Roast Flaws and How to Spot Them

The roasting process has undergone numerous transformations. For example, the coffee beans underwent a significant transformation from the traditional dark roasting procedure to the most recent era of light roast.

In this article, we’ll discuss roast defects and how to spot them in a cup. The roasting procedure is a complex process requiring extensive knowledge of green beans and chemistry.

A brief overview of the roasting process

Some things change inside the green bean during the roasting process. These are the primary factors that can spoil a batch of coffee.

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Structure, density, brittleness CO2, and other factors exert pressure inside the green bean, dramatically affecting its internal structure. As a result, it changes from hard and rough to brittle, less dense, and more porous.

Humidity and weight are important considerations. The weight of the green beans drops by around 15-20 percent when the moisture and organic compounds evaporate from the beans.

Along with this, the bean loses its silvery skin nearly completely, with only faint indications remaining in the center crack (lighter color).

Color. The color changes from green to the typical “brownish” of the perfect roast as the sugars caramelize and the cellulose carbonizes.

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Volume. The pressure exerted by the gases inside the beans increases their volume by 40 to 60 percent. This causes the beans to grow slightly larger as well.

Organic compound depletion. Sugar and water content can both significantly decrease. The caffeine content remains nearly unchanged.

Aromas and essential oils Simultaneously, roasting causes the pyrolysis of hundreds of volatile odorous compounds.

The more time the roasting process takes, the more oil droplets appear on the bean’s surface.

As previously stated, this is a brief overview of what occurs during the roasting process. In some cases, the bean undergoes all of these changes, ranging from 25° C/77 F to nearly 240° C/464 F.

We provide an overview of these facts because it’s easier to understand roast defects when you understand what’s happening inside the bean. Each of them can have an impact on the quality of coffee beans.

The most common roast flaws in coffee

Mistakes are made on a regular basis. Mistakes are typical in the roasting process since there are so many variables, such as chemistry changes, temperature, time, profile roasting, and so on, to consider. The following are the most often encountered types of slang.

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This is a delicate balance between dark roast and overdeveloped roast. In general, an overdeveloped roast will be dark in color and have a lot of oil on the bean’s surface.

As a result, the flavor will be burnt and smoky, with chemical or pipe tobacco aromas. Tip: Overdeveloped beans can occur in a good roast. Some beans will roast faster than others during the process.

You can remove them when grinding a small amount of coffee; otherwise, they will ruin the taste of the coffee.


Here’s another example of a common blunder. The sugars aren’t caramelized enough, or the CO2 inside the bean isn’t fully developed.

This will give the coffee a “grassy” texture. In addition, you will notice that the crust is unlikely to form while cupping.

The flavor will be similar to hay, grass, oats, corn, lentils, and so on.

This type of error occurs due to a desire to roast lighter. Or the temperature was not properly controlled during the process. Or something went wrong during the process.

These two roast flaws (overdeveloped and underdeveloped) are fairly obvious. One is quite dark, while the other is far too light brown.


This is a roast flaw that is both underdeveloped and burnt. This is due to an overheated drum and slow rotations of the roaster machine.

Aromas and oil will be overheated, resulting in a scorched, grassy, and bitter flavor. The beans will be ashy but underdeveloped.


Here’s a roast flaw that isn’t easily identified. It necessitates a refined sense of taste. This error can be caused by several factors, including too much time between the first crack and insufficient energy in the first place.

The flavor will be baked with hints of yeast or oat. It can also have a sharp or pungent flavor.

This isn’t a roast defect, but you’ll usually notice it after roasting. During the sorting and green bean inspection, there are unripe beans that are difficult to identify. This can be caused by poor soil conditions that limit sugar availability.

The flavor will be dry, papery, acrid, and resinous.

These are the most common roast flaws found in a cup. Some can be caused by using the incorrect profile roast or simply by chance.

How to Detect Defects in Cupping

Cupping is a technique for tasting and evaluating coffee. It is the most effective method for determining roast flaws, bean flaws, and specific notes. So, here’s a quick rundown of roast flaws and how to spot them when cupping.

