## 3 Results and Discussion
### Analytical Parameters of the Experimental Beers  
At the end of the fermentation process, the experimental beers produced by single and mixed starters in the three different words (PW, WW and AW) were analysed for analytical parameters and by-products related to organoleptic quality. The results regarding the main analytical parameters are reported in Table 2. The data of each beer produced by mixed cultures were compared by one-way ANOVA with the data from the beer obtained from the single starter P4 in the corresponding word. No significant differences were detected for the final real extract (FRE), expressed as Plato degree, which ranged between 3.0 and 4.0 in Pilsner wort. The lowest value was recorded by P4 beer in WW (2.5) and the same value (4.0) was found in all the beers produced in AW (data not shown). As regards the apparent and real attenuation (AA and RA), high values were found in beers produced both by the mixed cultures and the pure culture (P4) in PW and WW, whereas the Amber beers exhibited the lowest values for both parameters. Statistical differences were found in all the beers for volatile acidity (calculated as acetic acid) and \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & **P4** & **P4-CR1** & **P4-LC2-1** & **P4-TSF** & **P4-CZ3** \\ \hline \multirow{4}{*}{**PW**} & AA & 81.24 \(\pm\) 6.78 & 81.30 \(\pm\) 6.70 & 67.70 \(\pm\) 5.8 & 81.54 \(\pm\) 4.31 & 81.52 \(\pm\) 4.8 \\  & RA & 66.65 \(\pm\) 3.90 & 66.70 \(\pm\) 4.33 & 55.52 \(\pm\) 3.98 & 66.90 \(\pm\) 3.54 & 66.88 \(\pm\) 3.55 \\  & VA & 0.13 \(\pm\) 0.01 a & 0.23 \(\pm\) 0.009 b & 0.30 \(\pm\) 0.013 c & 0.31 \(\pm\) 0.015 c & 0.41 \(\pm\) 0.007 d \\  & AC & 3.09 \(\pm\) 0.02 a & 3.03 \(\pm\) 0.05 abc & 2.89 \(\pm\) 0.01 b & 2.87 \(\pm\) 0.06 b & 2.80 \(\pm\) 0.03 b \\ \hline \multirow{4}{*}{**WW**} & AA & 88.10 \(\pm\) 4.8 & 74.60 \(\pm\) 4.78 & 81.22 \(\pm\) 4.75 & 81.54 \(\pm\) 4.31 & 81.30 \(\pm\) 4.88 \\  & RA & 72.20 \(\pm\) 3.96 & 61.10 \(\pm\) 3.92 & 66.64 \(\pm\) 3.90 & 66.90 \(\pm\) 3.54 & 66.69 \(\pm\) 3.55 \\  & VA & 0.24 \(\pm\) 0.013 a & 0.35 \(\pm\) 0.012 b & 0.39 \(\pm\) 0.01 b & 0.35 \(\pm\) 0.006 b & 0.60 \(\pm\) 0.008 c \\  & AC & 3.10 \(\pm\) 0.02 a & 3.02 \(\pm\) 0.06 a & 2.86 \(\pm\) 0.02 b & 2.92 \(\pm\) 0.01 ab & 2.63 \(\pm\) 0.05 c \\ \hline \multirow{4}{*}{**AW**} & AA & 70.60 \(\pm\) 6.4 & 70.58 \(\pm\) 0.08 & 70.27 \(\pm\) 0.11 & 70.38 \(\pm\) 0.31 & 70.38 \(\pm\) 0.13 \\  & RA & 57.90 \(\pm\) 3.73 & 57.88 \(\pm\) 0.02 & 57.63 \(\pm\) 0.37 & 57.72 \(\pm\) 0.74 & 57.68 \(\pm\) 0.32 \\ \cline{1-1}  & VA & 0.51 \(\pm\) 0.018 a & 0.44 \(\pm\) 0.016 b & 0.56 \(\pm\) 0.004 a & 0.55 \(\pm\) 0.015 a & 0.41 \(\pm\) 0.020 c \\ \cline{1-1}  & AC & 3.19 \(\pm\) 0.04 & 3.25 \(\pm\) 0.03 & 3.13 \(\pm\) 0.07 & 3.12 \(\pm\) 0.08 & 3.08 \(\pm\) 0.02 \\ \hline \hline \end{tabular}  
* AA = apparent attenuation (%); RA = real attenuation (%); VA = volatile acidity (g/L); AC = alcohol content (% y/v).  
\end{table} 
Table 2: Main analytical characteristics of the experimental beers produced by pure (P4) and mixed cultures (P4-CR1, P4-LC2-1, P4-TSF, P4-CZ3) in the three different words (PW, WW and AW). For each parameter and each word, data with different superscript letters mean significant differences (Tukey’s test; \(p\leq\) 0.05) between beers produced by the single and mixed starters. for alcohol content (AC) in all the samples, except for those produced in AW. In beers obtained from PW and WW, the single starter fermentations produced beers containing a significantly lower level of volatile acidity than samples from mixed starters, whereas in AW beers, the lowest level of volatile acidity was detected in beer fermented with the mixed starter containing the _Z. bailii_ strain (P4-CR1). Our results are in contrast to the traditional features assigned to _Z. bailii_ species, as this yeast is frequently associated with wine spoilage in consequence of high production of volatile acidity [42; 43], confirming the key role of biodiversity at strain level.