How does light affect roasted coffee?

Karmen Yoong
May 11, 2022
How does light affect roasted coffee?

Coffee is an agricultural product, and like any organic produce, it is susceptible to degradation of quality over time.

Exposure to external factors such as oxygen, heat, moisture, and light will significantly reduce the shelf life of roasted coffee. Notably, the most detrimental of these is light.

When roasted coffee is exposed to light for long periods of time, it causes the chemical compounds in the beans to break down. Known as “photodegradation” it can lead to a loss of aroma and flavour, resulting in a stale and bland cup of coffee.

This will not only drive customers away, but waste the efforts of everyone involved along the supply chain. Therefore, it is essential roasted coffee is stored effectively to preserve its freshness.

To understand more about how light affects roasted coffee, I spoke with WBC-certified judge and WCE representative, Danilo Lodi.

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Five lit carbon filament pear shaped light bulbs hanging in a line.

What do we mean by “light”?

Light is a form of energy that travels in electromagnetic waves.

Different kinds of light can be found on the electromagnetic spectrum, depending on the wavelength and frequency.

The electromagnetic spectrum is broad. It ranges from low frequency radio waves with wavelengths measured in metres to high energy gamma-rays with wavelengths shorter than 1 x 10-10  metres.

The human eye can only detect wavelengths from 380 to 700 nanometres. This is referred to as the visible light spectrum, and the wavelengths are perceived as colours of the rainbow.

Electromagnetic waves that fall outside of the visible light range are undetectable, for instance, ultraviolet (UV) and infrared (IR) radiation.

As light comprises photons which carry energy, it causes a phenomenon known as “photodegradation”. This refers to the erosion of material caused by the exposure to photons or light, and can affect everything from organic produce, paintings, to artefacts.

In the presence of oxygen, photodegradation occurs through photooxidation: the degradation of a surface due to the combined action of light and oxygen.

Moreover, photodegradation includes photodissociation, whereby the chemical compounds in substances are broken down into smaller pieces. At the same time, it permanently alters the molecular shape of the chemical compounds.

While photodegradation occurs more severely with UV radiation from the sun, other sources of light can also negatively affect the quality of materials.

Roasted coffee grounds sitting in sunbeam, placed in a white wax paper bag.

How does light affect roasted coffee?

Coupled with oxygen, heat, and moisture, light is an external stimulus that significantly contributes to the deterioration of coffee freshness.

“People often only think about oxygen when we talk about the oxidation of coffee,” says Danilo, who is also a green coffee buyer and farm consultant. “But light actually has an effect as well, as it can speed up the oxidation process.”

Danilo explains there have been many studies on oxidation of cheese and wine due to light exposure.

“One thing these studies have in common is that light speeds up the oxidation of lipids,” Danilo says. “Applying the same to coffee, this will accelerate the loss of flavour and aroma in coffee.”

This is because lipids retain aroma in coffee. A study done on Central American coffee found a direct correlation between fat content and beverage quality. Coffees that are exposed to light tend to have stale flavours and aroma, with metallic, bitter, or rancid notes.

Furthermore, the rate of photodegradation is influenced by wavelength of light. For example, ultraviolet A (UVA) light has a longer wavelength and is often associated with skin ageing. Ultraviolet B (UVB) light has a shorter wavelength and can cause the skin to burn.

“UVA and UVB will significantly decrease the quality of coffee,” Danilo says. “However, LED and artificial light are also known to damage coffee.”

Other than the properties of light, photodegradation depends on the condition of the coffee. Danilo explains ground coffee degrades faster than whole beans as there is a larger surface area for light to act on.

Additionally, dark roasted coffee with a more porous cellulose structure tends to go stale quickly, as it loses oil faster than light and medium roasts.

White kraft paper multilayer coffee bags filled with roasted coffee beans sitting on wooden shelf.

How can roasters reduce light exposure?

As soon as a roast is complete, the coffee’s flavours and aromas must be locked in immediately, and the beans protected against damaging external elements.

Typically, roasted beans are left to rest, allowing them to degas sufficiently before being packaged. Degassing allows the beans to release built-up carbon dioxide (CO2) and helps prevent the packaged bags from looking bloated on the shelf.

During the degassing period, Danilo says using opaque storage containers can help prevent light exposure. Once roasted coffee has degassed sufficiently, roasters can use light-resistant packaging to preserve its freshness.

For instance, multilayer coffee bags have several layers that act as a strong barrier against light, moisture, heat, and oxygen.

This packaging often uses sustainable materials such as polyethylene (PE) and low-density polyethylene (LDPE) for the inner lining, and kraft paper or rice paper for the outer layers.

Another way roasters can protect their coffee is to store it in shaded areas where there is no direct exposure to heat or sunlight.

Furthermore, Danilo reminds roasters to be mindful of the time between resting and packaging.

“Typically, the time frame is between 24 and 72 hours,” Danilo says, “But it depends on where you are located.

“If your roastery is at a higher altitude, you will have less oxygen and can work more during the day. However, if you are close to sea level, you should consider a maximum of 24 hours for the resting period.”

Similarly, weather may affect the rate of photodegradation, as heat speeds up the oxidation process. Therefore, it is crucial roasters work in a controlled environment where temperatures do not exceed 25°C (77°F).

By controlling these factors, Danilo says roasters will have more control over the freshness of their end product. More so, by investing in sustainable, multilayer packaging, roasters can ensure consumers enjoy quality coffee in every cup.

White kraft paper multilayer coffee bag being held up to lit eddison light bulb by female Caucasian hand.

At MTPak Coffee, we offer a range of environmentally friendly packaging that will both protect your coffee from light exposure and showcase your commitment to sustainability.

Our multilayer pouches use PLA laminates to maintain the recyclable and compostable properties of the packaging, while providing additional barriers to oxygen, light, heat, and moisture.

Meanwhile, our customised design and labelling provides an added avenue for roasters to guide consumers on the right way to store coffee.

For more information on multilayer coffee bags, contact our team

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