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Coffee defects

Now, why might it be that a cup of coffee tastes off? Besides a bad roast or old stale coffee we must keep in mind that coffee beans are natural products and might be affected by a whole range of things that we refer to as coffee defects. In this article we will look at a range of reasons why coffee beans might taste off.


What are the different defects?

Below we will look into most common defects and how and why they might affect the taste of your coffee.

Fully black or partially black beans

The coffee beans will look black/brown and shrivelled, and the crack in the middle of the bean will be much wider than compared to a “healthy” bean. There are a few different reasons why this might happen. Fungal diseases and nutritional deficiencies, lack of water during the growing period and possibly over-fermentation or over-ripe cherries picked from the ground (and not the tree), all of these things can lead to full or partial black bean.

 If a black bean ends up in the roast it will end up giving the coffee an unpleasant aroma and is often said to taste medicinal or smoky, some even say it gives the coffee fishy notes.

Full Sour & Partial Sour Beans

These beans will light brown, red or yellow looking. When you scratch the bean, you might get a vinegary smell. The common cause for sour beans is delays between picking and depulping the cherries, over-fermentation, storing the beans with too high moisture content and using dirty water during processing.

The effect is an underdeveloped flavour, with grassy and sour notes.

Broken or Crushed Beans

Broken beans can be caused by machinery during depulping, drying or milling the coffee. It can also be caused by the moisture content of the coffee being low and finally if the coffee cherries are unripe and green when picked.

Broken and crushed beans will lead to the coffee being roasted poorly and the heat spreading unevenly between the beans. The flavour will be inconsistent and unbalanced.


Quakers are unripe beans who have an ashy and dry taste to them. You’ll spot them after roasting the coffee as they will be lighter coloured as they won’t roast properly due to lacking the sugar required to get caramelised.

Insect damage

This can either be spotted on the cherries when picking and you should be able to see tiny holes in the beans. Different insects can have different effects on the coffee, they can leave a sour note or worse they can lead to mould in the beans. A common enemy of coffee productions is the berry borer. The berry borer is one of the biggest problems in coffee production. If berry borer establishes itself at a coffee plantation it will spread fast and if the farmer is unlucky, it can ruin a whole crop. It’s a reason why many farmers are against growing organic coffee as they are afraid that if they don’t spread pesticides, they might lose the whole crop. 

Damage from fungus

Often caused by insect holes allowing moisture into the bean which then allows mould and fungus to build up. You can detect the fungus when spotting grey, reddish or white spores on the beans. The impact on the coffee is earthy and over-fermented flavours.


It must be said that most of time these defects are caught well before the coffee reaches the end consumer. Either by the machinery used along the way to process the coffee, or by the keen eyes of the people work at the coffee plantations or by the roastery so chances are that you never have to experience the effect of coffee beans with defects.

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