Mass Transfer Kinetics of Nonvolatile Compounds into Coffee Beans during Wet Processing: Study at the Laboratory Scale and in Real Conditions Using Two Yeast Strains

Abstract

The transfer kinetics of four labeled aroma precursors were studied from a liquid medium into the coffee beans during a simulated wet treatment using four media (compositions of M1: dehulled beans, M2: demucilaged beans, M3: depulped beans, and M4: depulped beans with yeast) and then verified via fermentations in real conditions using two strains of Saccharomyces cerevisiae yeast (LSCC2 and LSCC3). Lactic acid, alanine, and glutamic acid were transferred continuously in M1 media, reaching, respectively, 4.8 ± 0.43, 6.4 ± 0.63, and 4.1 ± 0.34 mg/g of coffee in 48 h. Parchment resistance reduced the transfer of these precursors by up to 60%. Fructose underwent germination-related metabolic reactions, reducing its amount in the beans and reaching 1.9 ± 0.62 mg/g in 48 h. During fermentation in real conditions, lactic acid and alanine were produced and transferred into the coffee beans after a 12 h latency phase. The LSCC2 strain produced significantly more lactic acid and alanine and consumed fructose more slowly than LSCC3.

Exploring Microbial Influence on Flavor Development during Coffee Processing in Humid Subtropical Climate through Metagenetic–Metabolomics Analysis

“…Regarding coffee quality, ethanol acts as a byproduct that contributes to esters and other aromatic compounds’ formation, essential for the coffee’s flavor complexity and depth. Lactic acid, in turn, provides a milder and more pleasant profile than other acids [ 8 , 9 ]. Conversely, the role of acetic acid in fermentation remains uncertain; however, concentrations above 1 g/L may detrimentally impact the final product’s quality [ 5 , 26 ].…”

“…Additionally, it generates ethanol, lactic acid, and various minor compounds, including esters, higher alcohols, aldehydes, and ketones. Coffee beverages derived from wet fermentation exhibit distinct sensory characteristics, such as higher acidity, a lighter body, and a more pronounced aroma compared to dry-processed coffees [ 8 , 9 ]. This disparity can be attributed to the varying metabolic activities of sugars and free amino acids within the seeds, along with intense microbial activity that enhances floral and fruity aromas [ 2 ].…”