## 3 Results and Discussion
### Interpretation of Analysis in Various Fermentation Conditions
When producing non-alcoholic beers by stopping fermentation, the main objective is to reduce the impression of bad taste or to limit it from the beginning and for diacetyl concentrations between 11 and 12 \(\mu\)g/L (Figure 2). Fermentation coupled with the thermal process represents the easiest method to have an alcohol-free beer, the application of heating between 35 \({}^{\circ}\)C and 60 \({}^{\circ}\)C until boiling results in the elimination of alcohol and other volatile substances such as esters and higher alcohols consequently increasing the turbidity of the 0.3 to 2.5 IBC (Table 5) [34]. The final beer product under different conditions was analyzed by GC to identify its aroma compounds. The results show that the concentration of diacetyl also increases between the stop of fermentation and the release of the final product, with the concentration of diacetyl at the last day of fermentation is equal to 12 \(\mu\)g/L this concentration increases up to 160 \(\mu\)g/L in the final product. This difference requires control of factors such as oxygen level and temperature between the fermentation stage and the release of the final product (Table 6, Figure 3). Figure 1: Monitoring of diacetyl concentration during classical fermentation. At the end of fermentation, oxygen is eliminated from the milieu because it is consumed during the respiration phase of the yeast. The remaining quantity is used during fermentation because it is essential in the biosynthesis of sterols, which are essential molecules for the maintenance of cell walls and give the yeast a high rate of viability. After filtration process, the oxygen concentration is higher than measured in the holding tank (after the end of fermentation). This concentration decreases over time. This occurs due to removing the air bubbles formed at the beginning of the filtration process. \begin{table}
\begin{tabular}{l c c c} \hline \hline \multirow{2}{*}{**Detected Compounds**} & **Final Product of Beer by** & **Final Product of Non-Alcoholic** & **Final Product of** \\  & **Using Classical** & **Beer by Using Stopping** & **Non-Alcoholic Beer by** \\  & **Fermentation** & **Fermentation** & **Using Thermal Process** \\ \hline Ethanol (vol\(\%\)) & 5.2 & 0.4 & 0.02 \\ Acetaldehyde (mg/L) & 7.2 & 8.5 & 4.0 \\ Propanol (mg/L) & 22 & 9 & Not detected \\ Ethyl acetate (mg/L) & 20.2 & 3.4 & Not detected \\ Isobutanol (mg/L) & 21.4 & 3.2 & Not detected \\ Isoamyl acetate (mg/L) & 2.35 & 0.12 & Not detected \\
3-methylbutanol (mg/L) & 60.1 & 1.25 & 0.25 \\
2-methylbutanol (mg/L) & 20.2 & Traces & Traces \\ Phenylethanol (mg/L) & 33.11 & 35.1 & 38.5 \\ Furfuryl alcohol (mg/L) & 3.11 & 2.6 & 2.411 \\ Diacetyl (mg/L) & 0.16 & 0.36 & 0.07 \\ DMS (\(\mu\)g/L) & 22 & 45 & Not detected \\ Turbidity (IBC) & 0.35 & 1.5 & 2.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Aromatic compounds and turbidity of the final product of alcoholic and de-alcoholized beer in various fermentation conditions determined by GC. Figure 2: Monitoring of diacetyl concentration during stopping fermentation. The water used in the preparation of the filtration layers contains a significant amount of oxygen. At the filler inlet, the oxygen concentration decreases proportionally with increasing temperature, this is due to the fact that oxygen is less soluble at higher temperatures. ([PERSON]'s law), (Figure 4). In general, the dissolution of oxygen in beer is high if the temperature is low and the pressure is high. The length of the pipes increases the risk of oxygen saturation in the beer. Aeration at the beginning of fermentation with less than 10 g/L is not a potential risk of oxidation since the yeast consumes the remaining oxygen during secondary fermentation. Controlling the pressure stability of clear beer tanks should be carried out to optimize the rate of oxygen removal by carbon dioxide.