What Happens During Coffee Roasting? How Heat Transforms Coffee Beans
Coffee roasting in essence is the transfer of heat over time. The heat transforms the coffee beans from their green, raw state into the aromatic, flavorful beans we all know and love. A coffee roaster’s main task is to fully understand what happens during coffee roasting, and how to manipulate the roaster machine to achieve the desired flavor profile of their coffee beans. In order to work more efficiently and produce better-quality roasted coffee beans, coffee roasters need to master the science and art behind the heat transfer process in coffee roasting.
What Happens During Coffee Roasting?
During the coffee roasting process, there are two main changes that happen to the coffee beans: the chemical changes and the physical changes.
The most obvious physical change in the coffee beans during the roasting process is perhaps the change in color. When sugars and amino acids combine under heat, melanoidin polymers form and change the coffee bean to brown. Chaff, or the outer layer of skin, also comes off during roasting. In addition, the coffee beans also undergo changes in moisture level and mass, as the water content is vaporized during roasting, causing the beans to lose 10-12% of their overall weight. The roasting process also makes the coffee beans less dense, more porous, and more soluble.
The chemical changes during coffee roasting are less conspicuous, however, when we introduce the green coffee beans to the heat inside the coffee roaster machine, a number of different chemical reactions start happening. Some chemical compounds inside the beans are degraded, some are altered, and some new ones are created, all contributing to the coffee’s final flavor and aroma. The most well-known chemical changes during coffee roasting are the Maillard reaction, caramelization, pyrolysis, and dehydration.
By understanding both the physical and chemical changes that take place inside the coffee roaster machine, we can appreciate the science and art of coffee roasting and improve our roasting skills.
Unlocking the Flavor Profile
Every coffee roaster has their own style and philosophy, but each has the same goal: to bring each batch of green coffee beans through the coffee roasting process that produces the best cup of coffee. Aside from the quality and origin of the green coffee beans, a coffee roaster’s skills and techniques make the roast unique. The roasting process brings out the flavors of the green coffee beans, by heating the beans so they dry out and the starches are converted into sugars.
The coffee roasting process can be divided into the following stages:
- Drying phase
- Browning phase
- First crack
- Development phase
- Second crack
During different stages of the coffee roasting process, more flavors are developed, with the majority of it taking place during the browning phase due to the Maillard reaction.
In addition, the coffee roaster also seeks to balance the acidity, sweetness, and bitterness in their coffee. This balance depends on the degree of roast, which in turn also depends on time and temperature. Light roasts keep the coffee beans’ natural acidity, which results in a brighter and more vibrant flavor profile. In medium roasts, the acidity level reduces, and the caramelization of sugar increases, which gives sweetness and spice notes. In dark roasts, the beans have a dark oily sheen with a bitter chocolatey flavor.
Practical Tips for Coffee Roasters
Know your beans. High quality green coffee beans are essential for a successful roasting, and a coffee roaster should be very familiar with the characteristics of their coffee beans.
Know your equipment. Berto roaster machines are equipped with state-of-the-art technology that allows precise control over the roasting process in order to achieve consistency and superior quality in every batch.
Know your roast profile. The coffee roaster sets the time and temperature parameters to highlight the unique characteristics of the roasted coffee beans. It is recommended to experiment with different roast profiles to achieve the desired balance of acidity, sweetness, and aroma.
Roasting coffee may look simple on the surface, but many physical and chemical changes are taking place inside the coffee beans, working towards the distinct flavors and aroma. A skilled coffee roaster understands what happens during coffee roasting and can navigate the roasting process smoothly, making tweaks and adjustments based on the beans’ origins and characteristics as well as what the roaster machine is capable of, to achieve the desired flavor profile. Constant improvement of knowledge, skills, and precision is the key.
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