How Enamel Rater Testing Confirms Liner Consistency

Metal Enamel Rating Diagram

Traditional can liners, such as BPANI or epoxy, were developed for beverages such as soft drinks and light beer and generally work well for those liquids. But what about harder-to-hold beverages like wine, cider, ready-to-drink (RTD) cocktails, hydration beverages, or cannabevs?

Many of these products feature high alcohol content, acidic ingredients (low pH), sulfites, and/or contain elevated levels of sodium chloride.

While these types of beverages are exploding in popularity, many companies developing the products may not realize the risk they are taking by not conducting product-to-package compatibility tests and exploring all available liner options.

Product compatibility testing is essential because a small failure in even one can on a pallet of 5,000+ could cause enough damage that the entire pallet of product would have to be scrapped. It could even potentially ruin a whole run or batch depending on the rate of occurrence and storage conditions. We’ve seen it happen and it’s a devastating loss for a company. Large-scale failures like these aren’t often discussed in our industry, but they happen more often than many realize.

So what can a beverage maker do if they have a harder-to-hold drink to avoid this potential catastrophe?

The aTULC can liner is proven to be the best option for holding these liquids.

How do we know that aTULC is the more reliable option for harder-to-hold beverages versus other common can liners?

The can industry uses enamel rating testing to verify the integrity of a can lining post-production. Results from the enamel rater help indicate whether a can lining is applied consistently, and as a result, is more or less prone to fail if exposed to corrosive materials over time.

In this article, we’ll dive into the enamel rater testing, how aTULC has been determined to be the most reliable can lining for harder-to-hold beverages, and how choosing the best can liner for your brand can impact your overall success.

How is the Enamel Rater Test conducted?

The enamel rater test is performed by filling a can with a conductive electrolyte, like salty water, and then placing an electronic gauge into the liquid. A positive voltage is then applied from the outside to the metal wall of the can. The liquid inside the can and the metal wall are both able to conduct electricity, however the inner lining should not conduct electricity. If the lining is applied properly and without any inconsistencies, then no electrical current will be detected by the gauge. The lining will have formed a solid barrier between the two conductors.

Essentially, during the test, if the gauge inside the liquid registers an electrical current, then the lining of the can is compromised in some way.


However, detecting a current doesn’t mean that a liner has completely failed. There are industry standards that determine whether the current observed is acceptable. The measurement for this test is in milliamps (mA). A measurement of 5mA or below is widely considered “good”. So, if a can registers 5mA or less then it is not likely to fail under normal circumstances with most beverages.

The enamel rater test is one of three different quality checks that American Canning conducts on their aTULC manufacturing line. Of the three QC checkpoints, this test is the one that clearly shows the importance of a consistent and quality lining inside an aluminum can. Can failure is a serious problem that is often caused by secondary corrosion. But before we dive into the results of the test, let’s define exactly what we mean when we’re talking about can failure.

What is can failure?

The easiest way to think about a failed can is this: a failed can is a leaky can. You assume when you put your liquid product in the can that it will stay in that can until a customer cracks it open and begins enjoying it. It should be able to sit on a pallet without leaking for an extended period of time.

However, sometimes the product inside a can comes into direct contact with the aluminum wall of the can, either because the liquid ate away at the inner lining or because the inner lining had inconsistencies that allowed for the liquid to directly contact the wall. If this liquid then corrodes the aluminum enough that a leak forms, that can has completely failed.

aTULC Compared to EPOXY & BPANI

One failed can on a pallet of 5,000+ doesn’t sound so bad. However, that’s not usually where the problems stop. If the contents of a can leak out onto the outside of other cans, you get secondary corrosion because most can liners are only on the inside of a can (aTULC lining is on both the inside and outside). 

With no outer liner, there’s nothing to stop corrosion from happening on the outside of an aluminum can and then your one leaky can becomes such a problem that the entire pallet of product is destroyed, often within days or weeks. 

