# Oxygen transfer rate measurements of closure systems after 12 years of aging. Impact on the aroma compounds of Sauvignon Blanc wines

Emilie Suhas, Cécile Thibon, Christophe Loisel, Philippe Darriet, Alexandre Pons

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Emilie Suhas, Cécile Thibon, Christophe Loisel, Philippe Darriet, Alexandre Pons. Oxygen transfer rate measurements of closure systems after 12 years of aging. Impact on the aroma compounds of Sauvignon Blanc wines. Food Packaging and Shelf Life, 2025, 48, pp.101452. 10.1016/j.fpsl.2025.101452. hal-05006540

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Submitted on 26 Mar 2025

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# Oxygen transfer rate measurements of closure systems after 12 years of aging. Impact on the aroma compounds of Sauvignon Blanc wines

Emilie Suhas<sup>a,b,d,*</sup>, Cécile Thibon<sup>a,b</sup>, Christophe Loisel<sup>d</sup>, Philippe Darriet<sup>a,b</sup>,
Alexandre Pons<sup>a,b,c</sup>

## ARTICLE INFO

### Keywords:

- Aging
- OTR measurement
- Wine shelf life
- Oxidation
- Thiols
- Carbonyls
- Dissolved gas

## ABSTRACT

Three Sauvignon Blanc wines sealed with seven closure types (natural corks, three microagglomerate corks, synthetics and two screw caps) were analyzed after 12 years of aging. OTR (oxygen transfer rate) of old stoppers (12 years) were determined by a standardized protocol using coulometry. The other analytical markers were volatile thiols and Strecker aldehydes determined by gas chromatography coupled with tandem mass spectrometry. Sulfites, dissolved CO₂ measurements and sensory analysis of the wines were also carried out. We showed that the OTR value changed after 12 years and the variability depends on the type of stoppers and ranged from 0.05 to 89.11 mg/year. The molecular markers analysed made it possible to illustrate the sensory perception of the evolution of this wine. Molecular characterisation revealed that an average OTR₁₂years of 0.27 mg/year allows preservation of thiols while delaying the formation of Strecker aldehydes whereas beyond 0.82 mg/year in average, wines develop first signs of oxidation.

## 1. Introduction

The quality of white wines aged for many years in the bottle is closely linked to their aromatic balance. The best aging conditions allow the wine to retain its varietal fruity aromas and to develop new aromatic nuances, making its expression more complex and synonymous with uniqueness, a phenomenon known as the aging bouquet.

The evolution of aroma compounds during bottle aging involves a balance of complex chemical mechanisms, such as hydration/dehydration (Pedersen et al., 2003), or hydrolysis (Sumby et al., 2010) for example, influenced by the presence or absence of oxygen. Some volatile compounds may be released from unstable forms bound to sulphites (Carrascón et al., 2017). It is now generally accepted that grape quality, winemaking practices and oak aging conditions play an important role in the production of high quality wine, while storage conditions and the stopper system are of paramount importance in the evolution of wine quality during bottle aging (Echave et al., 2021; Silva et al., 2011; Skouroumounis et al., 2005).

The wine stopper industry can be divided into three main categories

corresponding to different materials and technologies: screw caps, synthetic stoppers and cork-based stoppers (Furtado et al., 2021). Three main types of cork (Quercus suber L.) stoppers are used to seal wine bottles: natural cork stoppers, technical stoppers, including agglomerated cork stoppers (0.2–9.00 mm granulation), and microagglomerated cork stoppers (0.25–3.00 mm granulation), and stoppers (1 + 1) with an agglomerated central part and two natural cork discs glued to both ends of the stopper (Furtado et al., 2021; Gil, 2009). The first quality of a stopper is to be free of contaminants such as the 2,4,6-trichloroanisole (TCA). This means that, for these stoppers, the granules can then be washed with steam or treated with supercritical CO₂, a process that eliminates traces of TCA which can contaminate wine during storage (Taylor et al., 2000).

Stoppers also have to meet requirements in terms of liquid tightness and gas transfer modulation. The first studies carried out on the role of stoppers in the premature evolution of white wines date back to 1996 (Waters et al., 1996). Subsequently, it has been demonstrated that the stopper and its oxygen permeability plays a role in the rapid or premature evolution of wine aroma. (Godden et al., 2001; Pons et al.,

<footnote><sup>a</sup> Univ. Bordeaux, Bordeaux INP, INRAE, OENO, UMR 1366, ISVV, Villenave d'Ornon F-33140, France</footnote>

<footnote><sup>b</sup> Bordeaux Sciences Agro, Bordeaux INP, INRAE, OENO, UMR 1366, ISVV, Gradignan F-33170, France</footnote>

<footnote><sup>c</sup> Seguin Moreau France, Z.I. Merpins, BP 94, Cognac 16103, France</footnote>

<footnote><sup>d</sup> Diam Bouchage, Céret 66400, France</footnote>

<footnote>* Corresponding author at: Univ. Bordeaux, Bordeaux INP, INRAE, OENO, UMR 1366, ISVV, Villenave d'Ornon F-33140, France.
E-mail address: emilie.suhas@u-bordeaux.fr (E. Suhas).</footnote>
2021). The measurement of this intrinsic parameter corresponds to the total amount of oxygen imparted by the stopper during bottle aging (Crouvisier-Urion et al., 2018). It includes the amount of oxygen contained in the cork microstructure that is slowly released after sealing called the Oxygen Initial Release (OIR, mg). It also includes the Oxygen Transfer Rate (OTR, mg/year), which is the amount of external oxygen that enters the bottle. Recently, *Chanut et al.*, (2023) emphasized the importance of surface treatment and the stopper/bottleneck interface on the OTR.

