Tamper Evident

Why there’s a giant button in the middle of your salsa jar, and why baby food jars had it first.

By Ernie Smith

Today in Tedium: As we pointed out in our recent piece on beverage cans, a lot of innovation had to get into place to get us to the point where we are today, where you can open a can with another can, as a TikTok user so helpfully showed us. And one of the points of innovation we didn’t even bring up is that the pop-top lid is brilliant because it’s obvious it hasn’t been tampered with. Problem is, that design doesn’t work for every product sold in stores. Some jars need to be built to be reusable, but they also need to be re-opened. Today’s Tedium is going to talk about one of the most common things in your refrigerator that you never think about—the tamper-evident “safety button” that you commonly see on the lids of jars. Where did it come from, and why didn’t know you needed an article about it until now? — Ernie @ Tedium

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The year that the Mason jar was first developed by John Landis Mason. The invention, which relies on a glass jar with a lid that has a prominent screw thread and a vacuum seal, became highly genericized in the nearly two centuries since the tinsmith developed the jar and lid setup. It gained prominence in the 21st century as a hipster icon, because every object of nostalgia needs a moment in the sun.


Ernie Smith, a man with a salsa problem. (Tai’s Captures/Unsplash)

What made me think of writing about this extremely specific topic?

I don’t feel like I always need to explain myself, but this time, I do. My name is Ernie Smith, and I have a problem. I’m an enthusiast of chips and salsa. The combination, while fairly basic, is truly special.

The chips are a vessel with which the salsa is served. And the salsa highlights my tendency towards tomato-based foods. Salsa can be had fresh, but usually, I tend to prefer the vacuum-sealed kind, which has a different character from the fresh stuff. Something about being a shelf-stable good makes it a good, basic snack.

I wouldn’t go so far as to describe salsa as a vegetable, as the USDA once did, but I will say that it is a consistent, tasty snack that I am personally responsible for consuming more than my fair share of.

As a result of this, I see a lot of vacuum-sealed lids. Usually green or black or yellow, they have a very consistent design to them, reflecting the need for vacuum sealing.

A key feature of the lids, though, is a bump in the middle. The bump only makes itself known when the can is open. Before that point, it is basically flattened, kind of like a suction cup, reacting to the lack of air between the top of the container and the food contained inside.


Is there a topic more tedious than lids? Someone tell me. (Rob Wicks/Unsplash)

On some jars, it is heavily emphasized through design as an important safety feature. On others, it is just kind of there, never drawing attention to itself in any way.

So I see a lot of these buttons. And while I won’t go so far as to say I think about them a lot, I am curious about them.

But here’s something interesting I noticed when I started trying to dig into this. There were lots of people who were writing about aluminum beverage cans, one of the most important kinds of cans that exist. But the safety buttons on glass jars? Not really. It might as well have been an unknown quantity.

(There were much more curious about how to easily open them, to which I say: Easy, put a butter knife under one of the edges of the jar, then pull up. It will let in just enough air to make the jar a breeze to open.)

So where did this design come from? It took a little bit of digging on my end, but there is a decent thread here, a story of a quality-control technology that proved to be just as important outside the factory. The object’s name has changed a number of times over the years, with its best-known nomenclature being the “safety button.”

To explain how the safety button came about, we have to talk about baby food jars. Yes, baby food jars.


The year that an inventor named Carl Schoonmaker filed for a patent for a “telltale closure device” intended for home canners, “whereby a person upon completion of the canning process may positively know whether the contents of the container have been properly sealed.” When fully sucked in, a large dome is created with the lid style, which makes it clear that the vacuum sealing process has been successful. While not anywhere near what we have today, in many ways, this style eventually led to the modern day “safety button” lid.

Baby Food

Baby food jars are going to make a Mason Jar-style comeback, mark my words. (via eBay)

The role that baby food jars play in the pop-top lid, a.k.a. the “safety button”

Baby food jars are particularly important to the discussion of vacuum-sealed cans and safety. They are the earliest foods many babies consume, and the product inside is designed to be consumed, obviously, by those with still-growing immune systems.

Getting baby food right is extremely important for the food industry, because it is something that can cause many problems when done wrong. And if you can’t get baby food right, kids may decide not to buy other kinds of foods from you later on.

And in the 1960s, concerns were rising about baby food, which was being sold to consumers in glass jars for the first time around this period. This was an important industry that the food industry took steps to get right for the positive PR goodwill that it could engender, as the 2014 Amy Bentley book Inventing Baby Food explained:

As an essential product laden with strong, positive cultural meaning, by the 1960s baby food was an established, pervasive presence in American culture as a whole. Every week across the country there appeared in the women’s pages of newspapers and magazines recipes listing commercial baby food as an ingredient: a glaze for Easter ham using baby food apricots, an easy dessert made with baby food prunes, or a parfait featuring baby food peaches. The recipes were developed by baby food manufacturers and supplied to overworked female journalists, grateful for material they could include in their weekly home and entertainment sections. Further, the little glass baby food jars that by the 1960s were used by all commercial baby food manufacturers proved to be the perfect shape and size for multiple uses.

