Here is a brief overview taken from The Natural Canning Resource Book:
Jarden Home Brands (Jarden Corporation) currently has a monopoly on most commercial canning jars in the US and Canada, owning the Ball®, Kerr®, Golden Harvest®, and Bernardin® Mason jar lines. Canning lids, like more than 99% of steel food cans, have inner plastic polycarbonate linings which prevents the food, especially high acid foods, from reacting with the metal. The lids also have a soft rubber sealing compound around the underside edge which is used to form the vacuum seal. There are two serious health concerns about metal canning lids:
- The endocrine disruptor bisphenol A (BPA) is used to form the plastic lining on the underside of the lids.
- There are phthalates (AKA plastisol) in the rubber sealing compound. Phthalates are also endocrine disruptors.
Endocrine disruptors mimic estrogen. They are linked to sexual development problems in children and breast cancer in women. While many toxic substances are more dangerous in high doses, the opposite is true for endocrine disruptors; low doses pose more of a health risk. Hormone-mimicking chemicals have effects at levels of a few parts per trillion. “BPA tests show that low doses can be the most toxic of all, below the radar screen of the body’s compensatory detoxifying mechanisms,” says the Environmental Working Group.
Tattler Reusable Canning Lids, the canning Holy Grail?
This reusable plastic lid is compatible with American glass canning jars and, according to the company, is “infinitely reusable”. Tattler lids are made of polyoxymethylene copolymer. Coplymers are linked plastics which contain two or more ingredients. In this case the copolymer is made from a trimer of three formaldehyde molecules joined together in a ring called trioxane. Formaldehyde is highly toxic and has long been known as a carcinogen.
So which is worse, bisphenol-A or polyoxymethylene copolymer? Who knows? No one has compared them in published, peer-reviewed research. Both are released at high heat and, so, will leach into food at canning temperatures.
A third alternative is the European-style canning jars with rubber gaskets; the most popular is the German Weck® jars. These are not USDA approved because they have not been evaluated in USDA laboratories and the USDA will likely never accept European research despite the fact that the EU generally has a better food safety record than the US. The glass lids are non-toxic, reusable and recyclable but the rubber gasket should be replaced each time you can. The synthetic rubber in the gasket is a petrochemical product and, like PBA and phthalates it is also an endocrine disruptor. However, in this canning system, the rubber never comes in contact with the food since the ring sits on the outer rim of the jar. There is a lack of scientific research regarding pressure canning of low acid foods using this method so it is impossible to ensure that USDA processing times are sufficient.
Fro more information, greater detail and references, please see: