The Purpose of Beer Bottle Bumps

March 26, 2010 at 12:01 am 8 comments

Many people have noticed the small bumps on the side of beer bottles, near the base (the “heel”). They’re not just on beer bottles either, every glass bottle in my house has them, which are mostly beer bottles.

These are typically called “mold codes” or “heel codes” and there are many different ideas about what these are for, but I could only confirm one.

It is a popular notion that these bumps help the bottler know how many times the bottle has been reused. I couldn’t find any proof that they are used for this. In fact, I’m not sure how these dots would convey that information since they are made when the bottle is molded.

This rumor seems to confuse the heel code with bottle date codes, which are traditionally found on the neck of the bottle. On newer bottles, date codes are stamped with ink. On older bottles, they were part of the glass mold and were often beside an embossed logo from the glass producer or bottler. Dating on older bottles helped bottlers know how long they had been in circulation.

I have read that heel codes are read by production equipment so the machines know how large the bottle is for proper filling and shipping. I could not find any concrete proof of this, but considering the next point, it’s certainly possible.

There are machines that measure many different bottle attributes to determine the quality of the bottle. If a bottle does not meet the quality standards, an associated machine will read the heel code from bottle. This makes a lot of sense because the bumps actually refer to the mold that made the bottle. So, if there is a quality problem with that bottle, the mold can be inspected for damage or wear.


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Written By: Chad Upton

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Sources: Emhart Glass, Society for Historical Archeology (PDF), Glass Factory Marks

Entry filed under: Around The House, Demystified. Tags: , , , , , , , , , , , , .

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8 Comments Add your own

  • 1. carolyn  |  June 24, 2012 at 7:47 pm

    Each time the bottle is returned it is sanitized and refilled. At this time they knock off one bump. When the bottle gets to the last bump it is taken out of circulation and recycled.

  • 2. Richard  |  July 21, 2012 at 10:56 am

    I spent 18 years in the glass bottle and jar industry. The comment about knocking off one of the bumps is not true. In fact, it would damage the bottle’s integrity, and cause a very weak spot, making it unsuitable for refilling. All of the markings on glass containers are for identification purposes. They tell us where, when, and in which mold a container was made, enabling us to take out of production any molds that are making imperfect bottles. Imperfections include such things as thin walls in one area, finishes (tops, not smoothness of surfaces) that do not allow for a perfect seal, and so on. Also, most bottles and jars are not sanitized and refilled, as Carolyn said. They are crushed into what is called cullet. Cullet is the largest ingredient in making glass, followed by sand, and then whatever chemicals are needed for the particular glass that is being made. The sanitizing and refilling might apply to certain companies that take back only their own bottles, and refill them. However, I think they have found that it’s easier and less expensive to use new bottles.


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  • 4. Jim  |  March 30, 2016 at 1:50 pm

    Hmm, thought the bumps were for anneaking reasons, less surface area out of the glass ovens…

  • 5. James  |  July 6, 2016 at 4:08 pm

    Richard is correct all mold markings are for identification purposes. The dots specifically relate to the identification of the mold from which the bottle was produced. Glass forming machines can run as few as 8 single sections or 10 quad sections. If a defect is discovered in the bottle, code readers can identify the specific mold that is affected and remove it from the bottle stream without affecting the good bottles. The defective bottles are then crushed into cullet and eventually added back into the “batch”

  • 6. Thomas  |  December 29, 2016 at 7:07 pm

    but doesn’t explain dot sequences on neck & shoulders. Could they just be molding aides, like release ports or grasping aid?

  • 7. Christopher Reiff  |  July 8, 2017 at 3:59 pm

    The dot pattern on the heel of beer bottles and wine bottles are for all sorts of information pertaining to the manufacturer, size of bottle, date of production, mold number, pressure specs that bottle can be taken before failure. On most product fill lines there are machines made by AGR Intl – American Glass International Inc, located in Butler, Pa or by a another company know as Powers Check systems that manufacture equipment to inspect bottles before they are filled in order to prevent wasted product and defects in bottles such cracked bottles, large volume difference from bottle to bottle, and “Bird Whips”! Bird Whips are arcs of glass from one side of the bottle to the other side that could potentially break off when the bottle is filled and contaminate the product and passing glass to the customer!
    Another bump code you may see on bottles is on the bottom of the bottle and would look like little peanut shapes in the form of a circle! This would also be scanned by certain companies!

  • 8. Pamela Grubb  |  September 18, 2022 at 3:47 pm

    There are small dots around the neck of coors light bottles I wonder if that is more of something to do if people are blind it would help them know exactly what they in their hands. Could it possibly be something in Braille ?


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