Coffee’s flaws: the aroma we don’t like

Hey, do you think every donut has a hole? Well, not every coffee has that amazing smell we all love either. So, let's learn about the flaws in coffee and how to spot them when we're drinking it.

Barbara Fassio
Barbara Fassio
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Coffee is a beverage loved by many because of its ability to awaken the senses and offer a wide range of flavours and aromas. However, not all cups of coffee are the same: some may contain defects that negatively affect the taste and aroma. These defects may be present at the origin, in the beans, or result from mistakes in processing or extraction. In this article, we will explore the most common coffee defects and their effects on the taste and aroma of the beverage. If you love coffee, you will discover how to recognise these defects and how to avoid spoiling a good cup of coffee.

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The natural defect

“Nature provides an abundance of marvelous fruits, species, and varieties which, when mixed with the diversity of possible terroirs, allow us to obtain coffees with an array of unique aromas and scents. The wonderful notes that ripe and well-groomed beans can offer are then further enhanced by our work as roasters. However, nature is also subject to incredible variability in terms of unforeseen events that can damage its products, including cherries and coffee beans. As a result, the quality of the coffee can suffer, and it may become undrinkable.”


The mould that causes this defect is clearly visible on the green bean, which can be affected during drying or storage if the beans are not treated properly. The resulting coffee does not lose its mouldy or damp earthy smell, it can be rather sour and bitter, with a decidedly unpleasant aftertaste.

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Have you heard of ‘floaters’ before? They’re basically coffee beans that have gone bad because of bacteria or bad processing, and you can spot them by their light color and different density when you put them in water. If you’re tasting coffee and you come across a floater, it’s not going to be a pleasant experience. It’ll taste bitter and woody with a strong hint of roasted peanut. So make sure to keep an eye out for those pesky floaters!”


Did you know that there’s a coffee bean that’s totally black and the exact opposite of a floater? Unfortunately, this is a serious defect that coffee professionals categorize as a primary one. When this type of bean is brewed, it can cause bitterness, sourness, and even taste like ashes. These black beans are black because they’re rotten, which can happen for a few reasons, like if they were picked too late, didn’t get enough water while they were growing, or went through an extended fermentation period.”


Do the beans arrive at the roastery perforated? Are there little ‘tunnels’ running through them? These are caused by coffee parasites, which infest the coffee plant and gnaw the beans: when roasted and ground, they unfortunately leave a tarry note and a very bitter aftertaste.

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Coffee is said to be dirty when foreign bodies are present in the beans, such as twigs, leaves and stones. These may mistakenly be attached to the beans during harvesting and, if not perfectly sorted afterwards, be roasted together. The resulting cup will have an earthy aroma, with notes of undergrowth and vegetation as well as a sandy, dirty feel.

It is part of the history of a product to have some flaws, the variety and beauty of nature is made of imperfection: this is where the work of passionate producers and roasters like us comes in. The selection of only healthy beans is essential in order to be able to produce a beverage with a wide variety of scents and aromas, but always very pleasant.

Damage from processing

As we know, coffee undergoes a lot of processing before it can be tasted and sometimes… something goes wrong!


A coffee with a chemical and sour smell, similar to that of paint thinner or a cleaning product comes from beans that have been in contact with chemicals during processing (pesticides, herbicides or other substances used to treat the beans). The taste is decidedly bitter and unpleasant, with a lingering aftertaste.


Acidity in coffee, if fine, is often a very positive characteristic. Unfortunately, however, the fermentation process can get out of hand and, if the beans are not washed or dried properly, the end product will be sour. Sour coffee has a pungent, acetic aroma.


The third defect is ‘over-roasting’. This defect occurs when coffee beans are subjected to too high a temperature or for too long during the roasting process. Burnt coffee tastes flat and lacks the complexity that properly roasted coffee has. If it goes well, it can be recognised by the lack of aroma and taste; if it goes particularly badly, it can be recognised by the ash taste and burnt hints.

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Woody coffee is caused by poor storage conditions. Coffee stored in humid conditions can develop a woody taste. Are you drinking a cup that tastes like cardboard, leaving you with the sensation of a dry, watery product? Forget it, it is woody.

If you’re roasting coffee, it’s essential to find the perfect roasting curve every time. And if you’re brewing it, you need to take extreme care of your equipment – a dirty grinder or a cup that smells like dish soap isn’t exactly what we have in mind when we talk about good gear, right? Only by paying attention to these details can you experience the wonderful bouquet of aromas that coffee has to offer. But be careful, once you get hooked on the taste, you won’t be able to resist it!