According to Crouvisier-Urion et al., (2018) several techniques can be used to determine the OTR of closures. They differ in sensitivity and analysis time, but seem to be able to provide similar OTR values (Echave et al., 2021). The manometric technique offers a compromise between sensitivity and speed, while the coulometric technique offers the best performance in terms of sensitivity. For this reason, the latter has been historically and widely used in the packaging industry and is recommended in various standards for measuring the OTR of films. The technique was extrapolated in the middle of the 2000s for measuring the OTR of stoppers (Peck et al., 2006). The chemiluminescence method is also used in the wine industry to measure the OTR<sub>T0</sub> of stoppers, thanks to its low cost and high performance in terms of sensitivity and ease of use (Diéval et al., 2011). However, the main drawback of all these techniques is that it is impossible to monitor the evolution of the OTR of the same stopper used to seal a bottle of wine and to study its chemical and sensory evolution after many years of storage.

According to the literature, natural cork stoppers offer the most heterogeneous performance in terms of OTR values, ranging from 0.1 to more than 250 mg/year (Crouvisier-Urion et al., 2018). On average, screwcaps are the least permeable, followed by microagglomerate corks and then synthetic stoppers. Most of these OTR measurements were performed on new stoppers, with only a few used to seal wine bottles aged less than five years. However, some measurements were carried out on sections of new stoppers, while most were carried out on entire bottlenecks to study the impact of the OTR (provided by the manufacturer) on the evolution of wine aroma (< 5 years).

The knowledge and control of the OTR is of great importance for the manufacturer as well as for the end user, the winemaker. Too little oxygen may lead to the formation of reductive off-flavors (Ugliano et al., 2011), while too much will systematically cause an aromatic imbalance, accompanied by the loss of fresh fruity aromas and the development of overwhelming odors reminiscent of boiled potatoes and honeybees (Pons et al., 2021).

The specific aroma developed by young Sauvignon Blanc wines is due to the presence of fragrant thiol compounds such as 3-sulfanylhexanol (3SH) and 4-methyl-4-sulfanylpentan-2-one (4MSP) which are reminiscent of grapefruit/passion fruit, boxwood, and broom blossom, respectively (Darriet et al., 1995; Tominaga et al., 1998). Another thiol has been identified as contributing to the roasted coffee aroma of young oak aged wines (Tominaga et al., 2000) and to the aging bouquet of old Champagne (Tominaga et al., 2003b): 2-furanmethanethiol (FFT). These thiols are considered important sensory contributors because of their low detection thresholds: 60 ng/L, 0.80 ng/L, 0.4 ng/L respectively for 3SH, 4MSP and FFT (Tominaga et al., 1998, 2003a).

These compounds are very sensitive to oxidation reactions (Nikolantonaki & Waterhouse, 2012). Thiols are nucleophilic compounds with strong reactivity towards reactive oxygen species (ROS) produced through an oxidative chain reaction catalyzed by metal ions (Danilewicz, 2003). The odorant thiols trapped by the quinones lead to a reduction in their concentration and a loss of fruity notes (Nikolantonaki et al., 2014). At the same time, oxidation mechanisms contribute to the formation of aldehydes such as methional, reminiscent of boiled potatoes, and phenylacetaldehyde, reminiscent of faded roses (Culleré, et al., 2007). Their detection threshold in model wine solution was estimated to be 2.4 µg/L for methional and 30 µg/L for phenylacetaldehyde (Sarrazin et al., 2007). Both these Strecker aldehydes are derived from the breakdown of two amino acids: methionine and

phenylalanine (Grant-Preece et al., 2013). The balance between varietal aroma and oxidative notes is particularly important when evaluating wine typicity, the specific distinguishable sensory profile associated with the quality of a wine, such as sweet botrytized Semillon (Sarrazin et al., 2009), Riesling (Schüttler et al., 2015) and Chardonnay (Parr et al., 2010).

Typicity, like qualitative evolution towards bouquet expression, is a difficult concept to explain. The typicity is defined as the ability of a product (the wine) to be representative of a predefined class (Basalekou et al., 2023) and is dependent on certain parameters such as grape variety, climate or growing practices (Van Leeuwen et al., 2023). Bouquet is largely defined by the concepts of absence of defects, structure, time and the aromas that the wine will develop over time (Picard et al., 2015) under conditions that avoid oxidation defects while leaving room for different chemical mechanisms.

Grapes quality and winemaking practices are of great importance in preventing wine from aging too rapidly. However, endogenous and exogenous antioxidants such as sulfur dioxide (Skouroumounis et al., 2005), ascorbic acid (Ribéreau-Gayon, 2017) and glutathione (Pons et al., 2015) are also known to protect the wine, i.e. maintain its freshness during bottle aging. Another method is to use stoppers with a low OTR value. However, most of the studies on the influence of the stopper OTR on the evolution of the composition of white wines have been based on OTR values provided by manufacturers (OTR<sub>T0</sub>) before bottling. High OTR<sub>T0</sub> is known to affect the composition of wines during bottle aging, regardless of the variety (Sauvignon Blanc, Semillon, Riesling, Chardonnay), when the levels of dissolved carbon dioxide (DCO<sub>2</sub>), antioxidants (SO<sub>2</sub>, GSH, ascorbic acid), hydrogen sulfur and thiols decrease. On the contrary, Strecker aldehydes, sotolon and brownish color (OD<sub>420</sub>) were known to increase (Brajkovich et al., 2005; Pons et al., 2021).

Therefore, depending on the variety, geographical origin (appellation) and composition of a white wine, the influence of the stopper on its sensory evolution and composition is well known. However, we need to improve our understanding of the direct relationship between measured OTR of aged stoppers and the composition of white wines after several years of bottle aging. This experiment studied the OTR distribution of a wide range of aged stoppers (after 12 years of aging), including screw caps, natural and microagglomerate corks, synthetic stoppers, with a particular focus on their impact on the composition of a Sauvignon blanc wine and its sensory perception.

