Fact check: Roasting date

Is fresher always automatically better? A few reasons against it.

Faktencheck: Röstdatum

Roasted coffee is a fresh product. But how do we define freshness, and what does that mean for everyday life?

In science, there is a defined index based on the ratio of the aroma molecules dimethyl sulfide and methanethiol. Dimethyl sulfide is formed from methanethiol through oxidation (in this case, reaction with oxygen in the ambient air). Dimethyl sulfide levels increase over time, while methanethiol levels decrease. However, this is of little practical use.

A much more visible indicator is the carbon dioxide (CO2) content in the coffee bean. Espresso made from very freshly roasted coffee beans develops a richer crema layer than espresso made from older beans. CO2 is produced during the roasting process, firstly through the so-called Strecker degradation of amino acids to aldehydes (e.g., methylbutanal: malty, sweetish), and later in the process, to a greater extent, through the pyrolysis of larger carbohydrates in the coffee bean. This means that darker roasts produce significantly more CO2 in the bean than lighter ones. This should be taken into account when assessing the freshness of coffee beans.

So when is the right time to use coffee beans for espresso extraction? Generally, beans from darker roasts are truly suitable for extraction starting about three weeks after roasting. After approximately five weeks, they reach their peak in terms of crema formation, aroma intensity, and extraction efficiency. During this time, the espressos are beautifully balanced. With proper storage, beans can be used for up to three months after roasting and still produce excellent results. Using the beans shortly after roasting will result in an overly effervescent espresso, meaning the crema formation is very intense due to the high CO2 content.
The high CO2 concentration in the bean, however, also reduces extraction efficiency. The water cannot sufficiently dissolve the aromas and other desired substances. The aroma intensity in the extract is therefore significantly better a few weeks after roasting. Furthermore, it is assumed that the high CO2 content acidifies the extract. This is because the CO2 is released from the coffee grounds as carbonic acid; some of it evaporates again in the crema as gas bubbles, while some remains as carbonic acid in the extract. The degassing of the coffee beans over the weeks following roasting thus brings more balance to the cup, resulting in a "softer" and more rounded flavor. With 100% Robusta beans, it is even worthwhile waiting up to two months before opening the package. Robusta beans produce more CO2 during roasting due to their different chemical composition with regard to carbohydrates and amino acids. For lighter filter roasts, there is less "interfering" CO2 present for extraction; however, lighter beans degas much more slowly than darker roasts. Due to their roast level, lighter beans have lower internal porosity, meaning the gas and aroma molecules migrate to the surface of the bean much more slowly. In practice, this means you can easily wait up to six weeks after roasting before opening the package. Coffee is a fresh product; coffee is a dynamic product. Those who only judge the crema are merely scratching the surface. The true treasures lie in the depths of the cup.

Summary:

  • Time window for espresso: 3-6 weeks after roasting, max. 3 months
  • Time window for 100% Robusta espresso: 2 to 5 months after roasting
  • Time window for lighter roasts in filter preparations: 5 to 12 weeks after roasting.
  • Dark roasts "age" faster than lighter roasts.

 

Original article

"Fact check: Roasting date" | Is fresher automatically always better? A few reasons why not.