Aluminum is widely used for beverage cans due to its light weight, malleability, good corrosion resistance, and because it can be endlessly recycled and is safer than glass in festive or sports settings.
Its corrosion resistance relies notably on the presence of an internal coating and the spontaneous formation of a thin layer of aluminum oxide (Al₂O₃) on the metal surface.
However, under certain conditions, these barriers may be weakened, leading to corrosion phenomena that can ultimately perforate the cans. The presence of sugar, which can complex with aluminum ions, then becomes a major aggravating factor.
This article presents the corrosion mechanisms involved and provides practical guidance to reduce technical and financial risks related to formulation–packaging incompatibility in aluminum.

1. The role of the internal coating

To prevent corrosion, cans are generally coated internally with a protective film (often an organic lacquer). However:

• This coating may degrade over time under the effect of aggressive formulations.
• It may also present microscopic defects (bubbles, microcracks, poor adhesion), locally exposing the aluminum.
• Certain substances, such as sugars or acids, may interact with the coating and alter its barrier properties.

2. Aggravating factors

Several factors related to the formulation of beverages can explain premature corrosion of aluminum:

• Acidic pH: most beverages (soft drinks, juices, energy drinks, cocktails, etc.) have an acidic pH (often between 2.5 and 4). Below a certain threshold (pH ≲ 4), the natural oxide layer, when in contact with the liquid, can partially dissolve, making the metal more vulnerable.
• High sugar content: sugars (such as sucrose, glucose, or fructose) can form complexes with aluminum ions released at the surface. This prevents the re-formation of the protective oxide layer, promoting continuous corrosion.
• Presence of alcohol: ethanol can alter the protective lacquer, especially in the presence of acids and sugars. It also changes the polarity of the mixture, affecting the solubility of ions and the stability of the oxide film. The combination of alcohol + sugar + acidity creates a particularly aggressive environment for aluminum.
• Increased conductivity: solutions rich in sugar (and/or organic acids) exhibit higher electrical conductivity. This facilitates ion and electron exchange at the metal surface, accelerating electrochemical corrosion reactions.

3. A mechanism similar to an electrochemical cell

The corrosion mechanism can be compared to what happens in a battery:

• Aluminum acts as the anode: it oxidizes, releasing electrons (Al → Al³⁺ + 3e⁻).
• The beverage liquid (mixture of water, acids, alcohol, sugar, etc.) acts as an electrolyte.
• Micro-heterogeneities containing impurities, either in the metal or in the internal coating, can act as reduction catalysts and create local electrochemical cells: small anodic and cathodic zones where oxidation/reduction reactions occur.

Result: a local electrical current is created, accelerating aluminum oxidation. Corrosion develops in a localized manner, often as pits, which can eventually compromise the integrity of the can.

4. Potential consequences of corrosion

• Product alteration: metal ions released by corrosion may interact with the beverage and cause flavor changes or color instability.
• Can perforation: if corrosion progresses through the wall, it can cause leakage.

Example of corrosion resulting in perforation of an aluminum can

5. How to guard against these risks

These phenomena are often subtle at first—how can they be anticipated?

A few tests and inspections on cans from different suppliers will allow you to eliminate high-risk lots:uelques tests et observations sur les canettes vont vous permettre d’éliminer les lots à risque :

1Open and examine 2 or 3 cans from each lot by cutting them open and observing the internal coating, if necessary under magnification.

2Test the compatibility of the beverage with the can material by performing accelerated aging tests (protocol suggestion in the attached annex).

3After these tests, observe any alteration of the internal coating and any change in the organoleptic properties or color of the product.

🔴 If no defect has been detected and to fully exclude the risk, it is still advisable to:

• Conduct triangular tasting tests (as described in the blog article “Good Tasting Practices for Spirits from Fermented Products”), with several trained tasters.
• Measure dissolved aluminum and compare it with a control beverage stored in a glass bottle.

ANNEX : Example of standard protocol for an accelerated aging test on aluminum cans

Samples

• 4 to 6 filled cans per batch or supplier.
• Keep at least 2 filled cans per batch or supplier at room temperature for comparison.
• Preserve the reference beverage in 4 glass bottles (screw cap with bakelite seal), at least 200 mL each, stored at room temperature and protected from light.

Accelerated standard conditions

• Temperature: 40 ± 2 °C
• Duration: 4 to 6 weeks (approximately equivalent to 6 to 12 months at room temperature).
• Position: store cans upright and lying down (to test prolonged contact of the liquid with the seam and the lid).
• Optional: a second set stored at 50 °C for 2 weeks to simulate extreme thermal stress.

Monitoring

Weekly: external visual inspection of all cans for swelling, leakage, or deformation.

After 4 weeks: open and examine one can internally:

• Collect the liquid.
• Cut the can open.
• Compare the internal wall with that of a reference can.
• Look for: dark spots, pitting, loss of gloss, or delamination of the coating.

Analytical measurements on the liquid

• pH (possible variation linked to corrosion).
• Sensory evaluation: metallic taste, color change, deposits — compared to the reference beverage.

Interpretation

• No visible corrosion and stable taste/color → compatible can–beverage pairing.
• Coating delamination or pH change (> 0.3 units) → likely chemical interaction.
• Presence of pits, dark zones, or high dissolved aluminum (>0.5 mg/L) → incompatibility between the can and the formulation.

🔴 If after 4 weeks no deterioration is observed (neither on the can nor on the beverage), continue the accelerated test for at least 2 more weeks on the remaining cans and repeat inspections and analytical measurements at the end of the test.