## 2. Materials and methods

### 2.1. Chemical and reference compounds

3-Octanol (> 99 %), and dichloromethane (HPLC grade), methional, and phenylacetaldehyde (98 %) were from Sigma-Aldrich (St Quentin Fallavier, France). Ultra-pure water was used in all sample preparations and model wines (Milli-Q, Millipore, Bedford, MA, USA). Anhydrous sodium sulphate (99 %) was supplied by Prolabo (Lyon, France). Ethanol (HPLC grade) was purchased from Merck KGaA (Darmstadt, Germany). 3-Sulfanylhexanol (3SH) (97 %), 2-furanmethanethiol (FFT) (99 %), 4-methyl-4-sulfanylpentane-2-one (4MSP) (95 %) were purchased from Intechim (Montlucon, France). Sulfur dioxide solution (100 g/L) was provided by Laffort (Bordeaux, France).

### 2.2. Wine samples

#### 2.2.1. Sauvignon Blanc wines selected for OTR measurements (Step 1)

The bottles of aged wine (12 years) were from three wineries in three appellations (Bordeaux, Graves, and Pessac Leognan). They corresponded to an experiment carried out in 2008 (2007 harvest) consisting in studying the influence of stopper type on the evolution of the composition of Sauvignon Blanc wines. The selection of the wines, the bottling conditions, and the type of stopper were described in detail by Pons et al., (2021) Stoppers were selected according to the OTR<sub>T0</sub>
proposed by the different manufacturers: from < 0.1–0.6 mg/year, while natural cork stoppers (unknown OTR) corresponded to those used by the winery (Pons et al., 2021). In total, 86 samples were analyzed, including 28 natural corks (NC) and 38 microagglomerate corks (12 Diam A, 15 Diam B, 11 Diam C), 11 molded synthetic stoppers (Synt), 6 Saranex and 5 Saran-tin screw caps with known OTR<sub>T0</sub> (Table 1, Step 1).

### 2.2.2. Selection for sensory analysis of aroma compounds composition (Step 2)

The second step in experiment 2 (Step 2) was carried out with 33 stoppers from Step 1 (Table 1) to study the effect of the measured OTR on the composition of the same Sauvignon Blanc wine (100%) from the Bordeaux appellation bottled in 2008 and not aged in oak barrel. This wine corresponded to one of the three vintages selected for OTR measurements. The white wine was bottled with seven types of stoppers. The entire experiment, including winemaking and bottling protocols, was previously described in detail by Pons et al., (2021). Briefly, free SO₂ and ascorbic acid were adjusted to 25 mg/L and 50 mg/L, respectively, prior to bottling. At the same time, fill level, stopper insertion depth and headspace pressure were checked and adjusted if necessary. Immediately after filling, the bottle headspace was flushed with nitrogen. Disolved oxygen (DO₂) immediately after bottling was approximately 2.3 mg/L for the two screw caps and ~1.3 mg/L for the other stoppers. Two months after bottling, DO₂ reached 10 µg/L regardless of the stopper. Finally, a sensory analysis was performed on two samples of each stopper, except for natural corks with 4 stoppers (Step 3).

### 2.3. OTR determination by coulometry

OTR measurements were performed in accordance with ASTM D1434–82 (2015) based on the protocol described by He et al., (2013) in collaboration with the LNE (Trappes, France), using a Mocon Oxtran 2/48 (Moncon, Inc. USA). Before each serie of measurements, the instrument was calibrated using the two-point method. The lowest point is zero, which was obtained by testing a stainless-steel tube. A NIST-certified Mocon calibration film was used to set the highest point. Carrier gas was a mixture of N₂/H₂ (95/5, Messer, France) at constant flow rate (25 mL/min). According to the manufacturer's specifications, the instrument was set to measure the percentage of convergence to stop the analysis when two consecutive readings differed by less than 1%, providing a detection limit of 0.00001 cm³/day (~ 0.0522 ± 2% mg/year). The temperature was recorded during the analysis and OTR was automatically calculated by the system software. The bottleneck was cut by using a Dremel® 4000 with a diamond blade (3.2 mm thick). The glass edges were then smoothed and the top, including the stopper, was bonded to a metal plate using two-part epoxy adhesive. The system allowed the inner part of the bottleneck to be flushed by the carrier gas,

while the outer part of the bottleneck was exposed to ambient air (~20% of oxygen). During measurement, the stoppers were kept in humid conditions controlled by the instrument (80–90% RH) and measured for external humidity (~50–60% RH). Finally, each OTR measurement was divided into three steps: the first for sample preparation, the second for conditioning on a degassing bench with a continuous flow of humid nitrogen (~90% RH), and the third for measurement. OTR units are expressed in mg of oxygen per cap and per day. Then OTR value were calculated in mg/year.

## 2.4. Analysis of thiols and strecker aldehydes by GC-MS/MS

### 2.4.1. Sample extraction by solid phase extraction (SPE)

The extraction protocol was based on Thibon et al., (2015) work and recently updated (Thibon et al., 2024). Briefly, 20 mL of wine samples spiked with 20 µL internal standard 3-octanol (5 mg/L EtOH) were extracted by SPE consisting of a polystyrene-divinylbenzene hydrophobic polymer (Chromabond HR-X). Volatile compounds were eluted with 3 mL of the solvent mixture pentane/dichloromethane (50/50, v/v) and 3 mL of dichloromethane/methanol (95/5, v/v), and the final organic phase was dried with anhydrous sodium sulfate and concentrated to 150 µL under a nitrogen stream.

### 2.4.2. Gas chromatography – mass spectrometry conditions

Samples were analyzed using a chromatographic system consisting of a Trace GC Ultra gas chromatograph (Thermo Electron SAS, Courtaboeuf, France) coupled to a TSQ Quantum XL triple quadrupole mass spectrometer. GC separation was performed on a Macherey-Nagel (Germany) polar wax capillary column (polyethylene glycol, 50 m; 0.25 mm; 1 µm). The autosampler (Triplus RSH autosampler) injected 1 µL of sample into a split/splitless programmable temperature injector (closing time 1 min, split flow 30 mL/min) and was set as follows: 200 °C for 1 min and rising to 250 °C at 14 °C/min and held at this temperature for 10 min. The oven temperature was initially set at 45 °C and held for 1 min, then increased to 250 °C at 4 °C/min and finally held at this temperature for 10 min. The temperature of the MS transfer line was set at 250 °C. The source parameters including source temperature, electron energy, emission current and electron lens were set at 230 °C, 25 eV, 50 µA and 100 V respectively. The collision gas was argon, and the mass spectrometer was operated in electron impact (EI) mode. The SRM conditions were optimized for each compound in terms of collision energy and gas pressure values applied to each precursor ion depending on the transition. Precursor ion (m/z), product ion (m/z) and collision energy (V) were selected as follows for compounds of interest: 3SH (134.0, 67, 5), 4MSP (132.0, 89.0, 10), FFT (114.0, 81.0, 5), phenyl-acetaldehyde (120.0, 91.0, 10), methional (104.0, 48.0, 10), and 3-octanol (101.0, 83.0, 10). Instrument setup, data acquisition, and processing

