Plastic Bottles for Wine -
is there a leaching problem?
I have been asked by a number of people, some of them home brewers, about the safety of using plastic bottles for storing wine. Their worry is that chemicals may leach out of the plastic bottle (made from polyethylene terephthalate or PET, a polyester) on prolonged contact with alcohol and cause harm.
PET is made from ethylene glycol and terephthalic (para-phthalic) acid. Some plastics contain added plasticisers; these are compounds which make the plastic less brittle.
The main worries are these:
- Plasticisers may leach out. Some of these are known endocrine disruptors, e.g. ortho phthalate esters mimick female hormones.
- Unreacted monomer (the materials from which the plastic is made) or other compounds formed when the plastic is made may leach out.
- Alcohol is a good solvent. Will this make the compounds leach out more quickly?
I have some experience as a chemist, and offer the following comments:
1)PET contains no plasticisers, so there is no danger from ortho phthalate esters.
2)Leaching of ethylene glycol and terephthalic acid is to be expected to some extent.
3)Terephthalic acid is insoluble in water but slightly soluble in alcohol. If it leaches out of the plastic it will do so more quickly into alcohol (or wine) than water.
PET also contains detectable amounts of acetaldehyde, which is able to migrate from the polymer into liquid media to the extent of a few mg per kg of bottle contents.
EVIDENCE (from a brief internet search)
Migration of ethylene glycol (EG) from PET bottles stored at 32°C for 6 months into the food simulant 3.0% acetic acid has been studied. Levels were about 94 µg/bottle.
Migration from colored PET bottles for carbonated beverages has been studied. PET bottles filled with naturally carbonated mineral water for 6-months released acetaldehyde, dimethyl terephthalate, and terephthalic acid, in amounts below FDA and EEC permitted limits.
19 compounds leaching from commercial amber PET bottles have been identified at very low concentration.They appear to be byproducts of the polymerisation reaction or intermediates.
Migration of residual contaminants remaining in the extruded PET (benzene, butyric acid, dodecane, octadecane, tetracosane, diazinon, lindane, and cooper ethyl hexonate) into food-simulating solvents, aqueous ethanol, and heptane, resulted in concentrations lower than 0.01 mg/kg after six months.
CONCLUSIONS
Ethylene glycol at 94 µg/bottle is not a problem; it's not particularly harmful in dilute solution.
Acetaldehyde is present in wine already, and is therefore not a problem.
As for dimethyl terephthalate and terephthalic acid, the picture is not so clear. There appear to be harmful effects of phthalic acid on rats at extremely high concentration, but that's exactly what one would expect; most chemicals affect living creatures if present in large amounts. At the concentrations caused by leaching, however - about a tenth of a milligram per bottle by my extimate - there seems to be no evidence, at present, of any harmful effect on people or wildlife.
A number of major retailers are now selling wine in plastic bottles. They must perceive the risk in doing this, even for prolonged storage (many years), to be somewhere between negligible and zero.
No government agency has accepted the possibility of harm from these low levels of exposure. U.S. FDA (1998) approved the use of PET as components of polyethylene phthalate polymers intended for use in contact with food in accordance with the conditions prescribed in 21 CFR part 177.1630.
My own view: PET bottles seem pretty safe, even if used and re-used for years. At the risk of overkill, however, I recommend:
-
a)Don't store wine for many years in plastic. Use it after a year or two.
b)Store the wine in the dark so that the plastic doesn't degrade.
c)Keep the bottles in a cool place.
d)Use glass for long-term storage (several years or more) if you're a home brewer.
Remember also that glass isn't without its hazards. Storing any liquid containing sugar in a sealed glass container can result in violent explosions. This is why (as a winemaker) I switched to plastic bottles in the first place.
If you are a chemist or researcher and would like to supply information to improve this article, please send me an email: diversity@suttonelms.org.uk
N.D.
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