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Starter cultures play an important role in aroma formation in cheese. However, certain strains may produce aroma compounds in higher concentrations leading to an undesired off-flavor such as malty or chocolate. According to our knowledge, this flavor is attributed to the presence of 2/3-methylbutanal in higher concentrations. The production of the compounds seems to depend on the thermal process during cheese production and the environment in which the strains develop. In this study we tried to quantify those compounds and identify possible other compounds. The qualitative and semi-quantitative analyzes of this study were carried out by headspace solid-phase microextraction gas chromatography – mass spectrometry (HS-SPME-GC-MS). In order to identify and characterize molecules responsible for malty/chocolate flavor in semi-hard cheese, analyses were conducted using in-tube extraction gas chromatography – mass spectrometry – olfactometry (ITEX-GC-MS-O) and two dimensional gas chromatography Heart-cut (GCxGC Heart-cut). We discovered that 2-methylbutanal, 3-methylbutanal, 2-methylbutanol and 3-methylbutanol were the main responsible compounds for the malty/chocolate flavor. However, other molecules such as phenylacetaldehyde and 2-phenylbutenal (also known as cocoa butenal) were also present in higher amounts in highly malted/chocolate flavored cheeses. Those have not been identified in this category of odors by the panelists during the olfactometric analyzes by ITEX-GC-MS-O and GCxGC heart-cut because the concentrations of these two compounds were most likely below their respective odor threshold. Nevertheless, a correlation between malty/chocolate flavor and those compounds could be made. Finally, kinetics of the target molecules were established by making bacterial cultures in milk. The validation of the results was made by making lab-scale cheeses which confirmed the results from the milk assays. A correlation between the flavor formation and pH/redox-potential could not be drawn.