Creating glass containers can be accomplished by one of two different processes – the Blow and Blow, or the Press and Blow process. Each process is chosen based on the kind of glass bottle being made. All glass bottles start out as raw materials. Silica (sand), soda ash, limestone, and cullet (furnace-ready, recycled glass) are combined into a specific mixture based on the desired properties of the bottle. The mixture is then melted at high temperatures in the furnace until it becomes a molten material, ready for formation. The type of glass this mixture will produce is known as soda-lime glass, the most popular glass for food and beverages.

Glass Forming Methods

Molten glass gobs are cut by a perfectly-timed blade to ensure each gob is of equal weight before it goes into the forming machine. The weight of a gob is important to the formation process for each glass container being made. The molded glass is created by gravity feeding gobs of molten glass into a forming machine, where pressure forms the neck and basic shape of the bottle. Once the neck finish and the general glass bottle shape has been achieved, the form is known as a parison. To achieve the final container shape, one of two processes are used.


Press and Blow Process


The Press and Blow process is the most commonly used method in glass bottle manufacturing. It uses an individual section (IS) machine, which is separated into varying sections to produce several containers of the same size simultaneously. The molten glass is cut with a shearing blade into a specific gob size. The gob falls into the machine by force of gravity. A metal plunger is used to push the gob down into the mold, where it starts to take shape and become a parison. The parison is then transferred into the blow mold and reheated so that the parison is soft enough to finish off the dimensions of the glass. Once the parison is reheated to blowing temperature, air is injected to blow the container into shape. Press and blow methods are typically used for manufacturing wide-mouth bottles and glass jars as their size allows the plunger into the parison.


Blow and Blow Process


The Blow and Blow process is used to create narrow containers. It also requires an IS machine, where gobs of molten glass are gravity fed into the mold. The parison is created by using compressed air to form the neck finish and basic bottle shape. The parison is then flipped 180 degrees and reheated before air is again injected to blow the container into its final shape. Compressed air is once again used to blow the bottle into its desired shape. Blow and Blow methods are best used for glass bottle manufacturing requiring different neck thicknesses.


Finishing the Process


Regardless of the process used, once the bottle has been completely formed, it is removed from the mold and transferred to the annealing lehr. The lehr reheats the bottes to a temperature of about 1,050 degrees Fahrenheit then gradually cools them to about 390F. This process allows the glass to cool at an even rate - eliminating internal stresses in the glass that could lead to cracking or shattering. Bottles are then subjected to careful inspections to ensure they meet quality control guidelines. Any bottles showing imperfections, including bubbles, cracks, or misshapen areas, are removed from the line and used as cullet. All remaining bottles are sorted according to size and type. The bottles are then packaged on pallets and prepared for shipping.


Keeping your freezer filled with homemade broth is a fantastic way to keep your home stocked with healthy convenience food. But after stewing and brewing all that broth, you need a simple, nontoxic way to store it.


Plastic containers can work fine in a pinch, but plastic food storage does come with some concerns about leeching chemicals. Pressure canning the broth in glass jars in another option, like a CBD flower jar, but requires more work and attention.


Filling up a glass jar and popping it in the freezer, though? Now that’s a whole lot simpler.


Simple Tips for Freezing in Glass


1. Cool Your Broth


A great place to start is to cool your broth before ladling into the jars, then completely cool the jars of broth in the fridge before freezing.


This does two things:


It won’t shock the jars when you fill them with broth (that means giving them such a huge temperature change that the glass shatters), and


You won’t burn yourself by ladling hot broth into jars and spilling on yourself. Not that such a thing could ever happen in my kitchen.


2. Fill With Less Broth Than You Think


This is a really easy mistake to make and was my biggest mistake in the past.


I used to leave 1-2 inches of headspace in the jars when filling them up with broth, thinking that there was plenty of room for it to expand while freezing. But most of them would still break and crack. I was stumped.



Turns out that it isn’t the top of the jar you need to be mindful of when filling your jars. It’s the shoulders.


Anytime you freeze in a glass jar that has shoulders, you have to make sure that the broth stays below the shoulders while it freezes and expands. That means that the broth should be 2-3 inches below the shoulders before you stick it in the freezer.


3. Use Wide Mouth Mason Jars


Instead of using regular qube jars and worrying about the shoulders, you can use wide mouth mason jars.


These wide mouth jars really are the best for freezing broth. Since they lack the shoulders that most jars have, the jar isn’t put under pressure when the broth freezes and expands. I don’t have many of these, but I do reach for them first when I go to freeze broth.


Someone even told me that they stick warm broth right in the freezer in wide mouth jars with nary a glass casualty.


4. Cap Loosely


When jars are tightly capped before freezing, they tend to break more often. If you just loosely place the lids on until the broth is totally frozen, the jars hold up better. (These lids are especially handy when storing food in jars.)


Once the broth is frozen, you can tighten the lids if you remember. It’s not a big deal if you forget, though. I rarely think to do it!


5. Leave Space Between Jars in the Freezer


For some reason, jars that are touching when placed in the freezer seem to break more readily, as well. This problem has another simple solution: just leave a little space between the jars when placing in the freezer.


There are great tips in the comments section, so give them a scan if you want more ideas! Some of my favorites:


Place your jars in a cardboard box (like the one mason concentrate jar sets are sold in) before putting in the freezer. This allows you to easily keep some distance between them and can also be handy if you use a chest freezer. Or use a JarBox, a genius product!


Slip your jars into clean socks before putting them in the freezer. This prevents them from bumping against each other and breaking that way.


Try Glasslock storage containers. The glass is tempered, so it’s stronger and better able to handle temperature changes. They are pricier than canning or repurposed weed jars, but might be an investment you’d like to make since you can also cook with them.


Stick with jars that are designated as freezer-safe, like these pint-and-a-half wide mouth jars, or use smaller size jars like wide mouth pint, half-pint, and 4-ounce.