January 25, 2018

Coffee Defects & How to Avoid Them: A Producer’s Guide

Producers, you need to be aware of coffee defects. They can affect the way your beans roast and taste, and as of such, their value. They may even cause you to lose contracts. Some defects are more dangerous than others; some are more widespread than others. But it’s important that you can recognize the most common ones, the impact they’ll have on your harvest, and how to prevent them. So, let’s take a look.

Lee este artículo en español Guía del Productor: Defectos del Café & Cómo Evitarlos

Coffee cherries

Freshly harvested coffee cherries in Tanzania. Credit: Megillionvoices via Wikimedia Commons, CC BY-SA 4.0

What Is a Coffee Defect?

A defect is any characteristic that doesn’t meet quality control standards, and can be the result of farm conditions, processing, or even roasting. Fortunately, producers can remove defective beans through sorting. But if a defect goes unnoticed, it will become apparent during roasting and coffee consumption.

There are different kinds of defects: primary ones (the worst ones) and secondary ones (which are still bad, but not as bad). For specialty coffee, a 300-gram sample should have zero primary defects and five or less secondary ones. You would expect commodity-grade coffee to have more defects per sample – “exchange-grade” coffee, for example, can have as many as 23.

And sometimes, you need up to five of the defects in question for it to be registered as a defect.

So, what are the different defects? This table from the FAO explains it all:

Table of defects
information Table

Green coffee bean defects. Credit: FAO

What Do Defects Mean for Producers?

Anne Lunell is the Co-Owner of Koppi Roasters in Sweden. She tells me, “Defects can have an impact on a producer’s future. If it is bad defects, the risk is that the coffee gets rejected and that the producers lose parts of their income.”

As a roaster, she avoids working with producers if there are too many defects in their lots. “We always hand sort our coffee after each roast,” she explains, “and of course the amount of defects affects the amount of time we have to spend doing this. If there are too many defects, we would likely not buy the coffee again. We have worked with the same producers for many years and them always delivering consistently high quality is an obvious reason. To know that the coffee is easy to work with (very few defects, well processed, keeps well over a long period of time etc ) is utterly important.”

You might also like: 4 Ways Coffee Producers Can Increase Their Profits

For producers, following rigorous quality control to remove defects can be expensive; however, this is also one of the reasons why specialty coffee pays more than commodity-grade beans. The price premiums should in theory compensate the extra labor and equipment – assuming producers have the right know-how.

Washed beans

Coffee cherries and washed coffee beans dry on raised beds in Tarrazú, Costa Rica. Credit: Tarrazu via Wikimedia Commons, Public Domain

Common Green Bean Defects

There are many, many coffee defects that may affect a producer’s crop. Some of the most common defects that you need to be aware of, due to their impact on production and profitability, are:

1. Full Black & Partial Black Beans

How can you recognize them?  

The coffee beans will look black or brown and shrivelled, while the crack down the middle will be too wide.

Why does it happen?

This is sometimes the result of a lack of development; Anacafé explains that fungal diseases and nutritional deficiencies can cause this. A lack of water during the growing period can be another cause. Alternatively, as Café de Colombia states, over-fermentation or over-ripe cherries picked from the ground, rather than the tree, can lead to full or partial black beans.

What effect does it have?

If one of these gets into a coffee lot, it will produce an “off flavor” and an unpleasant aroma. It has been described as creating a phenolic or fishy note; at other times, the beans can taste fermented.

What can you do?

Ensure proper plant nutrition and watering, pay attention to the development of fungal diseases, and be careful with fermentation.

green coffee

A green coffee bean sample ready for inspection. Credit: Ana Valencia

2. Full Sour & Partial Sour Beans

How can you recognize them?

The coffee beans will be a light brown, red, or yellow. The silverskin can be a reddish-brown. When scratched, they may have a vinegary smell.

Why does it happen?

Common causes include delays between picking and depulping, over-fermentation (either during processing or on the branch), storing the beans with too high a moisture content, and dirty water.

What effect does it have?

These beans can create an underdeveloped, sour, or grassy flavor.

What can you do?

