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Coffee Roasting Defects

Known as “roast defects”, these mistakes typically occur when roasters lack information on what’s going on during key points of the roast. 

Identifying these defects and taking measures to prevent them from happening is essential for roasters who want to create consistently high-quality coffee for consumers.  

Scorching

Scoring happens with a combination or one of the following, “charge temperature” and or “drum speed”. If your initial temperature is too high you will scorch the beans and this would appear as dark burnt spots on the flat surfaces of the beans. Sometimes and especially your higher grown beans need a very high charge to build up the required energy you need to start the roast, the only change you would need to make is up the drum speed. The increase in drum speed would reduce contact and help prevent surface scorching. Be careful that you don’t adjust this too much as this could lead to other issues. Dark roasted coffee is not scorched coffee, it may appear similar but on closer inspection, you will see the difference.

Tipping and scorching look similar but the main difference is that the marks are on the edges of the beans and not on the flat surface.

Tipping

Tipping can take place also due to a high charge temperature or the incorrect drum speed but this could also take place after first and second crack. The beans are a lot lighter in weight and also because of a slightly large edge, tipping happens easier. Once again watch your beans closely during your Roast and make the necessary adjustments to compensate for the challenges that you may be having.

Underdevelopment

Underdevelopment generally occurs when a bean has not been roasted enough, or not roasted thoroughly. Using the guidelines in the previous tutorials/videos will help prevent this. Depending on the roast profile you are intended to roast to ensure that each phase/stage of the roast has occurred correctly and sufficiently. Underdevelopment can also generally occur if you stall the roast which could also end up leading to baking the coffee. Ensure you keep sufficient and controlled energy and this will help prevent underdevelopment from happening. On the outside, the bean may appear slightly lighter than normal and that bean will most likely be far denser and the moisture content will be higher too. Upon proper evaluation with breaking or grinding the beans, there would be an uneven roast and if you check with a moisture meter this would confirm that too. The key with this is cupping the coffee and checking it. The taste on the table will confirm this with possibly grassy or grassy-like flavours.

Check your graphs and make the necessary changes.

Overdevelopment

Overdevelopment is a tricky one as there are many trains of thought when it comes to this. If you stagnate a roast and you continue to roast the coffee, your graph will show coffee with a very high percentage development, and this could lead to a very bitter, toasty flavoured coffee with a complete lack of complexity. Another view would be that the coffee would be over roasted or dark. This would lead to a very different taste and result, but it all depends, once again, on what you are trying to achieve in your Roast. Development can be a tricky thing as it boils down to what are you trying to achieve from that specific batch you are roasting? What brew method will it be used for? What flavour profile are you trying to achieve from that specific coffee, especially if it’s a higher-grade specialty?
 

Baked coffee

This can also be directly related with underdevelopment or overdevelopment. Generally baked coffee occurs when you don’t have enough energy in your Roast and your Roasts end up being extremely long. Coffee that is baked can taste dull, even bready or grainy. Baking coffee will generally take place in the second or third stage of Roasting. The starting phase of your roast is vitally important when you still have the ability to control and make the necessary changes that are needed to fix the roast. Generally, beans will end up extremely hard and your roast would have been a longer time than usual. Remember the four main factors of roasting: charge temperature, gas/energy, airflow and drum speed. If these factors are perfectly aligned you should not experience baked coffee issues.
 


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