<caption>**Table 1**</caption>

Type and characteristics of stoppers selected to seal the three Sauvignon blanc wines from Graves, Pessac Leognan and Bordeaux appellations accompanied by the number of analyses carried out for OTR₁₂y measurements, chemical analysis (CA) and sensory analysis (SA).

<table><thead><tr><th rowspan="2">Stopper type</th><th rowspan="2">Code</th><th rowspan="2">Length (mm)</th><th rowspan="2">Diameter (mm)</th><th rowspan="2">OTR<sub>T0</sub><sup>a</sup> (mg/year)</th><th colspan="3">Number of sample analyzed<sup>d</sup></th></tr><tr><th>Step 1<br>OTR<sub>12years</sub></th><th>Step 2<br>OTR<sub>12years</sub> + CA</th><th>Step 3<br>OTR<sub>12years</sub> + CA+SA</th></tr></thead><tbody><tr><td rowspan="2">Screw caps</td><td>Saran</td><td>-</td><td>-</td><td>&lt; 0.1</td><td>5</td><td>3</td><td>3</td></tr><tr><td>Saranex</td><td>-</td><td>-</td><td>0.5</td><td>6</td><td>2</td><td>2</td></tr><tr><td rowspan="3">Microagglomerate corks</td><td>Diam A</td><td>44</td><td>24.2</td><td>0.3</td><td>10</td><td>3</td><td>3</td></tr><tr><td>Diam B</td><td>44</td><td>24.2</td><td>0.4</td><td>15</td><td>2</td><td>2</td></tr><tr><td>Diam C</td><td>44</td><td>24.2</td><td>0.6</td><td>11</td><td>3</td><td>3</td></tr><tr><td>Synthetics</td><td>Synt</td><td>43</td><td>22.0</td><td>0.6</td><td>11</td><td>3</td><td>3</td></tr><tr><td>Natural corks<sup>c</sup></td><td>NC</td><td>45</td><td>24.0</td><td>&lt; 0.1–283<sup>b</sup></td><td>28</td><td>17</td><td>4</td></tr></tbody></table>

<footnote><sup>a</sup> OTR<sub>T0</sub>, oxygen transfer rate provided by manufacturer (technical data sheet of the stopper) and determined by chemiluminescence (PreSens) for synthetic and microagglomerate stoppers or coulometry for screw caps. <sup>b</sup> Natural cork has a high intrinsic individual structural variability (Crouvisier-Urion et al., 2018). <sup>c</sup> Blend of natural corks from three different suppliers. <sup>d</sup> Analysis carried out on stoppers and wine samples from the different wineries according to the analytical step: step 1 included the three wineries whereas steps 2 and 3 were focused on the wine from Bordeaux appellation. OTR<sub>12years</sub>: oxygen transfer rate measured after 12 years of ageing. CA, chemical analysis. SA, sensory analysis.</footnote>
were performed using Xcalibur software (version 2.1.0). PFTBA (perfluorotri-n-butylamine) was used for mass calibration.

## 2.5. Standard oenological parameters and dissolved carbon dioxide (DCO₂)

Free and total SO₂ were measured at the laboratory according to OIV protocols. (Compendium of International Methods of Wine and Must Analysis, 2021). Absorbance at 420 nm, corresponding to yellow/-brownish color intensity, was measured with a Perkin Elmer Lambda 25 spectrophotometer. A Carbo-QC carbonation meter (Anton Paar GmbH, Graz, Austria) based on the multiple volume expansion method was used for the DCO₂ assay. Based on Pons et al., (2021), the bottle was opened (cap removed) and a 120 mL sample was carefully collected with a syringe to minimize degassing. Each measurement was performed in duplicate.

## 2.6. Sensory analysis

All sensory analysis were conducted in a temperature-controlled tasting room (20 °C) equipped with individual booths. Wines (10 mL) were presented at 16–18 °C in black “XL5-type” tasting glasses to avoid potential panel bias due to visual/taste interactions, identified by random three-digit codes and covered with plastic lids. Sample order was randomised and counterbalanced across panellists. All the white wines were tasted before being submitted to an expert in order to avoid any exogenous off-flavors such as TCA taints.

The 16 panelists had experience in tasting Sauvignon Blanc and were tasters (on average half men and half women) between the ages of 25 and 55 from the ISVV staff and from several Pessac Leognan wineries involved in this project. This resulted in an implicit consensus defining oxidation aromas (beeswax and cooked vegetables) and qualitative evolution defined as aging bouquet and terroir expectation associated with typicity. We analysed all samples during a single session and asked the panel to rate the “Sauvignon Blanc” character instead of “typicity”, and the “hedonic” level through an orthonasal evaluation only.

## 2.7. Data analysis

FIZZ software (Biosystemes, France) was used to generate the sample codes and collect the data for the sensory analysis of the monadic profiles using a tablet (FIZZ lab). Principal Component Analysis (PCA) was used to identify patterns in the data set and highlight similarities and differences whereas analysis of variance (ANOVA) and correlation tests were applied to the sensory descriptive and analytical data with XLStat (Addinsoft, France). When the ANOVA result was significant (p < 0.05), Tukey's post hoc tests were used for multiple comparison according to normality test results (Kolmogorov-Smirnov). In the particular case of non-normality of the data of log transformation was applied otherwise nonparametric Mann-Whitney test was also applied. The risk, α, was set at 5%.

