Storing Wine in Glass Versus New and Recycled PET Packaging: A Chemical Analysis

As everyone who reads this blog probably knows, wine is traditionally stored in glass bottles with a cork

seal. With the issue of climate change becoming much more dire with every passing day, new products that are more environmentally sound and sustainable are much more desired and needed.

In terms of wine packaging, there has been a lot of experimentation with different types of packaging, including bag-in-box wine and other plastic-based polyethylene terephthalate (PET) bottles. Glass bottles are heavier than bag-in-box or other plastic bottles, leading to an overall increase in the environmental footprint left by distributing and shipping these bottles all over the world. While plastics do certainly have their own issues when it comes to “environmental friendliness”, their cost of manufacturing and shipping is much lower than glass.

One problem with adopting new packaging solutions for wine relates to the ability of that new packaging to protect the wine against too much oxygen ingress, resulting in premature oxidation or other negative aromatic consequences. Another problem relates to the absorption by the packaging material of important aromatic compounds in the wine. In other words, the plastic might “suck out” some of the more desirable compounds, while allowing a lot of oxygen to pass through the material into the wine, all adding up to a potentially faulty or off-tasting wine.

A new study from the journal Food Chemistry aimed to address this issue of sensory changes in wine related to packaging materials. Specifically, the study examined the influence of packaging type on a rosé wine, comparing traditional glass bottles to plastic PET bottles and finally recycled plastic PET bottles.

Brief Methods

The wine used in this study was a rosé cinsault wine from the south of France given by UCCOAR – Val d’Orbieu. Enological parameters of the wine were: pH 3.3; ethanol 12.6%v/v; total acidity 3.4g/L; volatile acidity 0.17g/L; free SO₂ 36mg/L; and total SO₂ 130mg/L.

Wines were bottled in either glass, PET, or recycled PET, at 750mL per bottle.

All bottles were sealed with the Novatwist^TM from Novembal (a polypropylene cap with a multilayer connective joint).

Bottles were stored under 400 lux light, and at 20^oC for a total of 12 months.

Chemical analysis of the aromatic compounds in the wines occurred immediately after bottling, 3, 5, 9, and 12 months after bottling.

Results  (tip:  if you don’t care about the detailed results, just skip to the conclusion!)

• 36 different aromatic compounds were found in the rosé wine.
  • 12 alcohols, 14 esters, 6 acids, 3 lactones, and 1 ketone.

*(unless otherwise noted, all concentrations listed below are for the 12 month time period)*

Esters

• 4 esters degraded up to 50% at 5 months, and between 70% and 90% at 12 months.
• Isoamyl acetate degraded the most in the wines, losing 84% in glass bottles and 86% in both PET and recycled PET bottles.
• Hexyl acetate, ethyl hexanoate, and ethyl octanoate degraded equally in wines stored in all bottle types.
• Ethyl decanoate increased by 55% in wines stored in glass and PET bottles, but only increased by 30% in recycled PET bottles after 12 months.
  • This compound is responsible for “pleasant fruity notes” in wine.
  • The increase in wines stored in glass and PET bottles could result in increased fruity notes, though these characteristics would be less obvious in recycled PET bottles since ethyl decanoate did not increase by as much.
• Decanoic acid degraded more in wines stored in recycled PET bottles than the other two bottle types.
• Ethyl lactate increases were similar in wines stored in all bottle types.
• Diethyl-malate (D-m) and ethyl hydroxyglutarate (EH) increased more in wines stored in glass bottles than PET bottles.
  • D-m increased by 250% in glass bottles and 180% in PET bottles
  • EH increased by 550% in glass bottles and 400% in PET bottles.
    • These increases look like a lot, but since these compounds have very high odor thresholds, these increases probably didn’t do too much to the aromatic profile of the wines.
  • Diethyl tartrate formed at a higher rate in wines stored in glass bottles than in PET bottles, with differences also seen between PET and recycled PET.
  • Isopropyl-3-methylbutanoate concentrations were greater after 12 months in wines stored in PET bottles compared with glass.
  • Ethyl butanoate was 2 times higher in wines stored in recycled PET bottles.
    • This difference could result in an improved fruity quality to the rosé wines in the recycled PET bottles compared to the other two bottle types.
  • Ethyl pyroglutamate concentrations were very low in wines stored in recycled PET bottles compared to the wines stored in the other two bottle types.
  • Ethyl pyruvate concentrations increased 2 times more in wines stored in both PET bottles compared with glass bottles.
  • Total ester concentrations after 12 months increased 76% in wines stored in glass bottles, 61% for wines stored in PET bottles, and 46% for wines stored in recycled PET bottles.

Alcohols

• Alcohol degradation between the different bottle types was similar between 0 and 5 months, though significant differences were noted at 12 months.
  • At 12 months there was a 10% difference between wines stored in glass and PET bottles in regards to cis-3-hexen-1-ol.
  • At 12 months there was an almost 100% difference between wines stored in glass and PET bottles in regards to benzyl alcohol and 1-propanol.
• Isoamyl alcohol degraded by about 50% in glass and PET bottles, but only degraded by about 44% in recycled PET bottles.
  • Levels were barely above odor threshold, which could possibly have an effect on the aromatic quality of the wines.
• Methionol levels were stable in wines stored in glass bottles, but decreased by 30% in wines stored in both PET bottle types.
• Cis-2,3-butanediol levels decreased similarly in wines stored in all three bottle types.
• Hexanol levels were higher in wines store in recycled PET bottles compared with the other bottle types.
• Tyrosol formed at a slower rate in glass bottles, but was ultimately found at higher concentrations after 12 months compared with both PET bottle types.
• Total alcohol levels decreased over time for wines stored in all three bottle types.
• There appeared to be a lower protection against oxidation (by way of alcohol protection) in new PET bottles compared with recycled PET bottles.

