The Mason jar (aka ball jar, fruit jar, glass canning jar, Kilner jar, and lightning fruit jar) is a three-part sealing device. The three separate parts are a metal band (ring), a metallic lid, and a glass body.
The Mason jar’s glass body has a screw thread on its outer upper surface. The screw thread is what latches the metallic ring onto the glass body. The metallic lid – which has a silicone gasket installed on its one side – is fixed on top of the glass body by placing it below the metallic ring before screwing.
The Mason jar is a popular item used to can various types of high-acid and low-acid foods. The glass body is thick enough to withstand atmospheric pressure around 12 to 15 psi and temperatures above 100 degrees Celsius.
Why mason jars get rusty?
The Mason jar’s glass body will never rust because it’s made of glass. The metallic ring and lid, on the other hand, are prone to high and low amounts of rust. The rust quantity depends upon three things, material, food pH, and environment.
Most metallic lids and rings are made from Tin-plated steel. And unlike stainless steel, the Tin-plated steel is extremely weak against water. Meaning metallic lids and rings made from Tin-plated steel get rusted easily. Which is why mason jar making companies advise against using a metallic lid twice.
Acid is even more dangerous than water when it comes to their ability to rust Tin-plated steel.
The inside of a mason jar lid is coated with a chemical called Bisphenol (BSA) to protect it from acid corrosion. Because if a high-acid food is stored inside a BSA absent jar. The acid will eat through the lid, and as a result, will expose the inner contents to spoilage and pathogenic bacteria.
Humid environments have a lot of water molecules which can cause your mason jar lids and rings to rust. Long periods of storing can lead to extreme rust which can become a health hazard.
Is Rust On Mason Jar Lids Dangerous?
The rust itself is slightly dangerous although rust is iron oxide and iron oxide is not dangerous to the human body. But excessive rust can lead to improper sealing and sealing breaches, both of which are extremely hazardous.
The mason jar lids and rings are extremely cheap to buy. So we advise you to replace your lids and rings if the rust is interfering with the sealing process. If the lower side of your mason jar lid is rusted, throw it away immediately.
How to get rid of and prevent rusting?
You cannot prevent your Tin-plated rings and lids from rusting. To prevent rust, you’ll have to buy stainless steel lids and rings or plastic ones. Keep in mind that plastic lids don’t form a proper seal and are not recommended for any type of canning.
If your lids and rings are newly bought, you can use these steps to get rid of the accumulated rust.
- Place your mason jar lids and rings into a pot of warm water.
- Scrub every single rust spot with a scouring sponge. Don’t ever use a dishwasher to clean your mason jar lids and rings.
- After washing, make sure to dry them thoroughly before storing them inside a dry cabinet.