Twelve Green Coffee Bean “Defects” That Will Damage Your Roast

Twelve Green Coffee Bean “Defects” That Will Damage Your Roast

Continuing with our Green Bean Series, this month we’re going to take on defects in wet processed Arabica coffee beans; their cause, how to identify them and the effect they have on the roast.

Our “Roasters Tools – Green Bean Series” is a five part evaluation of how the characteristics of green coffee beans affect the outcome of the roast.

Roasters who consistently purchase strictly top grade premium coffees may have only rarely been confronted with defects, while the majority of roasters run across them much too often, even when presented with what is being sold as “Specialty” grade coffees.

The fact is, any one of these dozen defects will negatively affect the quality and alter the taste of the coffee you’re producing. These defects are both identifiable and preventable.

The defects in this article are different than the “formation” defects we talked about in a previous article.

With that in mind, we aim to give you a very straightforward, to the point identification of what these defects look like, their causes, and how they can affect the profile of your roast.

The Twelve Key Defects To Look Out For:

  1. Faded Beans
  2. Amber Beans
  3. Coated Beans
  4. Green Water Damaged
  5. Pulper Damaged
  6. Insect Damaged
  7. Immature Beans
  8. Foxy Beans
  9. Triple Center Cuts
  10. Stinkers
  11. Over-Fermented
  12. Diseased


Faded beans can be a result of either over drying or absorbing excessive moisture, depending on the environment. Either way, faded beans have a low resistance to environmental factors.

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

Normally, they result from beans that have a high moisture content (11% – 13%) and when stored in a warehouse, they’ll tend to dry out. In the process of drying out, and because they are not in contact with direct sunshine, these beans tend to fade.

Instead of drying, these beans are actually rotting and developing molds inside. It’s these molds that cause the beans to dry excessively, producing their pale to whitish brown color.

In addition, during the drying of wet or dry processed beans, the coffee can be negatively affected if not properly exposed to sunshine at the appropriate stage in the drying process.

Another cause is when coffee has been over-hulled using a hammer mill. In this case, the beans will come out with a dull color as a result of the outer cells being bruised and microscopic dust permeating the outer layer of the beans.

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


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

When you roast these beans, the cup will be lacking in acidity, with a flat harsh body and a bitter flavor. Also, the roast produced by these beans will be very dull in color.


These beans have a sticky silver skin caused by either overbearing or from being drought affected. The characteristics of these beans look whitish, rough and display microscopic lines from the silver skin.

In the process of roasting, you’ll experience soft beans with excessive chaff. The roast can result in negative effects in the cup, including excessively high grassy, hay, earthy, woody, greenish and potato flavors.


These are fully processed beans that, when hulled, get in contact with water where a chemical reaction takes place, turning the beans a greenish color. This situation results in the beans becoming moldy and toxic.


In the process of going through the pulping machine, coffee beans can get stuck, creating excessive pressure which causes the beans to become wounded.

These wounded beans will burst and then begin to slightly oxidize, become contaminated with water and over ferment, causing molds which result in earthy, leather and musty flavors.

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


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

Antestia bugs damage beans causing them to bruise, which produces rough black to yellow-like colored spots.

Beans with these types of insect damage will give a soft roast and the beans will tend to shrink, creating dominant musty, alkaline and salty flavors.


Picked under-ripe, often as a result of overbearing and drought affected conditions, the characteristics of immature beans include a rough surface and greenish color with a sticky silver skin and will usually have thin edges.

The roast will be very dull, with open center-cuts, soft beans and subsequently produce no acidity, heavy body, with greenish and grassy flavors.

These beans can also lead to Quakers in the roast; visible only after roasting by their pale appearance and flat peanut butter taste. Avoiding the purchase of immature beans is the best way to avoid contamination by these defective beans.


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

This rusty-red color is generally brought about by the beans being over-ripe. These beans tend to have a dead embryo and will give you fruity fermented and nutty flavors.


These are deformed beans caused by malnourishment due to either drought affected conditions or lack of minerals, creating ragged beans with multiple center cuts.

During the roast, these beans can 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 taste.


Stinker beans can have a normal formation, but have a dead embryo and are yellow in color caused by over-fermentation and/or over-ripe. If crushed, broken or cut open when raw, they put off an order that’s very unpleasant.

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


These beans look soiled and have a tobacco color.

When roasted you’ll get a pulpy, sour flavor and unclean, dirty cup; with a smell of rotting flesh or a cow shed aroma. If only slightly over-fermented, your roast may give sour and onion flavors.


These defects are brought about by the coffee being affected by various diseases like CBD (Coffee Berry Disease) and Leaf Rust.

When disease strikes a coffee farm, the mother plant will produce beans that are premature. This will affect the berry before it ripens, usually at the milk stage, and the beans will either not develop at all or only partially develop, with a very small berry or nonexistent berry inside the parchment within the cherry.

The deformed part of these beans looks somewhat brownish to very dark brown in color, often with deformities that resemble a chipped off piece where the bean is left with dark brown marks which go deep into the bean. The deformed part of these beans is generally flaky and ragged in formation.

These small diseased beans will be only partially developed, but can still be harvested and end up mixed with other beans of normal quality, then sold in the marketplace.


  • First, avoid these nasty defects when you’re purchasing green coffee whenever possible.
  • Second, educate your customers about the tastes inherent in a quality cup. An uneducated palette can even get accustomed to over-fermented, moldy, musty, peanut-buttery and other flavor defects that are actually toxic when ingested into the human body!
  • AND, continue your quest to create the perfect roast!

Leave a Reply