## 3 Results and Discussion
### Filtration Impact on NABs Breved and Analyzed
#### 3.3.2 Filtration and Its Impact on Selected Volatile Compounds in Fresh NABs  
The current volatile compound analysis is limited to a narrow range of substances, primarily focusing on aldehydes and ethyl esters. While these compounds are important markers of flavor [51], this restricted scope overlooks other critical flavor-active compounds that significantly influence beer quality. For instance, diacetyl--a basic flavor compound \begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & **Filter Inlet** & **Filter Outlet** & **Filter Outlet** & **Filter Outlet** & **Filter Outlet** \\  & & **AF 11** & **AF 31** & **AF 71** & **AF 101** \\ \hline
**Color [EBC]** & & & & & \\ LA-01 & 5.5 b \(\pm\) 0.0 & \(\mathrm{Haze}\) b,* & 4.7 a \(\pm\) 0.0 & 4.7 a \(\pm\) 0.1 & 4.6 a \(\pm\) 0.0 \\ LoNa & 5.4 c \(\pm\) 0.0 & \(\mathrm{Haze}\) b,* & 4.7 a \(\pm\) 0.0 & 4.4 b \(\pm\) 0.0 & 4.7 a \(\pm\) 0.0 \\ W-34/70 & 7.1 a \(\pm\) 0.0 & 4.4 a \(\pm\) 0.0 & 4.2 b \(\pm\) 0.0 & 4.1 c \(\pm\) 0.0 & 4.2 b \(\pm\) 0.0 \\ \hline
**Bitterness [BU]** & & & & & \\ LA-01 & 11.1 a \(\pm\) 0.2 & 11.3 a \(\pm\) 0.0 & 11.3 a \(\pm\) 0.0 & 11.4 a \(\pm\) 0.1 & 11.4 a \(\pm\) 0.0 \\ LoNa & 11.0 a \(\pm\) 0.0 & 11.4 a \(\pm\) 0.1 & 11.0 ab \(\pm\) 0.0 & 11.1 b \(\pm\) 0.1 & 11.0 b \(\pm\) 0.0 \\ W-34/70 & 11.2 a \(\pm\) 0.1 & 9.6 b \(\pm\) 0.1 & 10.3 b \(\pm\) 0.3 & 9.5 c \(\pm\) 0.1 & 9.7 c \(\pm\) 0.0 \\ \hline \hline \end{tabular}  
* Haze—due to the elevated turbidity observed after filtration with AF 11 for LA-01 and LoNa, color measurements could not be conducted.  
\end{table} 
Table 2: Color and bitterness results for NABs produced with the three different yeast strains and filtered using various filter sheet setups; superscript letters indicate LS mean groupings (Fisher LSD, \(p\) < 0.05). known for its buttery aroma [11; 51]--plays a crucial role in sensory perception and will be included in further investigations to provide a more comprehensive flavor profile. Volatile compounds in full-strength beer encompass various groups of flavor-related chemicals [5; 26; 52; 53]. Modifications in production processes, such as dry hopping, metabolic regulation, or thermal treatments for non-alcoholic beer production, can further alter these compounds in fresh beer prior to filtration [4; 5; 10]. Since the aroma and flavor of non-alcoholic beers influence consumer perception and repurchase decisions, chemical volatile analysis serves as a valuable tool for product comparison. Selected aldehydes, hop aroma compounds, and esters were monitored before and after filtration (Figures 3-5). Figure 3: These graphs show aldehyde changes in the NABs tested with different filter setups. Letters indicate LS mean groupings (Fisher LSD, \(p\) < 0.05), and error bars show standard error. Figure 4: These graphs show hop aroma compound changes in the NABs tested with different filter setups. Letters indicate LS mean groupings (Fisher LSD, \(p\) < 0.05), and error bars show standard error. Aldehydes contribute to off-flavors that typically develop during aging, with specific compounds imparting distinct undesirable notes [5; 22; 52]. While aldehydes mainly originate from malt [54], modifications in production processes can alter their profile, potentially enhancing the fresh aroma impression while also improving the long-term stability of non-alcoholic beers [9; 52]. A statistically significant reduction in 2-methylpropanal (2 MP) and hexanal (C6 aldehyde) was observed (Figure 3). 2 MP was included in the analysis due to its known contribution to grainy, varnish-like, and fruity notes, with a reported flavor threshold of 86 ug/L [55], whereas hexanal imparts bitter, vinous, and aldehyde sensory impressions, with a higher threshold of 88-350 ug/L [55; 51].