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 present study examined the effect of different cap management techniques, maceration length, and ethanol levels through chaptalization on the chemical and sensory composition of Syrah wines from the Edna Valley AVA in California. Punch down wines had significantly higher anthocyanins, tannins, and total polymeric pigments compared to all other treatments. In terms of volatile chemistry, the submerged cap wines tended to have a higher concentration of esters and terpenes compared to the other treatments. Additionally, ethanol levels were more impactful on the chemical composition of the wines. As expected, chaptalized wines had significantly higher ethanol and glucose + fructose levels but also tended to have higher concentrations of esters and terpenes. Sensory evaluation was done through a modification of the Pivot© Profile method using an expert panel of winemakers (n = 15). The results suggested that cap management and the maceration length were more impactful on the sensory profile than the ethanol level whereby each cap management and maceration length treatment had a distinctive profile. As such, the punch down, chaptalized wines showed higher purple hue and color saturation attributes, blueberry orthonasal aromas as well as jammy and black fruit retronasal aromas. Submerged cap wines were associated with significantly meatier orthonasal aromas and reductive retronasal aromas. Extended maceration wines were characterized by more jammy orthonasal aromas and dried fruit retronasal aromas. However, within the extended maceration wines, the effect of chaptalization was apparent whereby the chaptalized wines showed more acetaldehyde aromas while the non-chaptalized wines were characterized by more herbal aromas.

To further understand redox mechanisms occurring in wine, caffeic acid (CAF, 150 mg/L) and/or glutathione (GSH, 150 mg/L) were added to a model wine solution, followed by ferric iron (2 mg/L Fe(III), added as 10 mg/L Fe(III) chloride hexahydrate), while monitoring the oxidation–reduction potential (ORP, redox potential). Caffeic acid produced only modest ORP changes. In contrast, glutathione and caffeic acid + glutathione additions dropped the ORP from 243 mV and 238 mV, respectively, to the same post-addition value of 189 mV, suggesting that glutathione dictated the ORP, while caffeic acid showed no effect. The quinone of caffeic acid (assumed as changes in AU at 420 nm), was not detected, suggesting caffeic acid did not participate in oxidation reactions under wine conditions under superfluous amounts of dissolved oxygen (DO). After the addition of Fe(III), ORP increased to similar values across all treatments: 266 mV (FE), 269 mV (CAF), 284 mV (GSH), and 242 mV (CAF + GSH), suggesting that the Fe(II)/Fe(III) redox couple dominated the ORP electrode response. CAF + GSH produced the steepest ORP decline after the addition of Fe(III) chloride hexahydrate (β (slope of the ORP) = −0.7082), significantly steeper than FE (β = −0.3051; p = 0.0032) and GSH (β = −0.4643; p = 0.0496), suggesting synergistic radical quenching and metal redox cycling. Photo-Fenton-like reactions likely contributed to slight decreases in the ORP over time. In conclusion, glutathione strongly lowered the ORP, Fe(III) increased the ORP across treatments, and caffeic acid had minimal impact on the ORP under model wine conditions.

The aim of this study was to investigate the effects of thermo-maceration and apple pomace addition on phenolic compound extraction during cider fermentation and on the volatile profile of the final product. Jonagold apples were milled, and the juice was divided into four groups: (1) Control: no apple pomace or thermo-maceration; (2) Control TM: thermo-maceration only; (3) CiderAP: apple pomace addition only; and (4) CiderAPTM: apple pomace addition combined with thermo-maceration. Apple pomace was added at 50% of the average pomace weight created during milling, and thermo-maceration consisted of heating the juice to 60 °C for 1 h prior to fermentation. Ciders were fermented at 20 ± 1 °C for 14 days. CiderAP and CiderAPTM showed higher total phenolic content (TPC) and antioxidant activity than the control treatments. The volatile profile was also modified, with CiderAPTM showing the highest phenylethyl alcohol concentration and esters exhibiting compound-specific responses. Statistical analysis showed that only apple pomace addition significantly increased TPC and antioxidant activity, while both apple pomace addition and thermo-maceration affected the volatile profile. Under the conditions evaluated, thermo-maceration did not increase TPC or antioxidant activity beyond the effect of apple pomace addition but did modify the volatile profile of the ciders. Further research should evaluate different thermo-maceration temperatures and durations to determine its potential application in cider production. The findings of this study provide valuable insights for cider makers on the valorization of apple pomace and potential use of thermo-maceration in cider production.

