Alternatives to glass for wine packaging: Can plastic perform?(1)
In this age of environmental awareness, the wine industry is frequently tuned in to environmentally-friendly alternatives to the status-quo. For example, wineries have been known to recycle their wastes for animal feed, fertilizer, or even pharmaceuticals, in addition to reevaluating how their wines are distributed to customers. One side of the wine business that is starting to garner more attention is the packaging aspect. Wine is not only packaged in glass bottles, but also in plastic bags, plastic bottles, and even cans.
Studies and speculation have shown, however, that the type of packaging used may influence the overall quality of the wine, which ultimately relates to the gas exchange between the wine and the atmosphere through the packaging. The oxidation of wine, while important to the overall character of the wine at certain rates, may cause a loss of aromatic quality, the degradation of anthocyanins and tannins, and the appearance of a brown precipitate if too much oxygen is present.
In recent years, a particular type of plastic has been developed to potentially help reduce the amount of oxidation in wines caused by poor packaging materials. PET, otherwise known as polyethylene terephthalate, belongs to the polyester family, and has been developed for preservation of foods and beverages (sodas, juices, water, and now wine). Chemically, PET is a combination of ethylene glycol and terephthalic acid, which form a polymer chain. This chain is then broken down into small pellets, then heat applied to create a liquid which may then be formed into any desired shape. Advantages to this type of material are cited as being transparent, low cost, and strength. As a result of this technology, PET has been considered a potential acceptable replacement for glass, available in both single-layer and multi-layer forms.
The PET multi-layer form was developed in an attempt to improve the gas barrier properties of the container, and consists of a three layer structure of PET – Gas Barrier Resin – PET, or a five layer structure of PET – Gas Barrier Resin – PET – Gas Barrier Resin – PET. The gas barrier resin could be created using many compounds, with one example being an ethylene-vinyl alcohol copolymer and MXD6 nylon. One potential environmental concern with the multi-layered PET containers is that the present of the polymers in the different layers make recycling more difficult and more expensive. Boxed wine (i.e. Bag in Box®) uses similar technologies as PET, with multiple layers as described above. To protect the bag, a cardboard box is employed. Some studies have shown that PET bottles are capable of storing a wine up to 7 months, and are successful in slowing down the transfer of oxygen that would otherwise cause wine quality decay.
The study reviewed today, which is currently available only in online form until the publication comes out in January 2012, aimed to study the decay of quality in both white and red wines in different packaging types (glass bottles, PET multi-layer bottles, PET mono-layer bottles, and Bag in Box®) and different volumes (18.5cL and 75cL for bottles, and 300cL for Bag in a Box®).
Methods
The wines sampled were both red and white Bordeaux blends from the 2008 vintage. All bottling occurred via standard approved methods, and a screw cap was the chosen closure.
For the packaging, glass bottles, mono-layer PET (0.3mm thickness), multi-layer PET (0.4mm thickness), and Bag in Box® were used.
All wine samples were stored upright at 20 degC for 18 months.
Oxygen levels were measured using a chemical electrode oxygen Probe. Carbon dioxide levels were measured using the multiple expansion method. The following standard enological parameters were also measured: titratable acidity, volatile acidity, alcohol content, pH, microbiological characteristics, color characteristics, and sulfur dioxide.
Thiols were measured using gas chromatography and mass spectrometry.
For each treatment (i.e. each wine in each packaging type), samples were collected and analyzed just after bottling, and then again at 3, 6, 9, 12, and 18 months.
Sensory analysis of the wines occurred just after bottling, in addition to after 6, 12, and 18 months of aging. The panel consisted of 25 experts (researchers and PhD students of the faculty of enology at the Université de Bordeaux). Analysis took place in a standard tasting room with private booths, with wines assessed at 20oC (smell and taste). For white wines, the descriptors analyzed were limpidity, color intensity, sauvignon character, and oxidative and reduction evolutions. For red wines, the descriptors analyzed were color intensity, evolution of the color, fruity character, oxidative evolution, reduction, astringency, and bitterness. All attributes were scored on a scale from 0-5.
Results
White Wine
Oxygen:
The initial concentration of oxygen was 0.73mg/L
For glass bottles and multi-layer PET (75cL), the oxygen content decreased quickly in the first three months, then remained stable and very low.
For multi-layer PET (18.5cL) and Bag in Box®, the oxygen content was around 0.5mg/L.
For mono-layer PET, the oxygen content was high around 1mg/L for the 75cL bottle and 2.5mg/L for the 18.5cL bottle after 12 months.