This is why we take can failure so seriously at American Canning. It’s not enough that a vast majority of your cans will hold your beverage just fine. The standards must be extremely high to protect your business potentially catastrophic loss. 

Results of aTULC and other common liners

We tested our aTULC liner alongside other manufactures and liner types to determine which of these linings is most consistent and better able to protect the integrity of the aluminum can from liquids that are more likely to cause corrosion such as wine, cider, spirits, highly acidic drinks, and hydration (high-salt) beverages. This test was a random sampling and used common, commercially available can liners from multiple manufacturers to ensure that the results were fair.

As you can see in the chart below, aTULC-lined cans rarely registered a current during the testing.

Metal Enamel Rating Results

In fact, the highest amount measured in any aTULC can was 0.38 mA, well below the industry standard of 5mA that is considered “good.” We put that word in quotes because American Canning holds aTULC to an even higher standard. If an aTULC can registered above 1mA we would consider the liner compromised. In all of our studies, we didn’t see anywhere close to this.

As laid out above, when discussing the devastating consequences of can failure, there’s a reason we have such a high standard for aTULC. When you consider the price point of premium beverages, brands are at risk for huge money loss if they don’t invest in a can that protects their products.

Other liners generally performed well in our testing, with only a few cans that surpassed the industry standard of 5mA. These linings are worth considering for more traditional canned beverages such as light beers and soft drinks, as those drinks pose far less risk to can integrity.

However, it’s worth noting just how much deviation exists in these liners. As you can see, though they performed well, each of the other liners had outliers that exceeded the industry standard of 5mA. Some can linings were so inconsistent that they registered currents well into the double digits.

This shows that though most of the cans on a pallet will be lined consistently, there are a few that might be significantly compromised. This isn’t a risk you can take with a harder-to-hold beverage because again, one can has the potential to create cascading failures.

What is aTULC and how is it different?

Why does aTULC perform so much better than other liners in the enamel rating test? It’s all down to the material of the can liner and how its applied to the aluminum cans. As you can see in the video below, aTULC isn’t applied like traditional can liners.

Most can linings are applied via high-speed sprayers that jet material into the can during production. For the most part, this is a highly effective and efficient way to apply a can liner. However, because spraying by nature is inconsistent, there’s always potential for small spots or areas that don’t get properly coated with the liner.

Spray On Liner

The electric current shows up in the liquid during the enamel rating test because there are micro-fissures within the liner that allow the aluminum can to come into direct contact with the internal contents. Because of this, a hard-to-hold beverage might begin to eat away at the aluminum wall of the can and over time will cause corrosion and can failure. Again, not every time, not even a vast majority of times, but it only takes one failed can to ruin an entire pallet or production run.

The aTULC liner is applied to the can in a completely different way. Instead of a spray, the liner is rolled onto the aluminum sheet prior to production. It’s a double-layered liner applied to both sides of the aluminum sheet. This way, when the cans are formed from the aluminum, every part of the surface area is covered in the aTULC liner.

Pre-coated Aluminum Sheet 

Is aTULC new? Yes and no.

aTULC has been used in Japan for more than 20 years by Toyo Seikan Group Holdings Ltd. Thus, aTULC stands for “aluminum Toyo Ultimate Can.” But, aTULC is new to the United States market and American Canning is the only can manufacturer in the entire Western Hemisphere with a license to produce aTULC cans.

How to know if aTULC is right for your product

If you are producing a beverage that would fall into the hard-to-hold category such as ready-to-drink cocktails, wine, cannabis drinks, or anything with high salinity or other potentially corrosive ingredients, you will need to do significant research into the cans you’re using to hold these products.

American Canning’s aTULC can lining is the smart (and most sustainable) choice for these types of beverages. As a manufacturer of aTULC cans and official distributor for Ball Corporation, our sales team is well equipped to discuss best-fit cans for your brand. 

Or, if you’d like to take a look at the product yourself and conduct testing, you can have an aTULC sampler pack shipped to you, just pay the cost of shipping.

For more information on aTULC can manufacturing, visit