# 3. Results

This study is dedicated to the analysis of numerous old Sauvignon Blanc wines in order to evaluate the impact of the OTR on their composition and sensory balance.

The first series corresponded to the analysis of the OTR of 86 stoppers corresponding to 7 different stopper groups from wines obtained from three wineries from three different appellations: Bordeaux, Graves and Pessac Leognan (Step 1). The second part of the study specifically investigated the OTR values obtained in the Bordeaux wine, with chemical analysis (Step 2). Finally, the last part made the link of OTR values, chemical composition and sensory perception (Step 3) of a Bordeaux white wine. The two natural cork batches called NC-S1 and NC-S2 were used in this part.

## 3.1. OTR determination of stoppers from aged wines (Step 1)

OTR of stoppers was assayed by coulometric method with a control of humidity during the desorption and measurement step. Indeed, according to Lagorce-Tachon et al., (2016) it should be controlled as it modifies the mechanical properties of the cork and the tightness of the stopper.

We applied the method to determine the OTR of a broad sample selection including 86 (12-years-old) stoppers of four types: 2 different screw caps, 3 different microagglomerates, synthetics and natural corks (Table 1). As depicted in Table 2, after 12 years of bottle aging, the OTRs of our selection ranged from 0.05 to 89.11 mg/year and significant differences were obtained (p < 0.05) according to closure types. The lowest values were obtained with tin-lined Saran screw caps and the highest values with the natural cork stoppers, which had the widest range of values (0.12–89.11 mg/year). These results are consistent with those reported by Crouvisier-Urion et al., (2018) on young cork stoppers.

It is interesting to compare these values with those provided by the manufacturers (OTR<sub>T0</sub>), but, as mentioned in Table 1, it is important to keep in mind that these values were obtained with different analytical techniques having different performances. Nevertheless, it is useful to understand the general trend in the evolution of stopper performance.

First, the ranking of the stopper and stopper type according to their OTR<sub>T0</sub> is consistent with the median OTR after 12 years of aging. In addition, with Saran screw caps and Diam A microagglomerate corks, OTR was close to the values provided by the supplier after 12 years of aging: 0.11 (± 0.03) mg/year and 0.53 (± 0.46) mg/year, respectively. For Saranex, the surprisingly high value might be due to mechanical damage on the surface of the screwcap during aging. In general we observed that microagglomerate stoppers Diam B and C with higher OTR<sub>T0</sub> values at 0.4 mg/year and 0.6 mg/year respectively, tend to have a higher OTR<sub>12years</sub>, probably due to reduced mechanical performance accompanied by an increase in the oxygen transfer across the interface (Chanut et al., 2021). Synthetic stoppers (Synt) with a high OTR<sub>T0</sub> (0.6 mg/year), has values after 12 years close to those given by the supplier at bottling (OTR<sub>12years</sub> = 0.86 ± 0.40 mg/year).

To our knowledge, this is the first time that the OTR of aged stoppers has been determined over such a wide range of old stoppers. In addition to the OTR values reported in this study, it is also important to note that this analysis provides an overview of the condition of the stopper at a given time. It was not possible to determine the evolution kinetics of OTR, especially for natural corks, some of which presented high OTR<sub>T0</sub> and others a high OTR after several years of aging due to a decrease in their mechanical properties. Based on these findings, we studied the influence of the OTR level of the stopper, measured after 12 years of bottle aging, on the evolution of the composition of a Sauvignon blanc

<table><caption>**Table 2**

Oxygen transfer rate of different stoppers determined by coulometry after 12 years of storage (OTR12years).</caption><thead><tr><th rowspan="2">Stopper type</th><th rowspan="2">Code</th><th colspan="4">OTR<sub>12years</sub> (mg/year)<sup>a</sup></th></tr><tr><th>Average (SD)<sup>c</sup></th><th>Median</th><th>Min</th><th>Max</th></tr></thead><tbody><tr><td rowspan="2">Screw caps</td><td>Saran</td><td>0.11 ± 0.03 (a)</td><td>0.11</td><td>0.05</td><td>0.14</td></tr><tr><td>Saranex</td><td>9.58 ± 14.67 (abcd)</td><td>0.23</td><td>0.11</td><td>31.47</td></tr><tr><td rowspan="3">Microagglomerate corks</td><td>Diam A</td><td>0.53 ± 0.46 (ab)</td><td>0.34</td><td>0.11</td><td>1.18</td></tr><tr><td>Diam B</td><td>4.09 ± 3.54 (bcd)</td><td>3.20</td><td>0.11</td><td>11.63</td></tr><tr><td>Diam C</td><td>6.17 ± 5.73 (d)</td><td>4.57</td><td>0.61</td><td>20.94</td></tr><tr><td>Synthetics</td><td>Synt</td><td>0.86 ± 0.40 (abc)</td><td>0.61</td><td>0.38</td><td>1.66</td></tr><tr><td>Natural corks<sup>b</sup></td><td>NC</td><td>15.07 ± 26.19 (cd)</td><td>3.05</td><td>0.12</td><td>89.11</td></tr></tbody></table>

<footnote><sup>a</sup> Experimental OTR values by coulometry with Mocon OX-TRAN Model 2/48. <sup>b</sup> Blend of NC stoppers from three different suppliers and wineries. Different letters in parentheses correspond to different groups at *p* < 0.05 (ANOVA, post hoc Tukey test). <sup>c</sup> average ± standard deviation</footnote>
wine by sensory evaluation and quantification of molecular markers.