Overdeveloped – The color of the ground coffee will be too dark, and oil particles will be visible in the crust.

The aromas will be more like those found in the dry distillation zone (carbonyl, spicy, resinous), and the notes will be peppery, piney, smoky, and ashy.

Scorched – Despite the dark color of the beans, the flavor will be distinct from overdeveloped roast flaws. That’s because the beans aren’t fully developed yet, but they’re still burnt.

The color may be similar to the overdeveloped defects, but the crust will be oil-free. As a result, the aromas will be more intense, with clove, thyme, or camphoric taste notes.

Underdeveloped – This roast flaw is not always obvious at first glance. The color may be light brown, but it will still be a good roast.

It is necessary to smell and taste the coffee to identify these beans.

First and foremost, the crust is less likely to form.

Second, the aroma will be more spicy, grassy, or medicinal, with sour, astringent, and sharp notes.

Baked: This roast flaw can be detected solely by taste during cupping. As the notes cool, they lose more of their acridity, sweetness, and flavor warmth. There are also yeasty, baked-like, and raw-like notes.

Quakers: The beans will be lighter in color than the other coffee beans. They are not well developed, resulting in cereal and papery notes with a dry aftertaste.

These are the most common roast flaws that can ruin a cup of coffee. Numerous other factors can degrade the coffee experience, such as bean defects, poor extractions, and so on, but we’ll discuss them in another post.

A bad roast will sour the experience.

A single green bean contains over 1000 different ingredients.

Caffeine is the most prominent component, but carbohydrates, fats, water, proteins, acid, alkaloids (caffeine), minerals, and aromas are important.

Carbohydrates make up the majority of the weight. These are converted into other chemical compounds during the roasting process or completely broken down.

Fats and oils are also important flavoring agents.

Acid also plays an important role in taste. These are formed and, in some cases, destroyed during roasting. The more roasted it is, the more bitter substances are produced.

Overall, these different ingredients can turn a batch into either a great roast or something bitter and harsh with flaws.

It is easy to make mistakes during the process, so roasting is the most important factor in determining coffee quality.

If something goes wrong with the roast, everything goes wrong. The barista will no longer extract the best from the coffee, and the beverages will be subpar.

Furthermore, many people brew coffee at home, and getting a bad cup of coffee can be very frustrating.

Many of them can have a bad roast even if they aren’t aware of it. As a result, everyone must understand the fundamentals of roast defects and identify them through the tasting.

A good roast can bring out the best in people.

Of course, a good roast can provide a pleasant experience for customers. In cups, a good roast can be easily identified. It will have floral or fruit aromas and notes of chocolate, forest fruits, oranges, and so on.

What else can sour a good cup of coffee?

Aside from roast flaws, many other factors can ruin a good cup of coffee, such as natural bean flaws, poor water, and insufficient extractions.

When all of these elements combine in the same cup, the result is a very bad cup of coffee.

A brief examination of the bean flaws

Before roasting, a good roaster will take the time to double-check the beans for flaws.

A large number of roast flaws can occur due to bean flaws. However, because they are fairly easy to identify, you can remove the bad beans before roasting them.

You can also remove them before grinding your coffee if you notice they’re bad and roasted.

Here is a shortlist of bean flaws that can be removed after roasting to improve the overall experience. There are many more, but they are visible before roasting.

Bean shells and broken beans These are not whole beans, but rather a bean with a hole. Although it is a natural flaw, it can ruin a cup of coffee.

In addition, because they are half beans, they typically roast quickly and produce a bitter, harsh flavor with low acidity.

Gnawed beans as a result of insect infestation Coffee beans can be eaten by pests like many other seeds in fruits. This is also a natural process, but it can taste bad bitter. It has the appearance of a normal bean but has very small holes on the surface.

Unfortunately, only these two bean flaws can be discovered after roasting. All other flaws can be fixed right before the roast. However, removing them is still a good idea when making coffee.

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