No one will achieve a perfect roast on their first try, or on their second, or even on their tenth. It takes experience and more than a few burnt beans to understand and control the roast profile. But it is much easier to do so when you understand what roasting defects you are experiencing.
Baked bean
This defect occurs when the coffee is heated for too long without reaching the first crack. It can also be called “over-roasting”. When the temperature is too low, the roasting process lasts longer than necessary, which prevents the bean from reaching its full aromatic potential and, as a result, it does not undergo the proper chemical and physical changes to fully develop.
Unfortunately, this defect cannot be detected visually; however, it can be clearly identified during the cupping phase. The cup is characterised by a flat taste with a small amount of sweetness, often described as bread-like or paper-like.
Underdeveloped beans
Underdevelopment is most commonly seen in light roasts when the roasting process was stopped too early. Sometimes the beans look roasted outside but are still underdeveloped inside because the internal temperature did not have time to rise sufficiently before the roasting was finished.
Underdeveloped beans tend to be “grassy” and lack the caramelised sugars that appear during roasting. Underdeveloped coffee contains more citric acidity and lacks sweetness and body. This usually means that it will have a higher acidity in the cup, but due to the lack of body, it will seem watery.
Scorched bean
Scorching is a roasting defect that occurs when coffee is in contact with the hot walls of the drum for too long for several reasons: too high drum speed creates a centrifugal effect, similar to that of a washing machine, that presses the beans against the walls. Or, due to an overload of coffee in the drum, it prevents the coffee beans from moving in a constant and even manner.
The so-called “burns” can be seen as small brown or black spots on the surface of the bean before the first crack.
Scorched coffee gives the cup a bitter, ashy and smoky taste.
Tipped bean
This type of defect can be similar to that of scorching, but the main difference is that the air burn marks are on the edges of the bean, not on the bean walls, as is the case with scorching.
There are several possible explanations for this defect. Some believe that it is caused by a high initial temperature, but others blame it on deformed or oddly shaped beans or problems with air flow inside the roaster.
Coffee made from air-burnt beans has a harsh, smoky aroma and flavour.
Overdeveloped (burnt) beans
Overdevelopment occurs when coffee beans are roasted for too long. It is most common when trying to achieve a dark roast.
Overdeveloped beans will have a smoky and ashy flavour and will be extremely dark and oily. Some overdeveloped beans will have a burnt and bitter taste, regardless of how they are prepared. However, bitter coffee is not always a roasting defect, and a bitter taste can be a sign of over-extraction during brewing.
Without a doubt, a clear roasting procedure will help you to improve the quality consistency of your roasted coffee. In addition to checking the quality profile of the roasted beans, it is recommended to document the target flavour profile for each type of coffee, which should be compared to the current roasting results using cupping protocols. For example, after each roasting session, the operator should taste at least 2 cups from each roasted batch and compare the intensity of the key parameters of the coffee flavour profile (acidity, body, sweetness) to the target level. This allows you to effectively evaluate your own progress, which improves roasting consistency and ultimately increases customer satisfaction.