Early advertising for these jars, which were created almost as a marketing strategy, emphasized the value of being able to see the food that you were being sold.

And the industry worked hard to get it right. The company Owens-Illinois, now known as O-I, developed a type of glass lid style specifically for baby food jars called Vapak, which it patented in the late 1950s and later began to sell for non-baby-food products. As the patent filing for the “hermetically sealed food package with tamper resistant closure” explained:

It is most important that food containers remain hermetically sealed from the time of filling and closing under sterile conditions until they reach the ultimate consumer who is about to or is going to use the contents. Otherwise, as is readily understood, sterility and suitability of the food, etc., for human consumption cannot be assured. This is particularly important and critical in the field of baby foods.

Of course, they could only do so much about consumers. One common situation reported within the Canadian media in particular was the rise of people who would open up baby food jars on shelves, try a little of the food, then put it back. The jars looked so attractive, right?

This was a cause for concern, and one that the Canadian Association of Consumers had called out prominently in the press.

Baby Food Lid

It may not look like much, but that little dimple on the lid is one of the first examples of a “safety button” on a food jar. (The Spokesman-Review/Newspapers.com)

The food industry was already working on this, creating designs that signified safety and sharing them industry-wide. One such design was called the “pop-top lid,” which the industry developed in response to consumer complaints in the 1960s. Per my research, this design appeared to hit sometime around 1963—Heinz, a prominent maker of baby food during the era, was not promoting it in 1962 ads, but a 1963 ad from Gerber included an image of its “quick-twist” lid that did clearly show the pop-up button, and a 1963 story in the Fort Lauderdale News painted the lids as a new feature.

This lid is the predecessor to the modern safety-button design we see on a lot of lids today. And while good, it wasn’t perfect. After all, it couldn’t prevent people from randomly opening jars in supermarkets, though it could help offer a signifier to consumers that what they were opening was actually safe.

Even with lots of work put into improving these lids, complaints still frequently emerge. Gerber, notably, faced numerous controversies in the 1980s over glass shards discovered in its baby food, which led to an aggressive PR response that focused heavily on the pop-top lids—and also led the company to improve its packaging standards over time.

In many ways, this push to improve packaging standards in the 1980s led to the safety button becoming more common on products throughout the grocery aisle.

“Plan to can every extra vegetable from your Victory garden and don’t worry if your dealer hasn’t jars with the kinds of caps you have been accustomed to using.”

— A statement from a syndicated 1943 article, titled “Glass Jars for Victory Canning,” encouraging people to can using different types of lids that they’re not used to, in part because the wartime need for raw goods had depleted the supply of more traditional options.

Safety Button Patent

Continental White Cap’s key safety-button patent, which gave us the modern design for this vacuum-seal check. It wasn’t first, but it was the modern form. (Google Patents)

How pressure-indicating lids found their way into the rest of the supermarket

Baby food may have been the impetus for safety lids, but the fact of the matter is, it was a noble goal for pretty much any kind of food that relied on vacuum-sealing for safe-keeping. It was worth getting right.

Starting in the 1950s, supermarkets were becoming more common and pre-sealed cans were a key element of their popularity. Companies like OI Glass developed processes to both vacuum seal jars at scale and confirm in the factory that the vacuum sealing had taken effect. A number of other devices appeared to offer visual indicators of the vacuum-sealing process, offering improvements on Carl Schoonmaker’s well-considered but impractical design for Mason jars.

These designs, while effective at sealing the containers, were less perfect at being visually obvious that they had been unsealed previously. You could certainly hear the pop when you opened a jam jar, but the pop only went so far.

Then a device credited to the 3M corporation in the 1970s for something called a “pressure change indicator,” which included an additional part on the lid to offer a visual indicator that the vacuum had been unsealed. This was intentional on the part of inventor Wendell J. Manske, as the patent filing states:

A problem with all of these prior art devices is that the indication provided by the flexible panel or the like is not sufficiently dramatic to warn an unsophisticated user that the contents of the container may be unsanitary. For example, the clicking or popping sound may not be heard above a high level of background noise, or the user may forget whether or not he has heard the sound. Even more serious, the user may not be aware that the lack of a click or pop indicates that the contents of the container may be subject to contamination or spoilage. The visual indication provided by the prior art closures is perhaps even less dramatic than the aforementioned sound indication. Typically, the center of a prior art closure travels about 40 mils (about 1 mm) when pressure is restored in the container. This small amount of travel, changing the center of the lid from a slightly concave surface to a slightly convex surface, may easily be overlooked. In view of the importance of the loss of vacuum within the container, a more dramatic means for warning of the possibility of unsanitary spoilage is needed.

