What Causes Uneven Coffee Bean Roast Colors? Why Do Light Roast Coffee Beans Have Color Variations?

Have you ever encountered this situation? You buy a new bag of coffee beans, full of anticipation as you open the package, only to discover that the beans inside have uneven coloring - some lighter, some darker. At this moment, you might think, "I've made a bad purchase," "This shop's quality control is terrible," or "This shop's roasting is really poor."

I believe that in many people's minds, excellent coffee beans should appear plump, uniform in size, and have very consistent coloring after roasting.

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We must be clear about one thing: coffee beans are agricultural products, and it's impossible for every bean to look identical like industrial products. For example, friends often report that the coffee beans they purchase vary greatly in size. This friend most likely purchased Ethiopian coffee beans.

Ethiopia's grading system for green coffee beans is based on defect rates - the fewer defects in the green beans, the higher the grade. The size of coffee beans is not a factor in determining grades, which is why we often see both very large and very small beans in Ethiopian coffee.

When purchasing coffee beans, some friends might ask, "What grade is this bean (G1, G2, etc.)?" or "Is this coffee bean really G1?" In reality, these grades refer to the green bean level and primarily serve as a basis for pricing negotiations among green bean traders. Take Ethiopian beans as an example - whether G1 or G2 grade, after multiple rounds of selection before reaching the end market, their quality reaches very similar levels.

Moreover, if lower-grade coffee beans are used in roasting, it means spending more energy and time to sort out defective beans. In such cases, roasters prefer to choose higher-grade beans (sorting beans is truly torturous). Furthermore, the quality and price differences between high-grade and low-grade green beans aren't as significant as people might imagine.

Understanding Uneven Coffee Bean Colors

When roasted coffee beans show uneven coloring with distinct light and dark patches, people often assume this is caused by roasting accidents. This color unevenness most commonly occurs in Costa Rican coffee beans.

It's not that Costa Rican coffee beans are of poor quality or particularly difficult to roast. Rather, most Costa Rican coffee beans are processed using the honey method.

Honey processing falls between natural and washed processing. First, the coffee cherry skin and some pulp are removed, then the remaining beans with their mucilage are placed on drying beds. The sugars in this mucilage adhere to the coffee bean surface as water evaporates. Therefore, even at the green bean stage, honey-processed coffee beans show varying surface colors - the more mucilage retained, the more obvious the color difference.

During roasting, beans with more sugar on their surface undergo more pronounced caramelization, resulting in darker colors, while beans with less surface sugar appear lighter. This contrast between dark and light makes the color difference particularly noticeable.

In fact, if the coffee beans were roasted darker, the colors would become more uniform. However, this would make the flavor more bitter. For example, the Sherry coffee beans used by FrontStreet Coffee for pour-over differ in roast level from those used in the Warm Sun blend for espresso. The lighter-roasted pour-over Sherry shows more color variation than the darker-roasted Warm Sun Sherry. In terms of visual appeal, Warm Sun Sherry might look more pleasing, but in terms of pour-over flavor, the pour-over Sherry tastes better.

Understanding White Beans and Other Misconceptions

Not only Costa Rican honey-processed coffee beans show this characteristic, but some coffee beans with strong anaerobic fermentation also display very obvious color differences after roasting. This is not improper roasting or defective beans and doesn't affect the coffee's flavor.

Here, I should specifically mention that when FrontStreet Coffee previously shared knowledge about defective beans, we mentioned one type that isn't obvious in its green state but appears very light in color after roasting. This defective bean is called a white bean. I suspect many friends, seeing light and dark colored coffee beans, have hastily judged the lighter ones as white beans.

This judgment isn't accurate. White beans come from unripe coffee cherries. After removing the skin, these green beans are difficult to distinguish from normal ones, but their color change is particularly obvious after roasting. White beans appear light brown and smell like roasted sunflower seeds, underripe, and green. They typically appear more frequently in mechanically harvested coffee like Brazilian beans; they rarely appear in hand-picked coffee that emphasizes fully ripe cherries (you might find 1-2 beans in 3kg of green beans). Therefore, when you find many very light-colored coffee beans, you can be assured they are definitely not white beans.

PS: It's precisely because Brazilian beans contain many white beans that significant time is spent sorting these defects after roasting. Therefore, when you open a bag of Brazilian coffee beans and see uniformly colored beans, it's the result of roasters implementing strict quality control.

Other Bean Characteristics Often Mistaken for Defects

Besides these situations, there are other coffee bean characteristics that are often mistaken for defects or roasting accidents...

First: Obvious wrinkles and black spots

This appearance typically occurs in high-altitude, lightly roasted washed coffee beans. High-altitude beans have high density. During roasting, as moisture evaporates, they shrink and develop wrinkles. Because of the light roast, the beans are removed from the roaster before they have fully expanded. Although these beans might look wrinkled and unattractive, I can confirm 100% that they are not defective beans, and their flavor profile exhibits very pleasant acidity.

Second: Split beans

Some coffee beans split open during roasting, looking incomplete and easily mistaken for defective beans. In reality, these are also normal coffee beans. It's because the beans have high density and absorb significant heat during roasting, leading to vigorous cracking at first crack that splits them open. Although they don't look aesthetically pleasing, they don't affect coffee flavor and may even make the coffee taste better.

Third: Unique appearance

Some coffee beans are very conspicuous because they look different from other coffee beans. Many people assume that different appearance must affect coffee flavor. In reality, these aren't defective beans - they just have unique personalities. Of course, if their appearance bothers you, you can treat them as defective beans.

Important Notice :

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

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