## 2 Results and Discussion
### Ethyl Fatty Acid Esters  
The synthesis and hydrolysis of esters during the malolactic fermentation of wines has been described by many research groups, but there is a disagreement concerning the influence of this secondary fermentation action on the final concentration of esters. Most authors indicate that there is a significant enhancement in the ester content of wines that have undergone MLF [8; 10; 11; 12; 14; 15; 16; 17; 18; 19], but other researchers have presented a decreasing trend [20; 21; 22]. Malolactic bacteria strain selection has also been described as an important factor that determines the final concentrations of esters [12; 14; 16; 17]. Ethyl fatty acid esters are compounds considered to be of primary importance for the aroma of wines. The compounds analyzed include ethyl lactate, diethyl succinate, ethyl propanoate, ethyl hexanoate, ethyl octanoate, and acetate esters (ethyl acetate, isoamyl acetate, and 2-phenethyl acetate). Ethyl lactate, one of the most characteristic aromatic compounds produced during malolactic fermentation, is synthetized in the course of the esterification of ethanol (produced by yeast during alcoholic fermentation) and lactate (produced by malolactic bacteria during malolactic fermentation). When the malolactic process takes place, the concentration of ethyl lactate progressively increases. This is beneficial to the wine bouquet due to its fruity, buttery, and creamy aromas, and it also contributes to the sensations of roundness in the mouth [16; 23]. Some authors suggest that the insensitivity of ethyl lactate biosynthesis depends on the strain of _O. oeni_ used [9; 15; 17; 24]. On the other hand, some other authors did not register any dependence of ethyl lactate biosynthesis on the bacteria strain [12]. In our study, the concentration of ethyl lactate after alcoholic fermentation falls in the 8.54-14.44 g/L range (Table 2), and this significantly increased as a result of malolactic fermentation. The highest concentration of ethyl lactate was registered in the coinoculation technique (132.57-173.76 mg/L). After sequential inoculation of MLB and spontaneous MLF, the concentrations of ethyl lactate were significantly lower (41.64-115.63 mg/L). However, this value was several times higher than without MLF (Table 2). The ethyl lactate biosynthesis was thus noted as strongly influenced by the method of malolactic fermentation induction. For the coinoculation variant (with the highest dynamics and effectiveness of malolactic bioconversion) [13], the highest ethyl lactate concentration in the final wine was obtained (Table 2). Whereas, in the variants with lower MLF rate, a lower ethyl lactate synthesis was noted. Literature studies have reported a wide range of ethyl lactate concentrations in wines that have undergone MLF. Values significantly higher than ours were described by [PERSON] et al. (up to 440 mg/L) [17], [PERSON] et al. (up to 235 mg/L) [15], and [PERSON] and [PERSON] (up to 190 mg/L) [25]. Our results are similar to those of [PERSON] et al., who found ethyl lactate in wines after MLF at concentrations ranging from 90 to 150 mg/L [26]. On the other hand, [PERSON] [27] and [PERSON] et al. [14] described standard concentrations for ethyl lactate in red wines of up to 50 mg/L. The aroma threshold for ethyl lactate has been determined to be 110 mg/L [26]. In line with this, ethyl lactate was discernible in our experiment only in wines in which the yeast and MLB had been coinoculated. Diethyl succinate is another volatile compound that contributes to wine aroma. Succinic acid (a by-product of microbial \(\alpha\)-ketoglutate metabolism) is esterified to diethyl succinate, which brings-fruity melon notes. This compound occurs naturally in apples, grapes, and cocoa. Its odor threshold has been set at 1.2 mg/L [28]. When only alcoholic fermentation was performed in our experiments, the concentration of this compound was found to be under the threshold value (up to 0.68 mg/L).