### 3.1.1. Impact of OTR level after 12 years of bottle aging on chemical composition of a white wine sealed with various stopper types (Step 2)

Some samples characterised in the previous part (Step 1) were also submitted to chemical analysis to evaluate the impact of OTR₁₂years on the composition of wine (Table S1). The analysis were carried out on the Sauvignon Blanc from the Bordeaux appellation not aged in oak wood and sealed with the same stoppers as in Step 1. In total, 33 samples were selected (Table 1). For each bottle, OTR was measured and several analytical parameters were quantified, including varietal thiols (3SH, 4MSP), FFT (roasted coffee), Strecker aldehydes (methional, phenyl-acetaldehyde) OD₄₂₀ and DCO₂, and total SO₂ (Table S2). Free SO₂ was also quantified, but whatever the stopper the values were very low, below 5 mg/L. For that reason, the values were not reported and used in this part of the study. The OTR₁₂years values obtained in this stopper selection ranged from 0.16 to 59.46 mg/year, suggesting a wide range of chemical composition.

Thiols were detected at the following concentrations: tr-14.4 ng/L for 4MSP, 18.5–985.2 ng/L for 3SH, and tr-59.0 ng/L for FFT. It is interesting to note that some of the samples analyzed, originally from

the same wine, still have concentrations above the perception threshold for these three compounds, while others have seen their concentrations fall below the threshold at 0.80 ng/L, 60 ng/L, 0.4 ng/L respectively. Methional and phenylacetaldehyde concentrations were in the 0.4–110.9 µg/L and 0.9–378.0 µg/L range, respectively. Similarly, the concentrations found in the various samples after 12 years of storage can be below the detection threshold (DT) for these compounds, up to almost 50 and 12 times higher for methional (DT = 2.4 µg/L) and phenylacetaldehyde (DT = 30 µg/L). At the highest concentrations, they contribute to the aroma of wine after 12 years of aging. On the other hand, DCO₂ levels ranged from 0.13 to 0.61 g/L. The DCO₂ is regarded as a pivotal parameter in the evaluation of wines, as it significantly influences the perception of freshness even when the concentration is above the level of sub-saturation. As expected, primary evaluation of the overall data set indicated that thiols and Strecker aldehydes had opposite trends.

To summarise these trends, a Principal Component Analysis (PCA) was applied on the overall data set in Fig. 1. The first two principal components accounted for 82.95 % of the total variance: 58.49 % for axis 1 and 24.46 % for axis 2. There are two groups of parameters on the first axis according to oxidation intensity. The molecular markers known

<figure><img src="image_5.png" /><figcaption>**Fig. 1.** A: PCA biplot of aroma compound composition and OTR₁₂years values for a Sauvignon blanc wine from Bordeaux sealed with different stoppers (abbreviations are in Table 1). B: Score plots of PCA on aroma compound composition. OTR₁₂years are considered as supplementary variables. C: Cluster dendrogram of overall analytical data set obtained for the sauvignon blanc wine from Bordeaux sealed with seven different stoppers after 12 years of bottle aging (without NC 6). Sample names are indicated by stopper abbreviation followed by replicate number. Three groups were identified: G1 (green); G2 (blue) and G3 (red).</figcaption></figure>
to be correlate with oxidation (methional and phenylacetaldehyde) are represented on the left side of the PCA. The OTR values of stoppers measured after 12 years of aging, considered as supplementary variable, are plotted on the same side of the PCA as the oxidation markers. Varietal thiols and DCO₂ are on the opposite side.

A Spearman correlation test (Table S3) revealed a correlation between OTR measurements and Strecker aldehydes: 0.835 ($p < 0.01$ and 0.789 ($p < 0.01$) for methional and phenylacetaldehyde, respectively. In addition, OTR₁₂y was correlated negatively with 3SH ($r = -0.707, p < 0.01$), 4MSP ($r = -0.788, p < 0.01$), FFT ($r = -0.364, p < 0.05$) and DCO₂ ($r = -0.745, p < 0.01$). Conversely, the most oxidized samples that contained the highest Strecker aldehydes concentrations and lowest thiols and DCO₂ values were NC6, with an OTR close to 35 mg/year (Fig. 1B). However, this OTR value was not the highest that we found. It is likely that the OTR of this stopper had been very high since the beginning of this experiment, whereas the OTR of the other natural cork stoppers increased slowly during bottle aging. In other words, it was the chemical analysis that revealed the evolution, not the OTR. This outlier (NC 6) was removed from the rest of our data analysis.

Next, hierarchical clustering analysis was carried out on the overall data set except OTR₁₂years values, which were considered as a supplementary variable (Fig. 1C). The goal was to cluster the OTR₁₂years data based on the molecular composition of the white wines after 12 years of aging. The dendrogram shows classifications based on distances between samples and groups. Three groups can be established: G1, G2 and G3 (Table 3). The first group (G1, in green, OTR<sub>average</sub> = 0.27 ± 0.27 mg/year) includes wines sealed with screwcaps Saran, Diam A microagglomerate corks and two natural corks with OTR₁₂years in the 0.16–0.94 mg/year range. This group is situated on the right of the PCA and correlates with low oxidative evolution. The second group (G2, in blue, OTR<sub>average</sub> = 0.82 ± 0.73 mg/year) corresponds to stoppers with an OTR₁₂years ranging from 0.16 to 2.71 mg/year. This group includes synthetic stoppers with stable but high OTR₁₂years values since the beginning of bottle aging, as well as Diam B and Diam C microagglomerate corks with low OTR, and the Saranex screw cap. The last group (G3, in red, OTR<sub>average</sub> = 14.73 ± 20.29 mg/year) includes natural corks and Diam C with OTRs ranging from 2.10 to 59.46 mg/year. The wide range of values with the same effect may seem surprising. However, it is important to bear in mind that our analytical approach summarizes the composition of the wine but does not provide a kinetic.

To evaluate the significant differences between the three groups, a log transformation of the raw data was applied to fulfil the normality and the equality of variance necessary to apply an Anova. Thanks to this transformation, we found that the OTR₁₂years range clustered into three groups with significant differences in their distribution (Table 3). The results of the assays of the different markers obtained for the three groups were also compared (Fig. 2).

The first group (G1) differed significantly from the other two groups in terms of varietal thiols (Fig. 2 D and E, $p < 0.05$) and FFT concentrations ($p < 0.01$). This illustrates the strong reactivity of these compounds when oxygen and oxidation phenomena occur during bottle aging. On the other hand, the high OTR value group (G3) contained

<caption>**Table 3**</caption>

Oxygen transfer rate (OTR12years) values of different groups obtained according to the analysis of Strecker aldehydes, volatile thiols, dissolved carbone dioxide and clustering results (Fig. 1).

