## 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
Although the initial concentrations and the observed reductions in the NABs produced remained below these thresholds, making a noticeable impact on fresh flavor unlikely, previous studies have demonstrated that 2 MP and hexanal levels can increase during storage, contributing to oxidative off-flavors in lager-style beers over time [56]. The reduction in these aldehyde observations is likely linked to yeast reduction, as it is anticipated that yeast can bind aldehydes [57]. For LA-01 and LoNa, the aldehyde concentrations decreased after filtration  
Figure 5: These graphs show ester 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. with AF 11 compared to the filter inlet yet remained higher than those observed for AF 31, AF 71, and AF 101. This finding is noteworthy, as it highlights a beneficial effect in reducing aldehydes, which can contribute to off-flavors in specific beer styles over time [22; 55; 56]. In contrast, the filtration of W-34/70 led to the highest turbidity reduction across all filter sheets (Figure 2) but no statistically significant differences in 2 MP and hexanal levels among filtered samples (Figure 3). Since no sensory evaluation was conducted in this study, only chemical correlations between certain compounds and their concentration-dependent off-flavors can be inferred. Notably, nonanal (C9 aldehyde) remained mainly unaffected by filtration (Figure 3), suggesting that its increased chain length prevents binding to yeast in the same manner as hexanal (C6 aldehyde). Consequently, reducing yeast content in NABs does not lead to the efficient extraction of nonanal. A similar pattern was observed for furfural (Figure 3), an aldehyde associated with off-flavors (paper, caramel, bready, sensory impressions [51; 55]) in beer and known to increase with temperature during storage [52; 55]. Due to furfural's aldehyde group attachment at the second position of the furan ring, yeast binding is unlikely, explaining the statistically insignificant changes observed across all yeast strains and filter sheets tested. In contrast to aldehydes, which are predominantly associated with off-flavors [55], both brewers and consumers seek specific volatile compounds that contribute desirable aromas to beer, including non-alcoholic beers [52]. These compounds primarily include hop-derived volatiles (Figure 4) [58] and fermentation-related esters (Figure 5) [52], both of which play a crucial role in defining the sensory characteristics of the final product [26]. Filtration had little to no statistical impact on hop aroma compounds in the NABs tested (Figure 4). The minor but statistically significant changes observed can likely be attributed to factors such as sampling variability, sample preparation inconsistencies, and the inherent measurement uncertainty of the analytical method. These factors were not accounted for in the ANOVA performed in this study, suggesting that the observed variations may not necessarily indicate a true filtration effect. Given the importance of hop-derived volatiles in beer aroma [53; 58; 59], the minimal impact of filtration on these compounds is a valuable finding. It suggests that filtration does not significantly alter the hop profile of lager-style NABs. The hop-derived compounds analyzed in this study represent some of the most common and sensorially relevant volatiles found in beer [58]. Myrcene, for example, is a major contributor to fresh hop aroma, typically present in concentrations ranging from 30 to 100 \(\upmu\)g/L, and is described as having resinous, pine-like, and herbal characteristics [58]. Although the concentrations detected in this study were below the typical flavor threshold, they remained unaffected by filtration. Linalool, a key compound of hop oil [60], also contributes to hoppy beer aroma, with a reported flavor threshold below 10 \(\upmu\)g/L (R-linalool, beer-specific) [58].