Sulfur dioxide (SO₂) is a preservative used in the production of fermented beverages for its antimicrobial and reducing properties. However, its effect on the oxidation–reduction potential (ORP, redox potential) during alcoholic fermentation of apple cider has never been recorded. In this study, freshly pressed apple juice was fermented with a 30 mg/L free SO₂ addition (RED) and without an SO₂ addition (CON) prior to alcoholic fermentation. Fermentation kinetics, ORP, basic chemistry, organic acids, nitrogenous compounds, free and total SO₂, glutathione (GSH), phenolics, and volatiles were monitored during alcoholic fermentation and at racking. Additionally, sensory analysis was conducted after bottling. Sulfur dioxide had no effect on fermentation kinetics, nitrogen utilization, ethanol yield, or the volatile composition of the apple ciders at racking. The ORP (vs. Ag/AgCl reference electrode) reached maximum values of 310 mV in CON and 218 mV in RED before alcoholic fermentation, and minimum values of −94 mV and −136 mV, respectively, near peak alcoholic fermentation. Mean ORP values during alcoholic fermentation were −29 mV in CON and −47 mV in RED. No statistical differences were found between the ORP of CON and RED using net area under the curve (AUC) of the ORP relative to Y = 0 mV, nor in the GSH chemistry of the ciders. The addition of SO₂ inhibited malolactic fermentation (MLF) during alcoholic fermentation. As a result, higher concentrations of malic acid and lower concentrations of lactic acid were observed in RED than in CON at racking. Sulfur dioxide additions preserved monomeric, dimeric, and increased the pool of sulfonated flavan-3-ols, likely due to PPO inhibition during the prefermentative phase and reactive oxygen species (ROS) quenching. The sensory composition of the ciders was affected whereby CON showed higher banana aroma and RED trended towards reduction aromas. Overall, SO₂ additions before alcoholic fermentation of apple cider preserved phenolics, inhibited MLF, and increased reduction aroma with no clear effect on fermentation kinetics and ORP, highlighting trade-offs between the impact of SO₂ additions on the chemical and sensory attributes of apple cider.

Sulfur dioxide (SO₂) is an antimicrobial and reductant used in the production of fermented beverages. Its effect on the oxidation-reduction potential (ORP) during alcoholic fermentation of apple cider has never been recorded. In this study, apple juice was fermented with a 30 mg/L free SO₂ addition (RED) and without (CON). Fermentation ki-netics, ORP, basic chemistry, organic acids, nitrogenous compounds, free and total SO₂, glutathione, phenolics, and volatiles were monitored, and sensory analysis was conducted. Sulfur dioxide had no effect on fermentation kinetics, nitrogen utilization, ethanol yield, or the volatile composition of the apple ciders. The ORP (vs. Ag/AgCl reference electrode) reached maximum values of 310 mV in CON and 218 mV in RED before alcoholic fermentation, and minimum values of –94 mV and –136 mV, respectively, near peak alcoholic fermentation. Mean ORP values were –29 mV in CON and –47 mV in RED, but no differences were found between the ORP of CON and RED using net area under the curve (AUC). SO₂ preserved monomeric, dimeric, and increased the pool of sulfonated flavan-3-ols. The sensory composition of the ciders in CON showed higher banana aroma whereas RED trended towards reduction aromas. SO₂ additions in apple cider preserved phenolics, inhibited MLF, and increased reduction aroma with no effects on fermentation kinetics and ORP.