When you get your wine from a box, you know you're not getting the best quality. And that's not just because of appearances. Certain materials cause a process called "flavor scalping," which draws certain chemicals right out of the food.
Right here on the site, we've seen that wine tasting is worthless guesswork, but our tongues are still good for a few things. They may not be able to tell the subtleties of a wine, but they can tell which wine has been kept in a bottle and which wine has been kept in a plastic pouch. For that matter, they can tell which juice has been kept in a bottle and which in a plastic pouch. Food companies, wanting to put their food in a package that is lightweight and durable, often encounter a phenomenon known as "flavor scalping."
When you in put them close proximity, two chemicals will often interact. Food companies noticed that some of the aromatic compounds which gave juice its freshness simply disappeared after being stored in certain kinds of plastics for a while. Wine also lost its more subtle flavors - such as fruit, honey, smokiness.
When dealing with flavors, you'll see the word "ethyl" a lot. Ethyl groups consist of two carbon atoms, one of which has three hydrogen atoms hanging on to it, and one of which has two. Compounds with this group are made by mixing different ethanols with different acids, and they result in flavors from pineapple (ethyl butanoate) to smoke (4-ethylphenol).
The flavor compounds are nonpolar molecules. Polar molecules, like water, are molecules that hold their atoms in such a way that one side of the molecule is slightly positive from an exposed proton and one side is slightly negative due to a cluster of electrons. Polar molecules tend to interact with other polar molecules. Nonpolar molecules, in which charge is very evenly distributed, tend to interact with other nonpolar molecules. The most common plastic today is polyethylene, and if you look at the name, you'll be able to guess at how it interacts with the other "ethyls." Studies show that polyethylene either absorbs these flavors, or lets them escape, while keeping the polar molecules, like water, firmly and blandly trapped in the bag of wine.
Top Image: Linh Tinh