Mason Jars: Your Questions Answered

Mason Jars: Your Questions Answered

September 02, 2022

Mason Jars: Your Questions Answered

What Are Mason Jars?

Mason jars are glass jars that have an airtight screw-on lid specifically made for home canning and preserving. These lids have a unique design which includes two parts that help seal the jars shut when subjected to heat through a water bath canner or a pressure canner.  

The first part is a lid with a rubber ring that allows for an airtight seal (designed for single use), and the second is the outer band with screw threads to tighten the lid to the jar (reusable). Canning with this method allows people to create preserves easily (and safely). 

In the United States mason jars come in two standard sizes: Regular Mouth and Wide Mouth.  The diameter of a regular mouth mason jar opening is 2 3⁄4 inches (70 mm) measured on the outside of the jar. A wide mouth mason jar opening is 3 3⁄8 inches (86 mm) measured on the outside of the jar.  These sizes are universal and identical across brands, as well as, various volumes of jars.  This makes mason jars very useful, because the lids are interchangeable.

The volumes of mason jars are also standard, however the shapes can vary.  Volumes of jars range from 4 oz., all the way up to 64 oz.  The most common sizes are pints (16 oz.) and quarts (32 oz.).

Mason jars have many uses, from décor to drinks and even syrup dispensers. With our mason jar accessories you can give your mason jars new functionality for your kitchen.

2 mason jar with lids.  One is open.

Where Did Mason Jars Come From?

Mason jars with screw tops came about 50 years after the creation of canning in the middle of the 19th century.  A tinsmith named John Landis Mason created the two part lid and filed a patent in 1858.  The invention helped smooth the process of home canning and preserving foods by making the task easier, mess-free, and more successful. Many early mason jars were made from transparent blue glass, which have now become collector items.

Once Mr. Mason's patent expired in 1880, a couple of brothers with the last name Ball began crafting jars in all shapes, sizes, and colors. Today mason jars are manufactured by a variety of brands with Ball, Kerr, and Atlas being some of the best known.

Various sizes of mason jars all empty

Are All Jars Mason Jars?

Not all jars are mason jars.  One of the best ways to recognize a mason jar is by the lid.  If it has the lid and band on top, it's likely a mason jar.  Some jars may say "Mason" on them, but that doesn't necessarily mean it's a "mason jar".  The best way to confirm is testing to see if a mason jar lid will fit the jar in question.

We should also note that there is a difference between a mason jar and a canning jar.  There are many jars on the market that have the standard sized opening and will fit the two part lid.  However, the glass in the jars may be unsuitable for canning because it hasn't been treated to withstand the heat needed for processing.  Jars may indicate on the bottom if it's unsafe for canning.

There are many vintage jars with unusual shapes that, nonetheless, fit the standard mason jar sized lid.  You can read more about some of these vintage mason jars HERE.

Are Mason Jars Airtight?

You can achieve a nice tight seal on a mason jar if the lid uses some kind of gasket or soft material that pushes up against the jar as the lid is tightened.  This can be done with a standard lid and band or a plastic lid with a silicone gasket. 

Mason jars can have an airtight seal if they go through the canning or pressurizing process. This process includes sterilizing the jars, adding in your canning recipe, then creating a vacuum seal by heating the jar in either a water bath canner or a pressure canner.  Correctly canning fruits and vegetables makes them shelf stable and prevents bacterial growth in the jar.  You can read more about the types of preserving methods for mason jars HERE.

Stacks of home preserves in mason jars

Are Mason Jars Heat Proof?

Mason jars are made from a specific glass material called soda-lime glass. While you can heat mason jars to 392F maximum, it requires a slow heating process. This process may include first heating the mason jars under warm and hot water before using them in a warmer environment.  

Even though mason jars have a relatively high temperature that they can withstand, they have low thermal shock resistance which means quick changes in temperature can cause them to crack or break. If you heat them too quickly, they can shatter. Mason jars with defects can also easily break.

Oven with oven door open and light on inside

Are Mason Jars Oven Safe?

It's recommended not to use mason jars in the oven because they are not made of tempered glass. Their glass material is susceptible to heating up too quickly and breaking.  The oven is also not a recommended way to process and seal jars because oven temperatures are too variable and inconsistent.  Add in the risk of breaking or shattering and you can see why ovens and mason jars don't go well together.  

Microwave with hand pressing buttons

Are Mason Jars Microwave Safe?

For the most part it's safe to put a mason jar in the microwave, but you should also be cautious.  Remember that mason jars don't do will with temperature swings, so there is always a risk that a mason jar could break in a microwave.

A quick note – the metal tops of mason jars are never microwaveable. When heating a mason jar in the microwave, remove anything that isn't glass or food before turning on your appliance.

Freezer drawer with frozen food including food in jars

Are Mason Jars Freezer Safe?

Mason jars are durable enough to withstand cold temperatures in both the fridge and freezer.  You can freeze items in mason jars, though it's best freeze food in straight jars without shoulders meaning there isn't a curve to the jar just under the mouth.  The danger is food will expand once frozen and may push against the jar and crack it. 

Another tip is to leave some space in your jars because food typically expands when it's freezing. The jars are more likely to stay intact if you leave enough room when filling them.

If you are worried about broken jars or glass in your freezer, you might also consider our silicone freezer jars which don't pose a risk of breaking if the food expands.

Open dishwasher with woman loading glass cup

Are Mason Jars Dishwasher Safe?

Yes, mason jars are dishwasher safe. When placing the mason jar in the dishwasher, remove the metal lid and wash it separately. While the metal lid is also dishwasher safe, it can easily wear down and rust due to the ingredients in detergents.  Our mason jars accessories are also dishwasher safe on the top rack, so feel free to throw them in with your jars.

Mason jars with no lid and something green in the bottom.

Using Mason Jars at Home

Now that you have all the best information on mason jars, you can use them however you please. Whether you use your mason jars to spruce up your wedding décor or to help you create the tastiest crepes (with the help of the Ergo Spout®), you'll find this jar remains timeless, for a reason!

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