Make sure to quickly de-pulp the cherries (unless you’re processing naturally), be careful with fermentation and drying, and always use clean water.

You may also like: How to Improve Quality When Drying Washed Coffees

Coffee defects

Samples of various coffee defects. Credit: Anna Oleksak

3. Broken or Crushed Beans

How can you recognize them?

One of the easiest defects to spot, the beans will either be broken or have fractures.

Why does it happen?

It can be caused by machinery during the depulping, drying, and milling processes. Poor moisture content can be a contributing factor, as can picking under-ripe, green cherries.

What effect does it have?

The coffee will roast poorly, with the heat transferring unevenly through the beans. The result? An unbalanced, inconsistent flavor. Moreover, because the beans are cut open, they might develop other defects such as mold.

What can you do?

Look after your machinery and pay attention to moisture content and ripeness.

Coffee beans

Coffee beans dry on a patio. 

4. Quakers

How can you recognize them?

These are unripened, smaller beans with a low density. They’re hard to spot after depulping but are more noticeable once roasted, when they have a lighter color.

Why does it happen?

Quakers are generally caused by poor nutrition, poor picking practices, and drought or coffee leaf rust.

Learn more! Read A Producer’s Guide to Soil Management & Farm Conditions

What effect does it have?

You can expect a dry, papery taste in the cup.

What can you do?

Be careful to only pick ripe coffee.


A bowl full of quakers that have been removed from a roast. Credit: Miguel Binetti

5. Insect Damage

How can you recognize it?

The green beans will typically have small holes; you can also see these on the cherry during picking.

Why does it happen?

A range of insects feeds on the coffee while it’s on the tree or during storage, the most widespread of which is the coffee berry borer. What’s more, because of the holes, mold may start to develop.

What effect does it have?

The impact will depend on the pest itself, but it can range from a muted flavor to sour notes.  

What can you do?

Regularly inspect your crops for infestations, consider pesticides if you’re not an organic farmer, and use insect traps.

coffee cherries

Coffee cherries ripen on the branch.

6. Fungus or Mold

How can you recognize it?

You can see white, yellow, grey, or red spores on the beans.

Why does it happen?

As you might expect, it all comes down to moisture: overly long fermentation periods, interruptions during drying, storing beans with a high moisture content… For this reason, producers in humid environments should be very cautious about using natural or honey processing methods. What’s more, damaged beans – broken ones or ones with insect holes – are more susceptible.

Mold will usually infect an entire batch of coffee, as the spores spread from one bean to another.

What effect does it have?

You can expect moldy, earthy, and over-fermented flavors in the cup.

What can you do?

Pay attention to humidity, only process naturals and honeys if you live in a suitable climate or have appropriate technology, take care if there is unexpected rain, remove insect/machine-damaged beans as early as possible, and sort quickly if you see any moldy beans.

Coffee with defects

A bowl full of defects. Credit: R. Miguel Meza

7. Potato Defect

How can you recognize it?

It’s unfortunately very hard to notice the potato defect in green beans; producers should, instead, watch out for potential bug infestations – yes, this is actually another form of insect damage! However, it’s a particularly unusual one and requires different treatment

Why does it happen?

This is caused by the Antestia bug, which can be found in East Africa. Rwanda and Burundi are the most affected.

What effect does it have?

The roasted coffee tastes and smells of raw potato.

What can you do?

Regularly inspect your crops for infestations, consider pesticides if you’re not an organic farmer, and use insect traps.

Coffee laboratoty

Learning about coffee defects before cupping them. Credit: William Sue

General Tips for Avoiding Defects

We’ve already looked at specific techniques for each coffee defect. However, there are also some general tips that producers can follow to avoid these – and other! – defects from occurring. For a start:

Of course, no two farms are the same. It’s also worth speaking to a local agronomist who can advise on your specific climate, terroir, and context.

Latte art

A specialty cappuccino requires quality at every stage.

Avoiding defects and sorting coffee demands hard work, time, and labor – but if we want to access the specialty market, it’s imperative. As Anne says, “If you want to get paid more and target the speciality coffee roasters, quality is key.”

You might also like: 4 Ways Coffee Producers Can Increase Their Profits

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