The Engineering Behind the Modern Glass Bottle

Chances are you've used a glass bottle just today – you could even be sipping out of one right now. While the modern glass bottle may seem boring and rather simple, they actually represent centuries of innovation in manufacturing and production. 

Adding to that, there are some simple questions about glass bottles that you likely don't have an answer to... Like, why are they shaped like they are? Why do they have those little bumps on the bottom? Why are they different colors? In order to answer these questions, we have to understand how they're made.

Glass bottles start their lives as a collection of various raw materials, mainly comprised of silica sand, soda ash, and limestone. Silica sand makes up the largest percentage of about 40%, soda ash makes up 15% and helps the silica melt evenly, and the limestone, usually making up about 10% of the material helps with durability. As for the other 35% of the material – it's usually a mixture of other compounds and recycled glass.

Recycled glass melts at a lower temperature than the raw materials, so for every 10% of recycled glass in the mix, 2.5% less energy is used in manufacturing the bottles.

If manufacturers want to make brown or amber glass like beer bottles, a mixture of iron, sulfur and carbon is added. To produce green glass, a chrome oxide is added to the material. Tinting the glass these colors protects the beverage inside from ultraviolet light and radiation, which could affect flavor and perishability in clear glass bottles.

While it may not seem like it, in most cases, making glass packaging requires much less energy than metal and plastic alternatives. Along with the abundance of glass's raw materials, the end product is one of the most eco-friendly on the planet.

All the raw materials are mixed together and melted in a furnace at 2730 degrees Fahrenheit over the course of a day. This lengthy amount time ensures a homogenous mixture.

The liquid glass is then poured out of the furnace and portioned out relative to the type glass bottle being made. Molten glass is then pushed into a mold and then blown with air, usually through a machine. This transforms the glass from the molten raw material into a near-final product that only needs to cool.

As for cooling, this is carefully controlled through a process called annealing, which ensure homogenous material strength and that the bottles don't have any thermal shock from differential cooling.

That's essentially how the common glass bottle is made, but they contain a series of quirks that give light to their deeper engineering.

Around the base of most glass bottles, there's a series of bumps on the side. On older bottles, manufacturers would use the bumps as date codes, allowing them to see how long a bottle was in circulation. While this is still used some in modern manufacturing, they are generally used as mold markers, so if there are defects, the manufacturer can trace the source of the problem. 

As for why glass bottles have the shape that they do, that all comes down to packaging constraints. Long-necked bottles have been used for a little over 100 years now. This design allows packers to easily seal off the top with a small bottle cap, reducing the size of the seal and thus saving money. A smaller seal on a beverage container also is stronger than one spread across a larger area.

Some beer bottle necks will be more bulbous than others, which is used to collect particles that could be in the beer when poured.

[see-also]

Long-necked bottles that are round also allow for a fairly efficient means of packaging while also decreasing the probability of breakage in transport.

All of these general characteristics, from manufacturing to packaging, shape why glass bottles look like they do today. Differing designs are usually created to add extra style to a product or to reduce the amount of raw material and cut down on cost. For the most part, the current design of glass bottles has remained constant for many years now, but the industry is always looking to innovate, so the bottles of the future might just look a little different.