<table><thead><tr><th rowspan="2">Group</th><th rowspan="2">n</th><th colspan="4">OTR<sub>12years</sub> (mg/year)<sup>a</sup></th></tr><tr><th>Average</th><th>Median</th><th>Min</th><th>Max</th></tr></thead><tbody><tr><td>G1</td><td>8</td><td>0.27 ± 0.27 (a)</td><td>0.16</td><td>0.16</td><td>0.94</td></tr><tr><td>G2</td><td>13</td><td>0.82 ± 0.73 (b)</td><td>0.70</td><td>0.16</td><td>2.71</td></tr><tr><td>G3</td><td>11</td><td>14.73 ± 20.29 (c)</td><td>6.10</td><td>2.10</td><td>59.46</td></tr></tbody></table>

significantly more Strecker aldehydes (Fig. 2, B, $p < 0.01$ and C, $p < 0.001$) and lower DCO₂ ($p < 0.01$) concentrations than the other two groups. Therefore, based on these findings, it seems that after 12 years of bottle aging, the OTR₁₂years of stoppers shows that an OTR<sub>average</sub> ~0.27 mg/year is sufficient to maintain a high thiol content in the wine while delaying the formation of oxidative by-products and around 0.82 mg/year, the first signs of oxidation were observed by the loss of FFT and 4MSP.

During bottle storage, incoming oxygen rapidly reacts with phenolic compounds, triggering a cascade of chemical reactions that lead to the trapping of varietal thiols with an increasing reactivity kinetic 3SH < 4MSP < FFT (Nikolantonaki et al., 2010). As a result, the addition of large amounts of oxygen to the wine initially leads to a rapid reduction in thiols in the wines down to trace levels, as observed here. In parallel, the chemical mechanisms involved in the trapping or degradation of thiols is accompanied by an increase in the formation of Strecker aldehydes. An oxidative reaction takes place in wines according to a hierarchy of mechanisms described previously (Nikolantonaki & Waterhouse, 2012), with antioxidants, H₂S, thiols and the synthesis of compounds such as Strecker aldehydes being the preferential mechanisms.

When wines are stored in bottles for long periods, the amount of oxygen accumulated by the closure system is critical in limiting these oxidative mechanisms. For the preservation of this Sauvignon Blanc from Bordeaux appellation, it is therefore essential for the cork manufacturer to offer closures that can guarantee a gas permeability of less than 0.82 mg/year, maintained over a long period.

### 3.1.2. Impact of OTR level after 12 years of bottle aging on sensory and chemical composition of a white wine sealed with various stopper types (Step 3)

The last part of this study (Table 1, Step 3), including sensory analysis and supplementary analytical data was carried out on a Sauvignon Blanc wine from the Bordeaux appellation with a smaller selection of stoppers ($n = 20$). It includes five screw caps, eight microagglomerate and four natural corks and three synthetic stoppers (Table S1) having very low and very high OTR₁₂years, (from 0.16 to 59.46 mg/year) as depicted in Table S2. Sensory analysis was also carried out with a range of descriptors including oxidation, aging bouquet and intensity of the Sauvignon Blanc character.

The overall data set (Fig. S1) was analyzed by principal component analysis. The PCA explained 81.17 % of the total variance, with PC1 and PC2 explaining 63.94 % and 17.23 % respectively. Projection of variables shows that the horizontal axis illustrates the oxidative evolution of the wine samples. The results, including new sensory data and total SO₂ levels, are in total agreement with the previous data set (Fig. 1). High OTR induced a decrease in thiols and total SO₂ as well as the formation of Strecker aldehydes and finally the modification of the sensory balance of the wine: from fresh fruity aromas to overwhelming odors associated with oxidative evolution. In addition, aging bouquet and hedonic characters were correlated with varietal thiols and FFT.

Table 4 shows a Spearman's correlation matrix for this data set to compare analytical and sensory results. After 12 years of aging, there was significant strong correlation for some of them. For example, the strongest correlation (absolute value) for the sauvignon descriptor was with 3SH ($r = 0.749, p < 0.01$) and OTR₁₂years ($r = -0.639, p < 0.01$). For oxidation it was OTR₁₂years ($r = 0.716, p < 0.01$) and 3SH ($r = -0.898, p < 0.01$). Strong correlations for aging bouquet were also obtained with 3SH ($r = 0.777, p < 0.01$) and OTR₁₂years ($r = -0.537, p < 0.01$) whereas 3SH ($r = 0.780, p < 0.01$) and OTR₁₂years ($r = -0.632, p < 0.01$) correlated strongly with the hedonic perception of these aged white wines. Of course, an increase in Strecker aldehydes was associated with a significant increase in oxidation level (methional $r = 0.63, p < 0.01$; phenylacetaldehyde $r = 0.44, p < 0.05$) accompanied by a significant lower total SO₂ concentration ($r = -0.809, p < 0.01$). The OTR level of the stopper after 12 years of aging is of particular