Acids

• Hexanoic acid degradation was similar in wines stored in all three bottle types.
• Decanoic acid degradation was greater in wines stored in recycled PET bottles compared with the other two bottle types.
• Butanoic, isobutryic, and isovaleric acid increases were similar in wines stored in all three bottle types.
• 2-hexenoic acid concentrations were higher in wines stored in new PET bottles compared with recycled PET bottles.
• Total acid concentrations were relatively stable between wines stored in all three bottle types.
• Acid loses were 15% greater in wines stored in recycled PET bottles compared with the other two bottle types.

Aldehydes

• Furfural concentrations were twice as high in wines stored in both PET bottles compared with glass bottles.
  • Furfural is known to contribute to off-aromas and flavors in wine, though the differences between bottle types in this experiment were likely not enough to create sensory differences between the wines.
• Vanillin concentrations were twice as high in wines stored in new PET bottles compared with glass bottles, and 10 times lower in wines stored in recycled PET bottles compared with new PET bottles.
• Concentrations of 5-hydroxymethyl furfural were 10 times higher in wines stored in new PET bottles compared with glass bottles, though the levels still may not have been high enough to have much effect (if any) on the aroma of the wines.

Lactones

• 4-carbethoxy-γ-butyrolactone concentrations increased by 15% in wines stored in recycled PET bottles and 70% in new PET bottles.
• γ-5-hydroxy-hexalactone concentrations increased by 12% in wines stored in glass bottles, 78% in wines stored in new PET bottles, and decreased by 35% in recycled PET bottles.

Other Compounds

• Acetoin was stable between wines stored in all three bottle types.
• 2-phenyl-ethyl-acetamide and acetovanillone concentrations were stable in wines stored in glass and new PET bottles, but significantly decreased in recycled PET bottles.
• Cis-dioxane levels were 6 times higher in wines stored in both PET bottles compared to glass.
• Trans-dioxane levels were 2 times higher in wines stored in both PET bottles compared to glass.

Conclusions

The individual results of this study can be pretty overwhelming. Even if you just glanced at all the numbers and trends listed above for the wines stored in different packaging types, you might be really confused.

To put the results of this study in one sentence: there are differences between the aromatic compounds of wines stored in glass, new PET, and recycled PET bottles, however, it is not completely clear whether or not these differences matter in terms of sensory characteristics of the wines. Even between new and recycled PET bottles the results are hazy and confusing.

Many of the trends listed above are naturally occurring in wines during storage, which is evident particularly in those compounds where no differences were seen in wines from the different bottle types. It is where the concentrations of various compounds markedly differ between wines stored in different bottle types where there might be sensory differences between the finished wines.

According to the researchers, none of the compounds appeared to be different enough in terms of their odor thresholds to play much (if any) of a role in the sensory characteristics of the wines. The only way to really know for sure is to do a full scale sensory analysis, which unfortunately was not done in this case.

While I didn’t show the results here in this blog, most of the differences in chemical composition of the wines were found at the 12 month after bottling mark. Earlier on in the storage time, while there may be some minor differences here and there, there were even less than noted for the 12 month point, indicating that there may be even fewer (if any) sensory differences between the wines stored in different bottle types very early on in the storage process. I feel if the study were to continue past 12 months, we’d see an even bigger difference between the wines, possibly leading to marked differences in perceived sensory characteristics.

In general, the researchers of this study recommended that PET (either new or recycled) could be used for wines intended for consumption within 6 months after bottling or so, without any observable differences noticed in the sensory characteristics of the wine. This could lead to a decreased carbon footprint due to more environmentally-friendly shipping as a result of lower weight. Any longer than 6 months to 12 months could lead to further degradation of the wine unrelated to natural wine aging, which may result in negative influences on the sensory profile of the wine stored in PET bottles.

My biggest beef with this study is that they did not do a proper sensory analysis of the wines. Sure, they did the chemical analysis and based on known odor threshold values they were able to give an educated guess on whether or not there would be sensory differences between wines stored in glass bottles versus PET bottles, however, to be certain, it would have been valuable to include the human element as well.

As a personal aside, I have several problems with plastics (see why here on my sister site, Stealth Epidemic) and thus do not overtly recommend everyone switching to all plastic bottles without doing more inquiries, but with the proper research and development, a solution that is safe and sound (and tasty!) for everyone and the environment can be achieved.

What do you all think of this study? IF you make wines that are designed for consumption within the first year, would you switch to PET bottles? Why or why not? For consumers, would you drink wine from a PET bottle given the results of this study? Why or why not?

Please feel free to comment!

Source:

Dombre, C., Rigou, P., Wirth, J., and Chalier, P. 2015. Aromatic evolution of wine packed in virgin and recycled PET bottles. Food Chemistry 176: 376-387.