Causes And Solutions For Rusting Beer Bottle Caps

You may have encountered this before: the beer bottle caps you bought were rusty. So what are the reasons? The reasons for rusting beer bottle caps are as follows:

 

Beer bottle caps are mainly made of 0.25mm thick tin-plated or chrome-plated thin steel plates. With increasing market competition, another function of bottle caps-branding (colored caps)-is becoming increasingly prominent, placing higher demands on the printing and use of bottle caps. Sometimes, rusting of bottle caps can negatively impact the brand image of the beer. The mechanism of rusting is that after the anti-rust layer is damaged, the exposed iron reacts with water and oxygen in an electrochemical reaction, forming rust. The degree of corrosion is closely related to the bottle cap material, the anti-rust coating process, and the surrounding environment.

 

1. The Influence of Baking Temperature or Time

Excessive baking time will make the varnish or paint applied to the iron plate brittle; insufficient baking time will result in incomplete curing of the varnish or paint applied to the iron plate.

2. Insufficient Coating Amount

After the bottle caps are stamped from the pre-printed iron plate, untreated iron is exposed at the edges. These exposed areas are prone to rusting in high-humidity environments.

3. Non-perpendicularity or asymmetry of the capping star wheel leads to rust spots.

4. Collisions between bottle caps during handling and logistics cause rust spots.

5. Internal wear of the capping die and excessively low capping punch height both exacerbate wear on the bottle caps.

6. Bottle caps with water that have been coated with aluminum foil or immediately packed (in plastic packaging) do not easily evaporate moisture, accelerating the rusting process.

7. Bottle bursting during pasteurization lowers the pH of the water, further accelerating cap rusting.

 

Based on the above reasons, the following aspects should be emphasized:

1. Strengthen the appearance and corrosion resistance testing of beer bottle caps before they enter the factory.

2. During the testing process, especially when changing suppliers, strictly strengthen the testing of internal corrosion of beer bottle caps after pasteurization. 3. Strictly implement bottle cap indentation inspection; the packaging workshop should regularly check capping quality.

4. Strengthen the inspection of the capping star wheel and capping die on the filling machine; clean up promptly after crushed bottles.

5. Manufacturers can blow away residual moisture on the bottle cap before inkjet printing. This ensures inkjet printing quality (printing on the bottle cap) and also plays a positive role in preventing rust on the beer bottle cap.

Furthermore, chrome-plated iron has stronger rust resistance than galvanized iron.

 

The main functions of beer bottle caps are: first, to provide a certain degree of sealing, ensuring that CO2 inside the bottle does not leak and that external oxygen does not seep in, maintaining the freshness of the beer; second, the gasket material is non-toxic, safe, and hygienic, and will not affect the flavor of the beer, maintaining its taste; third, the high-quality printing of the label on the bottle cap plays an important role in the beer brand, advertising, and product maintenance; and fourth, when using bottle caps in breweries, the caps are suitable for high-speed filling machines, ensuring smooth cap filling and reducing cap and beer loss. Currently, the standards for judging the quality of beer bottle caps should be as follows:

 

I. Sealing Performance:

Instantaneous Pressure: Instantaneous pressure ≥ 10 kg/cm²;

Chronic Leakage: Chronic leakage rate ≤ 3.5% according to standard testing.

 

II. Gasket Odor:

Safe, hygienic, and non-toxic. A flavor test of the gasket is performed; boiling in pure water should produce no off-odor, indicating it is合格 (qualified). Furthermore, after use, the gasket's odor should not migrate into the beer, causing any impact on the beer's flavor.

 

III. Bottle Cap Characteristics

1. Paint film loss value: High-quality products require ≤ 16 mg; tin-plated iron bottle caps and chrome-plated iron bottle caps with full-color printing require ≤ 20 mg of paint film loss.

2. Corrosion resistance: In addition to meeting the copper sulfate test requirement of no obvious rust spots, the cap must also exhibit delayed rusting during normal use.

 

IV. Bottle Cap Appearance

1. The trademark text is correct, the pattern is clear, the color difference is small, and the color is stable between batches;

2. The pattern is centered, with a center-to-center deviation of ≤0.8mm;

3. The bottle cap must be free of burrs, defects, and cracks;

4. The bottle cap gasket is intact, without defects, foreign matter, or oil stains.

 

V. Gasket Adhesion Strength and Promotional Requirements

1. The adhesion strength of the promotional bottle cap gasket is appropriate. It is generally not easy to peel off except when required to be peeled off. The gasket will not fall off naturally after pasteurization;

2. Generally, the adhesion strength of the bottle cap is appropriate. High-quality bottle caps can pass the MTS (Mechanical Materials Testing) test.