Twelve green coffee beans "Defects" That will damage your roast

Continuing our Green Beans Series, this month we’ll be looking at defects in wet-processed Arabica coffee beans; their cause, how to identify them and the effect they have on the roast.

Our “Tools for Roasters – Green Beans Series” is a five-part evaluation of how the characteristics of green coffee beans affect the roast result.

Roasters who consistently purchase strictly premium premium coffees of the best quality may have rarely encountered defects, whereas most roasters encounter them far too often, even when presented with what is sold as “specialty” coffees. “.

The fact is that any one of these dozens of defects will negatively affect the quality and alter the flavor of the coffee you are producing. These defects are both identifiable and preventable.

The flaws in this article are different from the “training” flaws we talked about in a previous article.

With that in mind, our goal is to give you a very direct and accurate identification of what these defects look like, their causes, and how they can affect the profile of your roast.

The twelve key flaws to watch out for:

  1. Faded Beans
  2. amber beans
  3. Battered Beans
  4. damaged green water
  5. damaged pulper
  6. damaged insect
  7. immature beans
  8. sneaky beans
  9. triple center cuts
  10. stinky
  11. over-fermented
  12. sick


Wilted beans can be the result of overdrying or excessive moisture absorption, depending on the environment. Either way, wilted beans have little resistance to environmental factors.

The effect on the roast is that they give a dull roast regardless of the roast profile. The result is a smooth bean with flavors of moisture and wood in the cup. And, the percentage of moisture loss will be very high. The color of these beans is pale brown, whitish.

They are normally the result of beans that have a high moisture content (11% – 13%) and when stored in a warehouse they will tend to dry out. In the drying process, and because they are not in direct sunlight, these beans tend to wilt.

Instead of drying out, these beans are actually rotting and molding inside them. It is these molds that cause the beans to overdry, producing their pale brown to off-white color.

Additionally, during the drying of wet or dry processed beans, the coffee can be adversely affected if it is not adequately exposed to sunlight at the proper stage of the drying process.

Another cause is when the coffee has been hulled with a hammer mill. In this case, the pimples will come out dull in color as a result of the outer cells being bruised and microscopic dust getting into the outer layer of the pimples.

A final factor that can contribute to coffee discoloration is older coffee that has been kept in a warehouse for two to three years or more, causing the beans to dry out, develop mold, and other negative consequences.


These beans have a bright shiny golden color. The cause is due to mineral deficiencies in the soil (including iron).

When you roast these beans, the cup will lack acidity, with a rough, flat body and a bitter taste. Also, the roast produced by these beans will have a very dull color.


These beans have a sticky, silvery skin caused by dominance or being affected by drought. The characteristics of these beans look whitish, rough and show microscopic lines of silvery skin.

In the roasting process, you will experience soft beans with excess chaff. Roasting can result in negative effects in the cup, including excessively high flavors of grass, hay, earth, wood, greenish, and potato.


These are fully processed beans that, when shelled, come into contact with water where a chemical reaction occurs that turns them a greenish color. This situation causes the grains to become moldy and toxic.


In the process of going through the pulping machine, the coffee beans can get stuck, creating excessive pressure that causes the beans to be damaged.

These wounded beans will pop and then begin to oxidize slightly, become contaminated with water, and over-ferment, causing mold that will result in musty, leathery, earthy flavors.

Also, roasted beans will be uneven; some will split while others will appear round and mixed with the solid beans.


Berry moths inject the coffee cherry in the process of laying eggs, creating a needle-like black hole.

Anthestia insects damage beans and bruise them, producing rough black to yellow spots.

Beans with this type of insect damage will give a light roast and will tend to shrink, creating dominant musty, alkaline, and salty flavors.


Harvested immature, often as a result of drought-affected and prevailing conditions, characteristics of immature beans include a rough surface and a greenish color with a sticky silvery skin and will typically have thin edges.

The roast will be very dull, with open center cuts, soft beans, and later will not produce acidity, heavy body, with greenish and herbaceous flavours.

These beans can also give rise to quakers in roasting; visible only after grilling because of their pale appearance and peanut butter flavor. Avoiding the purchase of unripe beans is the best way to avoid contamination from these defective beans.


As you can imagine, the name comes from the color of a red fox.

This rusty red color is usually due to the beans being overripe. These beans tend to be embryo-dead and will give you fruity, fermented, and nutty flavors.


These are misshapen beans caused by malnutrition due to drought-affected conditions or lack of minerals, creating jagged beans with multiple cuts down the center.

During roasting, these beans may split open at their double or triple center cuts. They are fragile, soft and very permeable; which will over-roast, creating a heavy body, a flat cup, and a smoky, burnt flavor.


Stinker beans may have a normal formation, but have a dead embryo and are yellow in color due to over-fermentation and/or over-ripening. If they are crushed, broken or cut when raw, they postpone an order which is very unpleasant.

Even one or two stinkers in your roast can ruin the whole batch and give you a disgusting cuppa.


These beans look dirty and have a tobacco color.

When roasted you will get a sour, pulpy taste and a dirty, filthy cup; smelling of rotten meat or barn. If only slightly over-fermented, your roast can give off tart and onion flavors.


These defects are due to the fact that coffee is affected by various diseases such as CBD (coffee berry disease) and leaf rust.

When the disease attacks a coffee farm, the mother plant will produce premature beans. This will affect the berry before it ripens, usually at the milk stage, and the kernels will either not develop at all or only partially develop, with either a very small berry or no berry within the parchment within the cherry.

The deformed part of these beans looks brown to very dark brown, often with deformities that resemble a chipped piece where the bean is left with dark brown markings that go deep into the bean. The deformed part of these beans is usually scaly and irregular in shape.

These little diseased beans will only partially develop, but can still be harvested and finished mixed with other normal quality beans and then sold in the market.


  • First, avoid these nasty blemishes when buying green coffee whenever possible.
  • Second, educate your customers about the tastes that go into a quality cup. An uneducated popsicle can even get used to overly fermented, moldy, rancid, peanut butter and other flavor defects that are actually toxic when ingested into the human body!
  • And continue your quest to create the perfect roast!

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