But it, too, was imperfect. This design, while offering many of the practical cues of the modern pop-top lid, hadn’t quite nailed down the key element of the modern lid: the one-part, pop-able, fidgety nature of the safety button. Sure, it offered a clear visual cue, but it also added another part that was in danger of becoming lost or a source of littering—which, as our piece on beverage cans highlighted, created a fresh risk of safety hazard. It was a safety tool that could presumably create a fresh safety risk.

Based on my research, the company that truly modernized the design of the safety-button jar is a bit unsung. It’s a firm called Continental White Cap, and it specialized in creating jar designs for companies throughout the supermarket aisle in the 1980s and 1990s. The direct descendant of White Cap, a firm that developed early lid designs starting in the 1920s, it became a prominent player in lid production that many major food manufacturers used. (It also, notably, developed the twist-off cap in the late 1950s, just in time to ride the PR wave of Chubby Checker’s “The Twist.”)

But by the 1990s, Continental White Cap found itself improving a design that everyone has seen, but nobody really talks about because it generally works quite well.

In a 1990 profile of the firm’s Pennsylvania factory, the company noted that it often developed custom lids for the many companies that relied on the firm, and had a rigorous lid-testing process.

“We have machinery that checks the steel for thickness, flexibility, pinholes and the discoloration of the steel,” manager Dan Dowling told the Hazelton, Pennsylvania Standard-Speaker. “In the printing operation, the operators measure how thick the coatings are throughout the process. Operators also measure all physical dimensions of the cap. All of that work takes one hour out of the average eight-hour shift.”

It did not just produce lids—it improved the technology behind them, filing some key patents for tamper-evident enclosures starting in the early 1990s. Their design for a tamper evident closure, developed in response to high-profile incidents in which the containers were tampered with (most infamously, the Tylenol incident, but also a high-profile blackmail scare in the U.K. involving Heinz baby food products) seal was re-applied to mask the fact that the lid had been tampered with, the Continental White Cap design is described as a “high energy button,” with the intention that the vacuum seal would be harder to produce in the future. From the filing:

However, because of a number of reported incidents of food and drug package tampering, more is required than merely a closure with a button which has “up” and “down” positions. Consideration has been given to providing the button with systems which not only clearly indicate that the closure has been removed from an associated container, but also wherein the system cannot be readily defeated by again producing a vacuum within the container after the closure has been reapplied.

It, however, has been found that in order to provide an irreversible tamper indicating system for a closure provided with a vacuum actuated button, a greater flipping action of the button is required to operate the tamper indicating system and therefore a closure having a high energy button has become necessary.

The company also developed a system involving microcapsules that would slightly discolor the lid of a jar to reflect that it had already been opened.

We live in a better world because of the hard work that companies like Continental White Cap put in to make simple things a little more obvious. It’s important; it keeps our food safe; and it’s completely unsung.

The nice thing about vacuum-sealed lids and safety buttons of this nature is that it’s generally easy to detect when one has been opened for consumption. The downside, though, is that these lids can be extremely hard to open.

I mentioned the knife trick above, but that’s quite often a trick of last resort. A piece of rubber also does the trick by adding some of the missing grip that many lids do not have.

Efforts to improve lids so that they’re easier to open emerge from time to time. Each faces the natural consideration: We don’t want this thing to be easy to open in the store, so randos won’t start pulling pickles out of random containers or tampering with baby food, and we don’t want it to be easy for young kids to open, either. One of the more recent efforts is created by a company called Consumer Convenience Technologies, which has developed a new lid design called Eeasy.

This lid relies on a multi-step process. Rather than waiting for the button to pop up, you press down on it, which eases the vacuum seal, making it so that the most annoying part of opening up a lid is handled before you actually open it. This is presumably a lifesaver for people with motor skills.

Of course, it won’t work for everything—after all, these lids are designed to be somewhat difficult to open the first time for a reason, because they are designed to prevent tampering—but it could make relying on the strong-armed relative with a magic touch a thing of the past, which may in fact be a good thing.

Perhaps it could get me one step closer to enjoying my chips and salsa someday.


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Ernie Smith

Your time was just wasted by Ernie Smith

Ernie Smith is the editor of Tedium, and an active internet snarker. Between his many internet side projects, he finds time to hang out with his wife Cat, who's funnier than he is.

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