Aluminium vs. PLA: Which is better for coffee bag interiors?

Jane Merchant
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September 13, 2021
aluminium lined coffee bag

The benefits of sustainable packaging materials are obvious: they reduce carbon emissions, improve customer satisfaction, and contribute to a circular economy.

However, one of the concerns around compostable, recyclable, and biodegradable coffee bags is freshness.

Many wonder, for example, how a rice paper pouch, which can decompose in as little as 90 days, will adequately prevent exposure to moisture, oxygen, and light.

In most cases, the solution is an interior lining. Interior linings help reinforce sustainable materials, creating an additional barrier against external factors that can affect the quality of the coffee inside.

When it comes to interior linings, the most popular choices are aluminium foil and polylactic acid (PLA). Aluminium foil is one of the most abundant raw materials on earth, while PLA is a bioplastic made from renewable resources.

Although both are highly effective as additional barriers for sustainable packaging materials, each one comes with its own set of pros and cons.

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aluminium lined coffee bag
Multilayer packaging helps preserve the freshness of roasted coffee

Why do coffee bags need an interior lining?

Since the 1960s, freshness has been a key factor in high-quality coffee.

Broadly defined as the original, unimpaired qualities of coffee, its preservation is deemed essential if customers are to enjoy all the nuances of flavour and aroma.

While the time between roasting and consuming plays a key role in the freshness of coffee, it is largely determined by the level of exposure to four external factors: oxygen, light, moisture, and heat.

If the coffee comes into contact with any of these “enemies” over a long period of time, it will lead to the degradation of aroma and the development of rancid flavours, along with the overall staling of the coffee.

As a result, most roasters opt for flexible multilayer packaging to preserve freshness and prolong the shelf life of their coffee. Multilayer packaging protects the coffee by creating an effective barrier against external factors. 

They can be added to a whole host of other materials that offer limited protection by themselves, including kraft paper and rice paper.

Multiple layers are formed by coextrusion, lamination, or various coating technologies using lightweight materials that range from plastics to metals. However, the two most commonly used in coffee packaging are aluminium foil and polylactic acid (PLA).

aluminium lined coffee bag
For decades, aluminium foil lining was the go-to choice for roasters

Aluminium lining

Benefits

Aluminium is third only to oxygen and silicon as the most abundant element in the earth’s crust. It is infinitely recyclable and relatively low-cost, making it a popular material for lining coffee bags.

Aluminium foil’s barrier properties are among the best available.Not only is it physiologically harmless to food, it is resistant to water, water vapour, grease, gas and fire, it reflects light, heat, and UV rays, and it does not charge electronically. It can also be painted and printed to meet the requirements of modern packaging.

A Spanish study evaluating different types of containers for the storage of mandarin juice found that aluminium foil far exceeded the other materials in preserving the quality of the drink.

Compared to PET, and cardboard with polyethylene, the container with an aluminium foil interior performed better at keeping out oxygen, and preserving the colour, flavour, and aroma of the mandarin juice.

Of all aluminium ever produced, 75% is still in use today. This saves a significant amount of energy, as recycling aluminium requires around 90% of the energy used to extract aluminium from its ore – a complex and costly process.

Drawbacks

For decades, aluminium foil has been the go-to for coffee bag interiors, with around seven billion aluminum foil containers still produced annually – but they’re not without their downsides.

One of the issues concerns recyclability: although aluminium is infinitely recyclable, it must be separated from the other layers before it can be melted down and reused.

In order to do this, the used coffee bag must be taken to a specialised recycling facility with the equipment to separate the materials.

However, customers are not always aware of these special requirements, which results in the aluminium foil lined coffee bags being disposed of incorrectly.

Instead of going to a recycling facility, they end up going to landfill where they break down and emit methane, a potent greenhouse gas.

Problems with aluminium foil lined coffee bags also stem from the thickness of the foil. 

Generally, the thinner and more flexible the foil, the more likely it is to develop microscopic tears and pinholes. If this happens and oxygen, light, moisture, or heat enters, it will quickly compromise the coffee’s quality and staleness.

pla lined coffee bag
In a commercial composting facility, PLA can break down in as little as 90 days

PLA lining

Benefits

PLA is a toxin-free bioplastic made from the fermentation of carbohydrates from renewable resources such as maize, cornstarch, and sugarcane.

While the fermentation produces resin filaments that have similar characteristics to petroleum-based plastic, PLA can break down in as little as 90 days when placed in a commercial composting environment. This is compared to the 500 years typical of traditional plastics.

PLA is widely used as a laminate for coffee packaging materials such as kraft paper and rice paper. It has a high tensile strength (7,000 psi), can withstand temperatures of up to 420°F, and has good water vapour and humidity barrier properties.

According to research, PLA lined bags can protect the contents from moisture and oxygen for up to 12 months, making it a good choice for coffee that will spend long periods of time in transit or in storage.

Drawbacks

Like aluminium foil, the downsides to using PLA derive from confusion over its recycling.

While it’s compostable, it must degrade in a controlled environment at a specific temperature and with certain microbes present. If this doesn’t happen, it won’t fully degrade and will make the soil it ends up in highly acidic.

Recyclers are wary of PLA, as too frequently it’s disposed of with conventional plastics. The process to separate the two is painstaking and expensive.

It means that if you use it as a bag interior material, you must ensure that facilities exist to process it and that customers can recycle it quickly and conveniently.

pla coffee bags
PLA lining can be used across a range of packaging materials, including kraft paper and rice paper

As the world moves away from packaging materials that have a negative impact on the environment, PLA is steadily replacing aluminium foil the go-to choice for coffee bag interiors. Not only is it compostable, lightweight, and widely available, it also offers similar barrier properties to aluminium, helping to effectively preserve the freshness of coffee.

MTPak Coffee offers a range of coffee bags that can be fitted with a PLA interior. When added to kraft paper, it produces a fully compostable option for customers.

For information about our PLA lined coffee bags, contact our team.

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Aluminium vs. PLA: Which is better for coffee bag interiors?

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