Abstract
The effects of different malolactic bacteria fermentation techniques on the bioconversion of aromatic compounds in cool-climate grape wines were examined. During three wine seasons, red and white grape wines were produced using various malolactic fermentation induction techniques: Coinoculation, sequential inoculation, and spontaneous process. Volatile compounds (diacetyl and the products of its metabolism, and selected ethyl fatty acid esters) were extracted by solid phase microextraction. Compounds were identified with a multidimensional gas chromatograph—GC × GC-ToFMS with ZOEX cryogenic (N2) modulator. Sensory evaluation of the wines was also performed. It was found that the fermentation-derived metabolites studied were affected by the malolactic bacteria inoculation regime. Quantitatively, ethyl lactate, diethyl succinate, and ethyl acetate dominated as esters with the largest increase in content. The total concentration of ethyl esters was highest for the coinoculation technique, while the highest concentration of diacetyl was noted for the spontaneous technique. Controlled malolactic fermentation, especially using the coinoculation technique, can be proposed as a safe and efficient enological practice for producing quality cool-climate grape wines enriched with fruity, fresh, and floral aromas.
Highlights
Malolactic fermentation (MLF) is a secondary fermentation that takes place after alcoholic fermentation in the process of grape wine production
Our research focused on selected aroma compounds synthesized during malolactic fermentation in white and red grape wines produced by three different methods of inoculation: (1) Coinoculation (COI), where the yeast and bacteria were inoculated at the same time; (2) sequential inoculation (SEQI), where malolactic fermentation was induced at the end of alcoholic fermentation; and (3) spontaneous malolactic fermentation (SPONT), where malolactic bacteria (MLB) inoculation was not performed
For the sequential inoculation variant in which MLF was induced at the end of alcoholic fermentation (AF), bacteria inoculation was applied after one week
Summary
Malolactic fermentation (MLF) is a secondary fermentation that takes place after alcoholic fermentation in the process of grape wine production. It is used in the majority of red wines, some white wines, and generally for wines with enhanced acidity. The MLB utilize malic acid, and the residual sugars left by yeast after the alcoholic fermentation. This reduces the potential carbon source for spoilage microbiota, and increases microbial stabilization of the wine [1,2,3,4,5]
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