What Are Coffee Roasting Defects | Characteristics of Roasting Defects | How to Identify Roasting Defects

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When we think of coffee defects, we usually consider either defective beans being mixed in or problems with brewing. However, there's another situation: roasting defects! What exactly are roasting defects? FrontStreet Coffee is here to explain them to you!

Roasting beans is a technical skill. No one achieves perfect coffee roasting on their first, second, or even tenth attempt. It requires professional knowledge and accumulation of various abnormal situations to better understand and control your roasting curve. However, when you understand the problems that occur and their underlying causes, roasting becomes much easier.

1｜BAKED COFFEE

Excessive roasting time before the first crack is the main cause of baked coffee. Unfortunately, this defect isn't visible to the naked eye and can only be identified through tasting. Typically, baked coffee is accompanied by flat flavors lacking sweetness, described as bread-like or papery tastes.

2｜UNDER DEVELOPMENT

Underdeveloped beans often have a "grassy" flavor and lack caramel aromatics. This sometimes happens when roasters aim for a light roast. At this point, the roaster needs to slightly adjust the roasting curve.

3｜OVER DEVELOPMENT

The opposite of underdevelopment is overdevelopment. There's only a subtle difference between "dark roast" and "overdevelopment." Matt Perger believes there's really no such thing as "overdevelopment."

However, roasting darker than intended is still an error, creating flavors that many professional consumers dislike. These coffee beans appear black and oily, sometimes even charred. Cupping will reveal burnt, bitter tastes with smoky and peaty notes.

* Black beans are just one form of overdevelopment

4｜QUAKER BEANS

Quakers are essentially unripe coffee beans that are difficult to identify during manual sorting of green beans. They are usually caused by poor soil conditions that limit sugar and starch accumulation during growth. Technically, this isn't a roasting defect, but quakers are typically only discovered in roasted coffee beans.

Quakers are lighter in color than other beans from the same roast batch. If not removed, they will contribute dry, papery, and grainy cupping flavors.

5｜SCORCHING

Scorching occurs when the roaster's drum temperature is too high and the rotation speed is too slow. Scorched beans are very easy to identify. Dark, burnt patches appear on the flat surfaces of the coffee beans—essentially the entire bean is burnt. These coffee beans taste distinctly oily, smoky, and even like burnt meat.

6｜TIPPING

Tipping is similar to scorching, but the main difference is that the burn marks are primarily on the edges of the coffee beans. This usually occurs during the second crack, though some suggest that excessively high drum temperatures can also cause tipping.

How to Identify and Prevent Roasting Defects?

Roasters can use professional equipment as aids, such as coffee roast analyzers. These devices cannot prevent defects from occurring, but they help measure roasting consistency.

When roasting, use "quality control charts" to record the different physical changes experienced during the coffee roasting process. Simultaneously, recording the Rate of Rise (ROR) will help understand the development changes in coffee beans, thereby facilitating timely adjustments to prevent defects.

Furthermore, these basic information records help find the most suitable roasting curve for each coffee bean. Roasting should never be judged or decided based solely on color. From appearance, two beans might have the same color, but the curves that produced this color are different, which will determine the final cupping flavors.

What are Roasting Defects?

First: Under-baking (the center of the bean isn't fully roasted) or can be understood as inconsistent roasting levels between the interior and exterior of the coffee bean. When this defect occurs in light roasts, the drinking experience is: 1) weak (the internal roasting level of the coffee bean hasn't reached expectations, insufficient soluble substances have been converted) 2) strong grassy/plant taste (easy to understand - what does eating raw meat feel like?). I haven't tried under-baked dark roasts yet (because I mostly do light roasts).

Second: Scorching (the heat is too intense for the beans to handle): This can be seen from the appearance of the beans:

1. Small black scorch marks at both ends of the beans (note: sometimes the small black spots at both ends aren't necessarily from excessive heat scorching, but could be moldy raw beans, as raw bean defects often occur at both ends of coffee beans).

2. Large-scale scorching on the bean surface.

3. The entire bean is scorched! Coffee with these types of defects generally has a persistent and obvious bitterness in the throat.

Third: Smoke intrusion (drum roasting), where the damper control isn't properly managed during roasting. Smoke intrusion at different stages manifests as different off-flavors. Here's a brief explanation: smoke intrusion in the early roasting stage gives coffee obvious salty and astringent tastes. Smoke intrusion in the later roasting stage makes coffee exhibit smoky and bitter flavors.

Fourth: Uneven roasting levels. There are many reasons for this defect, possibly:

1. Problems with the roaster's agitator blade design.

2. Too few beans being roasted.

3. Still excessive heat intensity.

Important Notice :

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