## 3 Results and Discussion
### Main Volatile Compounds in the Different Experimental Beers
\begin{table}
\begin{tabular}{c c c c c c} \hline \multicolumn{6}{c}{**Main By-Products (mg/L)**} \\ \hline  & & **P4** & **P4-CR1** & **P4-LC2-1** & **P4-TSF** & **P4-CZ3** \\ \hline \multirow{8}{*}{**PW**} & \(n\)-Propanol & 8.47 \(\pm\) 0.37 \({}^{\text{a}}\) & 9.19 \(\pm\) 0.41 \({}^{\text{ac}}\) & 9.04 \(\pm\) 0.36 \({}^{\text{ac}}\) & 11.58 \(\pm\) 0.01 \({}^{\text{b}}\) & 9.80 \(\pm\) 0.14 \({}^{\text{c}}\) \\  & Isobutanol & 86.50 \(\pm\) 1.63 \({}^{\text{a}}\) & 98.19 \(\pm\) 4.06 \({}^{\text{ab}}\) & 110.65 \(\pm\) 12.22 \({}^{\text{bc}}\) & 127.16 \(\pm\) 3.31 \({}^{\text{c}}\) & 115.59 \(\pm\) 3.35 \({}^{\text{c}}\) \\  & \(n\)-Butanol & 132.61 \(\pm\) 5.04 \({}^{\text{a}}\) & 147.39 \(\pm\) 0.18 \({}^{\text{b}}\) & 160.75 \(\pm\) 5.60 \({}^{\text{bc}}\) & 157.97 \(\pm\) 0.14 \({}^{\text{bc}}\) & 173.43 \(\pm\) 4.80 \({}^{\text{c}}\) \\  & Active amyl alcohol & 21.13 \(\pm\) 2.69 \({}^{\text{a}}\) & 21.82 \(\pm\) 0.81 \({}^{\text{a}}\) & 21.87 \(\pm\) 0.61 \({}^{\text{a}}\) & 20.35 \(\pm\) 2.31 \({}^{\text{a}}\) & 33.09 \(\pm\) 1.14 \({}^{\text{b}}\) \\  & Isoamyl alcohol & 59.17 \(\pm\) 1.02 \({}^{\text{a}}\) & 57.82 \(\pm\) 3.42 \({}^{\text{ab}}\) & 70.07 \(\pm\) 0.37 \({}^{\text{ac}}\) & 61.90 \(\pm\) 4.61 \({}^{\text{a}}\) & 63.27 \(\pm\) 2.65 \({}^{\text{a}}\) \\  & Ethyl acetate & 9.45 \(\pm\) 0.52 \({}^{\text{a}}\) & 10.42 \(\pm\) 4.44 \({}^{\text{a}}\) & 15.42 \(\pm\) 1.72 \({}^{\text{b}}\) & 16.94 \(\pm\) 0.37 \({}^{\text{b}}\) & 7.55 \(\pm\) 0.35 \({}^{\text{a}}\) \\  & Acetaldehyde & 52.46 \(\pm\) 1.91 \({}^{\text{a}}\) & 57.00 \(\pm\) 2.12 \({}^{\text{a}}\) & 58.81 \(\pm\) 0.39 \({}^{\text{a}}\) & 45.74 \(\pm\) 3.46 \({}^{\text{ab}}\) & 38.2 \(\pm\) 5.44 \({}^{\text{b}}\) \\  & Acetoin & 12.86 \(\pm\) 2.42 \({}^{\text{a}}\) & 12.82 \(\pm\) 1.46 \({}^{\text{a}}\) & 15.11 \(\pm\) 2.28 \({}^{\text{a}}\) & 14.95 \(\pm\) 1.41 \({}^{\text{a}}\) & 26.31 \(\pm\) 0.10 \({}^{\text{b}}\) \\ \hline \multirow{8}{*}{**WW**} & \(n\)-Propanol & 14.43 \(\pm\) 0.47 \({}^{\text{a}}\) & 12.32 \(\pm\) 0.67 \({}^{\text{b}}\) & 8.54 \(\pm\) 0.11 \({}^{\text{c}}\) & 10.08 \(\pm\) 0.16 \({}^{\text{c}}\) & 9.80 \(\pm\) 0.55 \({}^{\text{c}}\) \\  & Isobutanol & 53.68 \(\pm\) 2.55 \({}^{\text{a}}\) & 69.73 \(\pm\) 2.94 \({}^{\text{b}}\) & 78.51 \(\pm\) 3.83 \({}^{\text{b}}\) & 76.63 \(\pm\) 1.56 \({}^{\text{b}}\) & 115.79 \(\pm\) 3.14 \({}^{\text{c}}\) \\  & \(n\)-Butanol & 65.87 \(\pm\) 3.44 \({}^{\text{a}}\) & 112.44 \(\pm\) 2.19 \({}^{\text{b}}\) & 123.21 \(\pm\) 4.91 \({}^{\text{b}}\) & 115.55 \(\pm\) 5.29 \({}^{\text{b}}\) & 173.42 \(\pm\) 4.64 \({}^{\text{c}}\) \\  & Active amyl alcohol & 20.50 \(\pm\) 1.07 \({}^{\text{a}}\) & 22.95 \(\pm\) 1.09 \({}^{\text{ab}}\) & 20.03 \(\pm\) 1.14 \({}^{\text{a}}\) & 20.04 \(\pm\) 0.38 \({}^{\text{a}}\) & 28.10 \(\pm\) 3.30 \({}^{\text{b}}\) \\  & Isoamyl alcohol & 58.25 \(\pm\) 2.13 & 62.05 \(\pm\) 2.48 & 62.87 \(\pm\) 2.66 & 56.54 \(\pm\) 1.26 & 63.33 \(\pm\) 3.86 \\  & Ethyl acetate & 6.28 \(\pm\) 0.08 & 7.87 \(\pm\) 0.18 & 7.67 \(\pm\) 0.27 & 7.90 \(\pm\) 0.18 & 7.69 \(\pm\) 0.082 \\  & Acetaldehyde & 49.41 \(\pm\) 6.91 \({}^{\text{a}}\) & 60.23 \(\pm\) 4.20 \({}^{\text{ab}}\) & 52.35 \(\pm\) 5.50 \({}^{\text{a}}\) & 52.97 \(\pm\) 3.65 \({}^{\text{a}}\) & 38.29 \(\pm\) 2.29 \({}^{\text{ac}}\) \\  & Acetoin & 13.22 \(\pm\) 2.07 \({}^{\text{a}}\) & 13.75 \(\pm\) 1.17 \({}^{\text{a}}\) & 14.01 \(\pm\) 0.06 \({}^{\text{a}}\) & 14.28 \(\pm\) 1.10 \({}^{\text{a}}\) & 33.83 \(\pm\) 2.79 \({}^{\text{b}}\) \\ \hline \multirow{8}{*}{**AW**} & \(n\)-Propanol & 13.68 \(\pm\) 1.14 \({}^{\text{a}}\) & 13.51 \(\pm\) 0.79 \({}^{\text{a}}\) & 9.71 \(\pm\) 0.36 \({}^{\text{ab}}\) & 15.01 \(\pm\) 1.91 \({}^{\text{ac}}\) & 17.34 The analysis of the data relating to the secondary compounds showed a non-univocal behaviour of the starter cultures in the three tested beers, even if some results were confirmed in all the fermentations, such as the low production of isobutanol, \(n\)-butanol and acetoin by the single starter P4.