The group of the Center of Excellence in Coffee at the University of Applied Sciences in Zurich has been at the forefront of studies on the freshness of coffee for a decade.
What’s Freshness of Roasted Coffee
The definition of coffee freshness is to have unfounded original qualities. Specifically, we are talking about the freshness of roasted coffee. The reason for this is that roasting generates the aroma of the coffee, making the beans be extracted but also making the coffee unstable. Only after roasting can coffee beans allow oxygen to affect the beans, and the labile aroma of the coffee easily escapes the beans. Roasted coffee is therefore unstable, the material constantly changing. To understand the freshness of coffee, we must first understand why and how freshness is lost.
There are four most important external factors that are involved in the loss of freshness:
1 – Space
Freshly roasted coffee beans are saturated with volatile flavor molecules. Due to the physicochemical forces, the aroma will want to escape in any open space available around the grains.
2 – Oxygen
Contact of coffee beans with oxygen in the air can cause degradation of some of the sensitive components of the flavor. This degradation can be perceived, but in many cases, the loss of flavor is dominated by the flavoring process that escapes into the open space around the bean. However, another oxidation, the oxidation of coffee oil, produces very unpleasant rancid tasting components that should be avoided in any coffee. The oil is naturally present in roasted coffee beans, and the oxidation in the beans can be quite slow. But in the case of oil migration to the grain surface, the effects are fast and very unpleasant.
3 – Temperature
In both processes mentioned above, aroma diffusion and oxidation are dictated by temperature. Temperature determines the movement of molecules and the hotter it is, the faster it moves. When it moves fast, it becomes more and more likely that the aroma gets rid of the beans and that the oxygen causes damage to the grain. Theoretically, if we cooled the coffee to absolute zero temperature, we would keep it fresh indefinitely.
4 – Time
None of the processes of losing freshness are instantaneous, they all need some time to happen.
The four factors mentioned are important to understand the processes behind the freshness of coffee and why it is such a sensitive product. They are not the only factors that can destroy the aroma of the coffee, for example, humidity or strong light can also destroy the qualities of coffee. It has been found that higher moisture in ground coffee increases the rate of release of flavor loss from coffee.
Taste is, of course, the most important attribute of coffee, but when we look at the whole picture of freshness, it is not the only thing we need to be aware of. The freshness of coffee is very complex and when we talk about the freshness of coffee, there are two different types of freshness ”that we recognize: chemical freshness and physical freshness.