines extracted 48% more flavan-3-ols than PO wines, consistent with greater berry integrity disruption and seed submersion. Volatile composition was also impacted: ethyl n-octanoate showed the highest OAV among esters, ranging from 147 in PO wines to 116 in AirMix wines. Results suggest the GSH:GSSG ratio served as an indicator of redox history, with potential implications for color and aroma preservation during aging. Inert gas mixings resulted in equal or greater total phenolic content, while excessive air injections may provide a tool to soften astringency.

The adoption of sensors to monitor wine fermentation enables the collection of large datasets that relate the initial juice chemistry, density and temperature patterns during fermentation to fermentation outcomes. Wine kinetic models are now being applied to commercial fermentations in real time to identify abnormal or sluggish fermentations. In this work, 222 red wine fermentations from five harvests at two commercial wineries were evaluated by a wine fermentation model. The model parameters, initial juice chemistries and fermentation outcomes were analyzed for trends and relationships between them. While the fermentations with higher initial assimilable nitrogen concentrations had higher maximum fermentation rates, this did not guarantee successful fermentation outcomes in the tailing stage of the fermentation. Neither the initial, final, minimum and maximum temperatures, nor the initial pH, titratable acidity, measured yeast-assimilable nitrogen and primary amino nitrogen concentrations had any significant correlation with the maximum fermentation rate or successful completion of the fermentation. These results suggest that the initial juice-assimilable nitrogen measurements for these juices are of limited use in predicting slower and incomplete fermentation outcomes.

The estimation of parameters in a wine fermentation model provides the opportunity to predict the rate and concentration outcomes, to strategically intervene to change the conditions, and to forecast the rates of heat and carbon dioxide release. The chosen parameters of the fermentation model are the initial assimilable nitrogen concentration and yeast properties (lag time, viability constant, and specific maintenance rate). This work evaluates six methods for parameter estimation: Bard, Bayesian Optimization, Particle Swarm Optimization, Differential Evolution, Genetic Evolution, and a modified Direct Grid Search technique. The benefits and drawbacks of the parameter computational methods are discussed, as well as a comparison of numerical integration methods (Euler, Runge–Kutta, backward differential formula (BDF), and Adams/BDF). A test set of density-time data for five white and five red commercial wine fermentations across vintage, grape cultivar, fermentation temperature, inoculated yeast strain, and fermentor size was used to evaluate the parameter estimation methods. A Canonical Variate Analysis shows that the estimation methods are not significantly different from each other while, in the parameter space, each of the fermentations were significantly different from each other.