As research and development projects increasingly focus on packaging (especially closures) effects on random and premature oxidation of wine, it is timely to consider some recent findings regarding the role of bottle dimensions and its contribution to this issue.
On 12 July, the South African wine industry gathered for the first-ever Oxygen in Wine workshop, hosted by Stellenbosch University and sponsored by Cork Supply (Pty) Ltd. The speakers included renowned researchers, industry specialists, as well as students focussing on the topic at hand. All aspects of oxygen in wine, from random and premature oxidation, the effect of reductive winemaking, sparging techniques, bottling quality control protocols and the effects of oxygen and temperature, were covered in an interactive and lively workshop with attendees from all disciplines of the wine industry. The presentations included results from various Winetech funded projects.
Prof. António Ferreira, a researcher and professor in wine flavour chemistry and product development and innovation manager at Cork Supply Portugal, delivered a thought-provoking presentation regarding the effects of glass bottle variation on random and premature oxidation in wine.
What is random oxidation?
Random oxidation is bottle to bottle variation that exists due to certain factors that resulted in different amounts of oxygen in the packaged wines. This is a serious issue, especially in wines that are more susceptible to oxidation and/or wines that are intended to be aged. For these wines, a slight difference in dissolved oxygen and/or oxygen ingress can result in random oxidation. When tasted in isolation, it is impossible to say if random oxidation took place, there needs to be a comparison of different bottles from the same batch.
The formation and accumulation of various aroma compounds, as well as the deterioration of others, will inevitably occur due to random oxidation, leading to bottle to bottle aroma differences. Typical aroma compounds formed during oxidation reactions are acetaldehyde, as well as the Strecker aldehydes, such as methional (potato skin aroma) and phenylacetaldehyde (honey and floral aroma), and can play a major role in the perception of oxidation nuances. These aldehydes are often used as markers for oxidation and can be formed due to peroxidation of the corresponding alcohols by and/or via Strecker degradation of the corresponding amino acid precursor. The formation of these compounds are driven by temperature and are also affected by oxygen, metals and sulphur dioxide.
Causes of random oxidation
The direct cause of random oxidation is difficult to determine as there are many contributing factors that can lead to random and premature oxidation. It starts with the winemaker using the latest knowledge and techniques to limit oxygen dissolution in wine, the wine composition and the wine’s ability to cope with dissolved oxygen, the bottling company’s quality control parameters and the use of appropriate closure with the relevant quality and consistency.
Cork, being a natural product with natural variation, has been dubbed the main culprit when it comes to random oxidation and bottle variation. Over the past few decades, cork companies have invested substantially in research and innovation and developed methods and technology to be able to monitor and manage the variability originating from nature. However, recent studies have shifted this spotlight to other industries as well, making sure all the bases are covered. Bottling line variations and periodical malfunctions are known to lead to random and premature oxidation, while recent research showed that significant variation can also stem from the glass bottle dimensions, a parameter we have all assumed would not differ from one bottle to the next.
The role of bottle dimensions in random oxidation
Measurements of distances between the centre of the bottleneck to the inner edge of the glass showed a huge dispersion across the length of the space. This variation becomes greater at about 30 mm deep, basically setting any closure up for failure. These results are quite remarkable. A large sample set of bottles, from different manufacturers, showed not only variation between bottles from the same manufacturer (especially with the low-cost products), but also large variations between the different manufacturers.
Are these variations large enough to cause chemical variation and premature oxidation? The answer is yes, there is a significant contribution of bottleneck geometry that correlates and translates to the chemical profile of the wine that will have an impact on the sensory composition.
Join forces to tackle the issue
The main route of oxygen into a wine bottle is through the bottle and cork interface. It is therefore critical that the stopper and the bottleneck are of a minimum standard to deliver the quality of sealing necessary. The variation that occurs from either the glass, the stopper and/or bottling processes should be known, managed and minimised.
There is a risk that a specific closure (perhaps from a singular source) is more suited to a specific manufacturer’s glass bottle. While another closure, even though closure requirements adhere to the same set of standards, are more suited to an alternative manufacturer’s products. Closures also differ in their ability to handle the variations brought about the glass containers. Gaining more information regarding the variations that occur from the different sources, as well as the pro-active co-operation and investigations between the parties involved, could be beneficial for all, especially the wine producer, whose brand is directly associated with the quality of the wine.
Suggested solutions for improving the marriage between the different industries are:
- To provide information on oxygen transmission rates (or a standardised indication of oxygen permeability) on natural and technical corks.
- Appropriate quality control on the bottling line ensuring the system is finely tuned.
- Mindful winemaking.
- Improvement of glass variation.
- The development on-site measurement tools to determine all the contributing variations.
At the end of the day, the wine producer needs to have control over the quality of the bottling and ensure that the specific closures and bottles are an appropriate fit. Currently, the monitoring of glass variation, on wine producer level, is non-existent. Ferreira suggested that the ratio between the measurement at the opening of the bottle and at specific points in the bottleneck (including a point around 30 mm) be used as a standard. The number of outliers in a specified sample set, not adhering to the pre-set parameters, can be used as a benchmark for acceptability.
“None of the industries or service providers are purposefully inducing variability, however, each industry needs to strive to improve,” said Ferreira. Clearly, the different industries need to take hands to address this issue to ensure that the quality and consistency of packaged wine is on par with what the winemaker intended.
Large variations in bottle neck measurements could lead to closure failure and oxidation of the wine. The different industries need to join forces to tackle bottle to bottle variation.
– For more information, contact Dr. Carien Coetzee at firstname.lastname@example.org.