Fermentation processes involve microbial complexes in which yeasts and lactic acid bacteria are the microorganisms that interest us the most.
They act by degrading sugars and converting them into alcohol, organic acids such as acetic and lactic acid and CO2. In this process, temperature plays a very important role.
In general, when a fermentation process occurs in uncontrolled environmental conditions, it starts at room temperature. As the hours go by, the temperature increases while the microorganisms degrade the sugars.
The microbial populations change in such a way that they overlap in time. Each population will act within a specific temperature range and on specific types of compounds, generating different kinds of by-products.
These by-products of microbial biosynthesis are precursors of volatile aromatic compounds that will ultimately be responsible for giving coffee its acidity, body, flavor and aroma characteristics.
The wine industry has studied for years the fermentation processes and the way in which temperature can be controlled in order to obtain characteristic and desirable flavors and aromas.
Temperature affects the sensory profile of fermented beverages
In the wine industry, it has been found that when fermentation occurs at a temperature of 15°C, the formation of volatile compounds associated with fresh and fruity aromas is promoted. At 28°C, floral and tropical fruit aromas such as banana and pineapple are accentuated instead.
Therefore, more attention was placed into the selection of yeast strains adapted to lower temperature ranges between 13 and 15°C.
This allows wine producers to create wine profiles according to consumer preferences by controlling fermentation temperatures and the microbial strains involved in each phase of the process.
In the case of coffee, work has also begun in this direction, hence the importance of controlled fermentation processes.
As with wine, in coffee it has been demonstrated that the optimum temperature for yeasts to metabolize the sugars in the mucilage is between 30 and 40°C (86 and 104°F).
But when fermentation occurs at lower temperatures, the amount of acetic acid produced decreases, and cleaner flavors, complex acidity and fruity and floral profiles are obtained. Higher temperatures develop exotic tropical fruit flavors and tartaric acidity.
All this work done in the field of wine fermentation has led to experimentation with thermal shock, after which it is possible to carry out coffee fermentation at low temperature with the inoculation of selected microbial strains.
This avoids the formation of acetic acid and favors the formation of desirable flavor and aroma precursors that are not formed during a conventional fermentation process.