<footnote><sup>a</sup> Experimental OTR values by coulometry with Mocon OX-TRAN Model 2/48. Different letters in parenthese correspond to different groups at $p < 0.05$ (ANOVA, post hoc Tukey test).</footnote>
<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Distribution of analytical parameters according to clustering of data in three different groups: G1 (OTR<sub>12years</sub> = 0.27 ± 0.27 mg/year, n = 8), G2 (OTR<sub>12years</sub> = 0.82 ± 0.76 mg/year, n = 13) and G3 (OTR<sub>12years</sub> = 14.73 ± 20.29 mg/year, n = 11): A: DCO<sub>2</sub>, B: methional, C: phenylacetaldehyde, D: 3SH, E: 4MSP, F: FFT. Different letters correspond to significant different groups (ANOVA, post hoc Tukey test). Horizontal line corresponds to median value of distribution.</figcaption></figure>
<table><caption>**Table 4**
Correlation coefficient between molecular markers, and OTR measurement and sensory characters of a Sauvignon Blanc wine sealed with different stopper types (N = 20).</caption><thead><tr><th>Variables</th><th>OTR 12years</th><th>4MSP</th><th>3SH</th><th>FFT</th><th>Methional</th><th>Phenylacetaldehyde</th><th>DCO<sub>2</sub></th><th>Total SO<sub>2</sub></th><th>Descriptors<sup>a</sup><br>Sauvignon</th><th>Oxidized</th><th>Aging Bouquet</th><th>Hedonic</th></tr></thead><tbody><tr><td>OTR, 12years</td><td>1</td><td>-0.629 **</td><td>-0.662 **</td><td>-0.342</td><td>0.672 **</td><td>0.545<sup>*</sup></td><td>-0.710 **</td><td>-0.809 **</td><td>-0.639 **</td><td>0.716 **</td><td>-0.537<sup>*</sup></td><td>-0.632 **</td></tr><tr><td>4MSP</td><td></td><td>1</td><td>0.826 **</td><td>0.725 **</td><td>-0.629 **</td><td>-0.498<sup>*</sup></td><td>0.524<sup>*</sup></td><td>0.821 **</td><td>0.588 **</td><td>-0.752 **</td><td>0.654 **</td><td>0.498<sup>*</sup></td></tr><tr><td>3SH</td><td></td><td></td><td>1</td><td>0.765 **</td><td>-0.639 **</td><td>-0.432</td><td>0.602 **</td><td>0.843 **</td><td>0.749 **</td><td>-0.898 **</td><td>0.777 **</td><td>0.780 **</td></tr><tr><td>FFT</td><td></td><td></td><td></td><td>1</td><td>-0.415</td><td>-0.205</td><td>0.201</td><td>0.614 **</td><td>0.559<sup>*</sup></td><td>-0.626 **</td><td>0.756 **</td><td>0.535<sup>*</sup></td></tr><tr><td>Methional</td><td></td><td></td><td></td><td></td><td>1</td><td>0.904 **</td><td>-0.753 **</td><td>-0.779 **</td><td>-0.520<sup>*</sup></td><td>0.630 **</td><td>-0.451<sup>*</sup></td><td>-0.508<sup>*</sup></td></tr><tr><td>Phenylacetaldehyde</td><td></td><td></td><td></td><td></td><td></td><td></td><td>-0.579 **</td><td>-0.617 **</td><td>-0.337</td><td>0.463<sup>*</sup></td><td>-0.191</td><td>-0.364</td></tr><tr><td>DCO<sub>2</sub></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td><td>0.585 **</td><td>0.431</td><td>-0.541<sup>*</sup></td><td>0.455<sup>*</sup></td><td>0.496<sup>*</sup></td></tr><tr><td>Total SO<sub>2</sub></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td><td>0.745 **</td><td>-0.873 **</td><td>0.617 **</td><td>0.659 **</td></tr><tr><td>Sauvignon</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>-0.838 **</td><td>0.820 **</td><td>0.836 **</td></tr><tr><td>Oxidized</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td><td>-0.711 **</td><td>-0.823 **</td></tr><tr><td>Aging Bouquet</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.678 **</td></tr><tr><td>Hedonic</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr></tbody></table>

importance when studying the composition and sensory balance of a Sauvignon Blanc wine.

## 4. Conclusion

A wide range of OTR values corresponding to young stoppers has been reported in the literature. This study has set a new milestone in the understanding of white wine evolution during bottle ageing, while reporting the first values of closure permeability using bottles stored in a cellar in controlled conditions for over a decade. The methodology used was standardized (ASTM D1434–82, 2015) and adapted to wine closures. In terms of oxygen permeability, only Saran tin screwcap and Diam A microagglomerated cork showed, simultaneously, low and consistent OTR values. The OTRs measured after 12 years of other microagglomerated cork and Saranex screwcap cover a wider range of OTR levels, whereas natural corks showed the widest OTR range from 0.12 to 89.11 mg/year. In addition, we confirmed that the permeability value of the closures has a strong impact one the sensory balance and the fine chemical composition of the white wines: Strecker aldehydes, 3SH, 4MSP, FFT. However, based on our analytical approach we were able to go further and to define three clusters in terms of OTR values: below an average OTR<sub>12years</sub> ~0.27 mg/year, thiols are preserved, close 0.82 mg/year first signs of oxidation were observed and beyond 14.73 mg/year wines are oxidized. These results constitute the first work on the evaluation of the long term effect of measured OTR on the quality of Sauvignon Blanc wines and can help the winemaker to choose the right OTR value to preserve the quality of its Sauvignon Blanc wine during bottle aging. Further work will be carried out to extend these results to other varieties.

## Abbreviations

OTR: oxygen transfer rate; PCA: principal component analysis; HPLC: high performance liquid chromatography; TCA: 2,4,6-trichloroanisole; 3SH: 3-sulfanylhexanol; FFT: 2-furanmethanethiol; 4MSP: 4-methyl-4-sulfanylpentane-2-one; EDTA: Ethylenediaminetetraacetic acid.

## CRediT authorship contribution statement

**Suhas Emilie:** Writing – review & editing, Writing – original draft, Software, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. **Thibon Cécile:** Supervision, Resources, Methodology. **Loisel Christophe:** Supervision, Resources. **Darriet Philippe:** Resources. **Pons Alexandre:** Writing – review & editing, Validation, Supervision, Resources, Project administration, Methodology, Conceptualization.

## Declaration of Competing Interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Suhas Emilie reports financial support was provided by Diam Bouchage. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Appendix A. Supporting information

Supplementary data associated with this article can be found in the online version at doi:10.1016/j.fpsl.2025.101452.

## Data availability

No data was used for the research described in the article.

<footnote>* p-value< 0.05. ** p-value< 0.01 (Spearman correlation test).<sup>a</sup> Sensory analysis tested by 16 judges.</footnote>
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