## 2 Results and Discussion
### Diacetyl and Its Metabolic Products
The highest concentrations were noted for the spontaneous process, in which the biosynthesis yield was as high as 8.79-12.52 mg/L of acetoin, and 652-806 mg/L of 2,3-butanediol. Coinoculation resulted in significantly lower values of both metabolites than sequential inoculation. According to [PERSON] and [PERSON] [PERSON] and [PERSON] (1973), and [PERSON] and [PERSON] (1999), acetoin levels remained under the sensory threshold, but 2,3-butanediol reached a concentration of sensory significance for wine (over 600 mg/dm\({}^{3}\)), though only in the spontaneous variants. This was reflected in the sensory evaluation of the produced wines (Figure 1). Generally, 2,3-butanediol is not expected to affect the sensory qualities of wine appreciably [PERSON] and [PERSON] (1973), but we did note a bitter taste in these variants. Some authors have also described very low or undetectable levels of diacetyl in wines that had undergone MLF [PERSON] and [PERSON] (1973). They suggest that this may be a result of the enzymatic reduction of diacetyl to 2,3-butanediol. Acetoin, the other intermediate metabolite of diacetyl involved in the same metabolic pathway, is also reduced to 2,3-butanediol. This may explain the high levels of 2,3-butanediol found in our wines. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **2,3-Butanedione** & **3-Hydroxy-2-Butanone** & **2,3-Butanediol** \\  & **(Diacetyl)** & **(Acetoin)** & **2,3-Butanediol** \\ \hline \hline \multirow{7}{*}{White wines} & Chardonnay & & \\   AF & 1.13 \(\pm\) 0.22 d & 0.86 \(\pm\) 0.06 d & 254.32 \(\pm\) 11.34 d \\   COI & 2.19 \(\pm\) 0.15 c & 3.11 \(\pm\) 0.39 c & 331.56 \(\pm\) 15.33 c \\   SEQI & 3.42 \(\pm\) 0.19 b & 5.95 \(\pm\) 0.26 b & 479.93 \(\pm\) 9.14 b \\   SPONT & 7.44 \(\pm\) 0.08 a & 8.79 \(\pm\) 0.42 a & 712.42 \(\pm\) 23.65 a \\   Kerhing & & & \\   AF & 0.94 \(\pm\) 0.24 d & 0.73 \(\pm\) 0.04 d & 165.36 \(\pm\) 12.75 d \\   COI & 3.02 \(\pm\) 0.16 c & 4.31 \(\pm\) 0.22 c & 349.62 \(\pm\) 16.83 c \\   SEQI & 4.09 \(\pm\) 0.08 b & 6.18 \(\pm\) 0.42 b & 513.88 \(\pm\) 8.31 b \\   SPONT & 8.33 \(\pm\) 0.22 a & 11.05 \(\pm\) 0.98 a & 783.63 \(\pm\) 10.63 a \\   Pinot nor A & & & \\   AF & 1.71 \(\pm\) 0.15 d & 1.62 \(\pm\) 0.17 d & 288.97 \(\pm\) 12.06 d \\   COI & 3.80 \(\pm\) 0.19 c & 5.11 \(\pm\) 0.36 c & 361.35 \(\pm\) 9.72 c \\   SEQI & 5.24 \(\pm\) 0.16 b & 6.94 \(\pm\) 0.45 b & 647.55 \(\pm\) 17.83 b \\   SPONT & 9.22 \(\pm\) 0.23 a & 12.39 \(\pm\) 0.41 a & 806.37 \(\pm\) 14.97 a \\   Pinot nor B & & & \\   AF & 1.31 \(\pm\) 0.14 d & 1.04 \(\pm\) 0.12 c & 267.42 \(\pm\) 8.53 d \\   Red wines & COI & 4.06 \(\pm\) 0.09 c & 6.48 \(\pm\) 0.48 b & 493.52 \(\pm\) 11.84 c \\   SEQI & 5.91 \(\pm\) 0.11 b & 7.17 \(\pm\) 0.56 b & 631.67 \(\pm\) 17.59 b \\   SPONT & 8.72 \(\pm\) 0.15 a & 12.52 \(\pm\) 0.46 a & 718.13 \(\pm\) 13.77 a \\   Rondo & & & \\   AF & 1.72 \(\pm\) 0.05 d & 1.53 \(\pm\) 0.14 d & 264.94 \(\pm\) 6.48 d \\   COI & 3.81 \(\pm\) 0.09 c & 4.97 \(\pm\) 0.32 c & 355.13 \(\pm\) 15.83 c \\   SEQI & 5.50 \(\pm\) 0.13 b & 7.03 \(\pm\) 0.26 b & 584.42 \(\pm\) 18.28 b \\   SPONT & 8.80 \(\pm\) 0.07 a & 11.43 \(\pm\) 0.31 a & 652.36 \(\pm\) 15.75 a \\ \hline \hline \multicolumn{4}{l}{The data are the mean of triplicates \(\pm\) SD; AF—only alcoholic fermentation; COI—coinoculation of yeast and bacteria; SEQI—sequential inoculation: bacteria at the end of AF; SPONT—spontaneous MLF; a, b, c, d—denotes statistically significant differences (\(p<0.05\)) between the different inoculation techniques.} \\ \end{tabular}
\end{table} 
Table 4: Concentrations (mg/L) of diacetyl, acetoin, and 2,3-butanediol in white and red grape wines produced by different methods of MLF induction; parameters were evaluated three months after bottling. Figure 1: Descriptive sensory evaluation of white and red wines produced by different methods of MLF induction; evaluation was performed three months after bottling.