A guide to visually spotting green coffee defects

Karmen Yoong
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July 26, 2022
A guide to visually spotting green coffee defects

The quality of coffee in the final cup highly depends on the condition of the green bean. 

If the green coffee is of poor quality to begin with, there is little a roaster can do to provide the best experience for consumers. 

Green coffee defects not only compromise the sensory attributes of coffee, but can cause roasters to lose contracts. This may have a domino effect, leading to financial issues and disruptions within business operations. 

Typically, green coffee goes through a sorting processing at origin, and any defective beans are removed before export. However, some defects cannot be spotted prior to roasting, while others may only develop during transport or storage. 

A physical inspection can help roasters spot green coffee defects and inform them of a coffee’s value and potential. Additionally, it can provide insight into how the beans will behave during and after roasting. 

Find out more about spotting green coffee defects and how they can affect a coffee’s flavour.

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An close up image of a green coffee defect in an article about visually spotting green coffee defects

What are the most common green coffee defects?

Green coffee defects refer to physical flaws and imperfections of coffee beans, which, more often than not, lead to unpleasant flavours. 

It is important to note that defects can occur at any point along the coffee supply chain. 

The Specialty Coffee Association (SCA) has categorised defects into primary and secondary defects. Furthermore, it has outlined a full list of both in the Arabica Green Defect Handbook.

Primary green coffee defects include: full black, full sour, dried cherry, fungus damage, foreign matter, and severe insect damage. 

Secondary defects include: partial black, partial sour, parchment, floater, immature or unripe cherries, withered cherries, broken, chipped, or cut beans, and slight insect damage. 

The SCA evaluates specialty grade coffee using 350g (12.3oz) samples. These must be free from any primary defects and contain no more than five secondary defects. 

Some of the most prevalent green coffee defects are:

Full black and partial black

These coffee beans will appear black, brown, or shrivelled with an enlarged centre cut. This type of defect can occur in the field or during processing. 

Author Jean Nicole Wintgen explains the common causes of this defect in his book, Coffee: Growing, Processing, Sustainable Production. Causes include attacks from pests and diseases, insufficient water during growth, immature beans, over-ripe cherries, and over-fermentation.

Full sour and partial sour

The full sour and partial sour bean defect results from damage during processing or storage. 

Common causes for this green coffee defect include over-fermentation and delays between harvesting and pulping. Additionally, using contaminated fermentation tanks or water, and storing beans while they have too high a moisture content may cause them to go sour.

Generally, the beans are a yellow or light to dark brown colour, with a reddish silverskin. Sour green beans may also smell of vinegar. 

Broken, chipped, or cut beans

These beans are fractured due to mishandling during the depulping, hulling, or milling process. 

Insect damaged beans

Insect damage commonly occurs in the field when the coffee cherries are attacked by coffee berry borers.

Additionally, the defect can occur during storage when coffee bean weevils create holes in the bean’s surface.

Fungus damaged or mouldy beans

Moisture is the chief contributor to the growth of fungus or mould on coffee beans. 

This can occur at any point from harvesting to storage – especially in humid conditions. Spotting this defect is relatively easy, as the beans will have white, yellow, or reddish-brown patches.

An image of three cups of coffee, one black, one strong, one milky, explaining how green coffee defects affect coffee flavour in an article about visually spotting green coffee defects

How can green coffee defects affect flavour?

The flavour and sensory attributes of coffee are directly related to the quality of the green bean. 

“As roasters, our most important limitation is the quality of our ingredient,” says Geoff Watts, co-owner of Intelligentsia Coffee.

He believes producing delicious coffee starts with green beans that are designed to be great. “No amount of roast sorcery can transform a mediocre-quality green lot into a gorgeous cup.”

Notably, green coffee defects can greatly impact a coffee’s flavour. For instance, black beans often produce significantly off-flavours with a loss of aroma, while sour beans often create excessively tart and winey flavours. 

Black and sour beans are also known to roast to a lesser degree compared to other types of beans under the same roasting conditions – producing inferior cup qualities.

Similarly, physically fractured beans tend to roast poorly with uneven heat transfer, which leads to inconsistent flavour development. Broken or chipped beans often taste earthy, dirty, or sour.

Some green coffee defects, such as quakers, are only visible after roasting. Quakers are immature beans that do not contain enough sugars to caramelise during a roast.

These beans remain pale during a roast and tend to produce a dry, papery mouthfeel with an unpleasant bitterness. 

Floater beans refer to those with low density caused by uneven drying or improper storage. However, these are usually spotted and removed at washing stations. 

That said, if found in a roasting batch, floaters may contribute to straw or weed-like qualities, as well as traces of fermented or mouldy flavours.

Mould, microbial, or fungi infections typically introduced during the processing or drying stage may result in stinker beans, which tend to emit an unpleasant odour when crushed or grounded.

An image of coffee beans being sorted in order to visually spotting green coffee defects

How to spot green coffee defects

While green coffees are typically graded and classified before being exported, sorting for defects can be a laborious and difficult process. 

What’s more, as defects can develop at any time, it is unsurprising if roasters find a few hidden in a batch of green coffee.

As such, it is important roasters have the knowledge needed to identify coffee defects. In particular, they should carry out physical inspections of samples before purchase, and inspect it again upon delivery.

Roasters can prepare for an inspection by having equipment on hand. These include a green grading mat, scale, lamp, timer, and a glass of water to check for floaters.

Roasters should scan through a sample size of 350g (12.3oz) for any obvious defects, such as mouldy, broken, or insect damaged beans. 

Other physical attributes such as bean size, volume, density, colour, and water activity are also useful indicators for differentiating between defective and healthy beans.

For instance, in both arabica and robusta coffee, defective beans are often smaller than normal coffee beans. 

Raw coffee beans also tend to come in a wide array of colours, ranging from blue and green to yellow and brown. 

The most desirable colours are blue to grey green, while brownish tones are considered inferior due to its association with ageing, improper drying, and fermentation.

Additionally, roasters must monitor weight loss during roasting. As defective beans are found to roast to a lesser degree, they tend to have lower weight loss value.

Green coffee defects can also be judged by smell and taste, especially for those that only reveal themselves after roasting.

An image of a coffee roaster holding packaged coffee in multilayer kraft paper coffee bags in an article about visually spotting green coffee defects

Once roasters have removed green coffee defects and ensured the highest quality of beans in a roasting batch, preserving coffee freshness is of the utmost importance.

With fully sustainable coffee packaging, specialty roasters can showcase their commitment to the environment as well as preserve a coffee’s freshness. 

At MTPak Coffee, we provide specialty coffee roasters and coffee shops with sustainable high-barrier packaging that will keep your coffee protected from external factors that affect quality. 

Roasters have the option to choose from a range of green materials, including kraft paper, rice paper, low-density polyethylene (LDPE) and polylactic acid (PLA), all of which can be fitted with degassing valves and resealable zippers.

Our team of dedicated designers can also help you to create the perfect design for your packaging, ensuring your coffee stands out from the rest.

For more information on sustainable coffee packaging, contact our team.

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Karmen Yoong
Karmen Yoong

Karmen has been a writer for MTPak Coffee for several years and is very passionate about her craft.

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