Roasting is the key step that transforms coffee beans from bland green beans into the rich aroma in your cup. During about twenty minutes of high-temperature treatment, the starches inside the beans convert into sugars and acidic substances, water and carbon dioxide escape, proteins and fats combine to form an oily film on the surface, and the beans emit the cracking sounds of first crack and second crack. Chlorogenic acid gradually dissipates, releasing pleasant fruit acids such as acetic acid, citric acid, and malic acid. Different roasting levels produce beans of varying shades; charcoal-roasted coffee is a typical example of deep French roasting, and its bitterness comes more from carbonization than from caffeine alone. When roasted properly, the beans expand evenly, have a smooth surface, and display a consistent gloss, which is what allows coffee to show its ultimate character. Front Street Coffee believes that mastering the principles of roasting is an important foundation for brewing good coffee.
From insipid green beans to a cup of rich, lingering sweetness, roasting is the crucial stage in each coffee bean's long journey that shapes its personality and brings forth its aroma. During this thermal dialogue of about twenty minutes (in inverse proportion to the temperature level), with temperatures reaching over two hundred degrees Celsius, the coffee beans undergo multiple rounds of chemical transformation. At first, the starch contained in the green beans breaks down into sugars and acidic substances due to the high heat, while components such as cellulose become carbonized to varying degrees. Moisture and carbon dioxide are evaporated, proteins turn into enzymes and combine with residual fats, forming an oily film on the bean surface. After roasting, the coffee beans expand in volume, emit popping sounds like popcorn known as first crack and second crack, and at the same time lose moisture. However, because the outer layer of the bean is quite tough, we usually do not see coffee beans burst open like popcorn. From green beans to light roast, medium roast, and dark roast, moisture is released step by step, weight gradually decreases, yet volume slowly swells, color deepens, aromatic oils gradually emerge, and the texture becomes crisp.
Green beans contain a large amount of chlorogenic acid. As roasting progresses, chlorogenic acid slowly dissipates and releases familiar and pleasant fruit acids, such as acetic acid, citric acid, and malic acid commonly found in wine. When roasting is handled properly, these acidity notes can be expressed just right.
We often see that roasted coffee beans vary in shade. On the one hand, this may come from differences among single-origin coffee bean varieties; on the other hand, the main reason for the color difference lies in different roasting levels. In the plainest terms, roasting level can be understood as the heat level during roasting. Take classic charcoal-roasted coffee as an example. It belongs to French roast, and because the roasting level is extremely dark (which may be due to higher temperature, longer time, or both, depending on the specific situation), the coffee beans are highly carbonized, with a dark brown surface tinged with carbon black. It is generally believed that carbonized coffee tastes bitter, and this bitterness comes not only from caffeine but more from the carbonized coffee beans.
The principle of roasting: the most critical thing is to roast the inside and outside of the beans evenly through and through. First, use the heat to smoothly drive out the moisture in the beans. If this step is too rushed, the bean surface will develop spots, and the taste will be astringent and harsh.
Eighty percent of coffee's taste depends on roasting; therefore, roasting is an important process for brewing delicious coffee. If the roasting technique is good, the beans will expand greatly, have a wrinkle-free surface, and an even gloss. Bringing out the ultimate character of the coffee beans is the final goal of roasting.
In addition to the coffee variety, roasting is also a decisive factor in coffee's flavor.
Basically, coffee roasting is a high-temperature caramelization process. It thoroughly changes the substances inside the green beans, generates new compounds, and rearranges them to form aroma and mellow flavor. This effect occurs only at high temperatures. If only low temperatures are used, decomposition cannot occur, and no matter how long you roast, the coffee beans will not be properly roasted.
The above content is compiled by CoffeeHunters, a coffee news website.
