This rapprochement has been reflected in a number of published studies in recent years, with the participation of the 220GRAD roastery. This culminated in this year's ALIMENTARIUS Price 2022.
“…Coffee beans are not a homogeneous entity, but as a heterogeneous solid with a eukaryotic cell structure, they also contain liquids and gases, which undergo physical and chemical changes during roasting. Additionally, the pressure within the coffee beans is also subject to dynamic changes due to heating and the rupture of the beans, which affects the boiling points of the liquids within the cell structures.
Temperature thus loses its significance. Because temperature is, after all, what it is: a human-created description of a state – which, when used judiciously, can provide valuable information. When monitoring the roasting process, temperature can therefore only provide information about the progress of the roasting in relation to the roasting machine used and the batch size.
The first phase of roasting, the drying phase, can serve as an example. The original water content of 10-12% in green coffee is largely removed from the beans through evaporation at the surface during the first phase of roasting using energy (heated airflow). With rapid roasting profiles, this occurs at the point…” The yellowing (green -> yellow) of the bean occurs at higher temperatures but for a shorter duration. With slower roasting profiles, the yellowing reverses at lower temperatures but with a longer drying phase. The specific amount of water that inhibits the Maillard, Strecker, and other reactions is therefore already present in the bean with a slower roasting profile before the higher temperature of the faster profile is reached. Faster profiles also tend to result in more uneven roast levels, as the energy level of the bean's center always lags behind that of the surface (Fig. 1). Therefore, charring processes with accompanying "burnt" odors always occur first at the outer edges of the elliptical beans during very advanced roasting.

Fig. 1: The heat distribution and drying in the bean is dynamic, involving gas evolution, pressure increase, convective energy transfer at the surface through the heated airflow, and conductive energy transfer through the internal solid bean structure;
Additionally, the density and size of the green coffee beans play a crucial role. This means that the sugars and amino acids present are converted into different end products in different roasting profiles and/or batch sizes due to the resulting differences in reaction kinetics. Temperature measurement cannot provide this information. […] Therefore, this doctoral thesis has laid the foundations for so-called “chemical monitoring.” This means that the actual chemical changes on the bean are to be recorded online. The precise technical implementation is still a long way off. Why is a new measurement method so urgently needed? There is one key word here: climate change […]. In addition, the traditional heating source, natural gas, will increasingly give way to electricity and hydrogen. Energy from these sources behaves differently when transferred to the beans – here, too, temperature has only a marginal informational value….” (Source: Magazine ERNÄHRUNG)
Thus, at 220GRAD, we no longer understand roasting temperature in this sense – but rather a kind of interested and open approach and a humble attitude towards our own knowledge and skills, which are constantly being updated. Coffee is the perfect vehicle for this: behind every insight, be it about green coffee, roasting, or extraction and preparation, three more questions await. So we continue our exploration with great confidence and often derive more pleasure from the questions than from the answers.
Original article
"Who, How, What...?" | How, Why, What... Tohese who do not ask remain in the dark."