Why are coffee beans roasted?
In this text we will answer the question: “Why are coffee beans roasted?”. In addition, we will talk a little about the coffee roasting process and what is the best type of coffee to buy, in roasted or powdered beans.
Why are coffee beans roasted?
Roasting plays a key role in determining the quality of coffee beverages. When green coffee beans undergo the roasting process, they undergo intricate physical and chemical transformations.
The physical changes are readily noticeable in the significant alterations in the shape, water content, density, color, and internal structure of the beans.
Meanwhile, the chemical changes are characterized by the occurrence of the Maillard reaction and caramelization reaction, which generate both pleasant and unpleasant compounds that directly influence the overall beverage quality. (1)
What other process can roasted beans undergo?
After coffee beans are fully roasted, they can undergo the process of grinding. This step is essential to enhance the specific surface area of the beans, facilitating the transfer of soluble and emulsifiable compounds from the coffee matrix to water during the brewing process.
Grinding increases the contact between the coffee particles and water, enabling a more efficient extraction of flavors and substances from the beans. (2)
How is coffee roasting performed?
This process, which lasts from seven to fifteen minutes and varies the temperature of the beans from 150°C to 230° C. The process is usually characterized by the following consecutive stages:
– Temperature increase from ambient to about 150 ºC
As the roasting process unfolds, the temperature of the coffee beans gradually rises until it reaches the point where the water content within the beans evaporates.
Initially, the vapor generated cannot escape, causing an increase in pressure that leads to the expansion of the bean’s volume.
Once the pressure reaches a critical point, the outer shell of the bean cracks open. This phase marks a significant transformation as the bean’s color transitions from green to yellow, and the aroma begins to develop. (1, 2)
– Temperature from 150 to 180 ºC
Color changes from light yellow to brown, primarily due to the development of non-enzymatic browning reactions. These reactions penetrate the inner, drier structure of the beans.
As a result, the beans become more brittle, and small fissures may appear on the surface. This phase also marks the initiation of aroma formation.
The sugars present in the beans, particularly sucrose, undergo caramelization, contributing to the development of flavors. Additionally, the roasting process leads to an increase in acidity as carboxylic acids are formed through the degradation of carbohydrates. (1, 2)
– Temperature from 180 to 230 ºC or more
As the roasting progresses, the color of coffee beans deepens, and they expand due to the build-up of high internal pressure caused by water vapor, CO2, and volatile compounds generated as a result of the Maillard reaction.
The release of these substances leads to weight loss and the rupture of the bean’s internal structure. Additionally, pyrolysis and caramelization occur during this stage.
Caramelization contributes to the development of pleasant flavors and sweetness. Furthermore, the acidity of the beans decreases as a result of acid degradation. (1, 2)
– Temperature decrease
In order to halt the roasting process and prevent the coffee beans from burning, the hot beans are rapidly cooled down using either water quenching or air cooling methods.
This cooling process continues until the beans reach the ambient room temperature, effectively putting a stop to the roasting and preserving the desired level of roast for the coffee. (1, 2)
Coffee beans contain approximately 43% carbohydrates, 7.5-10% proteins, various nitrogenous compounds (including 0.6% – 2.8% caffeine), 10-15% lipids, 25% melanoidins, 3.7-5% minerals, and around 6% organic and inorganic acids and esters.
During the roasting process, there is no significant loss of caffeine, and in fact, its concentration increases due to the degradation of other components. (3-5)
What are the health benefits of coffee beans?
Caffeine, a natural stimulant, exerts its effects on the brain and central nervous system, providing various benefits such as increased energy, heightened alertness, improved mood, enhanced memory, and overall better performance.
Furthermore, caffeine has the potential to improve exercise performance and aid in weight loss by boosting metabolism (5).
Coffee beans, known for their richness in antioxidants, particularly contain a significant amount of chlorogenic acid. This compound has shown promising effects in reducing the risk of diabetes, combating inflammation, and even exhibiting anti-cancer properties.
The concentration of chlorogenic acid in coffee beans may vary based on factors such as the bean variety and specific roasting techniques employed.
During the roasting process, there is a reduction of 50-95 percent in the content of chlorogenic acid. Nevertheless, coffee beans are still highly regarded as an excellent source of this beneficial compound. (6, 7)
How to store coffee beans?
It is recommended to preserve coffee beans in an air-tight container, or if unopened, in their original packaging, store the container in a dry and cool place, away from direct sunlight and heat sources.
Additionally, it is advisable to use an opaque container, as this shields the beans from light exposure, which can negatively affect their quality.Furthermore, after opening the container, ensure that you tightly close the cap or lid.
Failing to do so can allow air and humidity to enter, creating an environment favorable for the growth of bacteria and mold. This can shorten the shelf life of the coffee beans, ultimately requiring you to discard them. (2)
Other FAQs about Coffee that you may be interested in.
In this text we answer the question: “Why are coffee beans roasted?”. In addition, we talk a little about the coffee roasting process and the best type of coffee to buy, in roasted or powdered beans.
- Hu, G., Peng, X., Gao, Y., Huang, Y., Li, X., Su, H., & Qiu, M. Effect of roasting degree of coffee beans on sensory evaluation: Research from the perspective of major chemical ingredients. Food Chemistry, 331, 127329. 2020.
- Manzocco, L., Melchior, S., Calligaris, S., & Nicoli, M. C. Packaging and the Shelf Life of Coffee. Reference Module in Food Science. 2019.
- Caroline Woelffel Silva, Keila Rodrigues Zanardi, et. al. Green coffee extract (Coffea canephora) improved the intestinal barrier and slowed colorectal cancer progression and its associated inflammation in rats, PharmaNutrition, 22, 2022.
- Farah, Adriana. Nutritional and health effects of coffee. 10.19103/AS.2017.0022.14. 2018.
- Mary Jane Brown, Can You Eat Coffee Beans? All You Need to Know. Them. Healthline Media LLC. 2020
- Wei, F., Furihata, K., Hu, F., Miyakawa, T., & Tanokura, M. Complex mixture analysis of organic compounds in green coffee bean extract by two-dimensional NMR spectroscopy. Magnetic Resonance in Chemistry, 48(11), 857–865. 2010.
- Tajik, N., Tajik, M., Mack, I. et al. The potential effects of chlorogenic acid, the main phenolic components in coffee, on health: a comprehensive review of the literature. Eur J Nutr 56, 2215–2244. 2017.