## 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
In this study, filtration had no statistically significant effect on linalool concentrations (Figure 4), suggesting that the impact of filtration on linalool-driven sensory impressions is negligible. Given the importance of linalool in defining hop character, this finding underscores the ability to preserve hop aroma during beer clarification processes. \(\upbeta\)-Citronellol, a compound associated with yeast metabolism [58; 61], showed elevated concentrations in the W-34/70 sample, likely due to the strain's higher fermentation activity. While \(\upbeta\)-citronellol levels tended to decrease slightly upon filtration, they remained above its reported flavor threshold of \(<\)10 \(\upmu\)g/L [58; 62]. From a purely chemical perspective, this suggests that the compound's lemon- or lime-like aroma [62] would still contribute to the sensory profile of the final product, even after filtration. Similar conclusions apply to geraniol. Although the observed variation in geraniol concentrations was slightly greater, no filtration-induced reductions were statistically observed. This is particularly relevant, as the flavor threshold for geraniol is also \(<\)10 ug/L [58], and this value was not undercut in any of the filtered samples. Therefore, from a chemical standpoint, filtration does not appear to compromise the geraniol-derived sensory attributes of the NABs. \(\alpha\)-Terpineol (associated with lilac-like aroma [62]; threshold 2000 ug/L [51]), \(\alpha\)-humulene (spicy, woody character; threshold 120-450 ug/L [63]), and \(\beta\)-caryophyllene (also described as spicy and woody; threshold 230 ug/L [63]) were all detected at concentrations well below their respective flavor thresholds. Moreover, their levels remained unaffected by filtration. From a chemical standpoint, this indicates that their already minimal contribution to the overall sensory profile of the NABs is not altered by the filtration process. As previously mentioned, esters represent another crucial group of aroma compounds in beer [52]. Their significance lies in their synergistic interactions, where a combination of esters and other volatile compounds can activate flavors below their individual perception thresholds. Given their inherently low flavor thresholds [51], even slight changes in ester concentrations can alter the overall aroma and flavor profile of beer [53; 59]. To assess potential filtration effects, ethyl hexanoate (apple, fruity, sweetish flavor impressions; threshold 230 ug/L [51]) and ethyl octanoate (apple, fruity, sweetish flavor impressions; threshold 900 ug/L [51]) were selected as representative fermentation-derived esters (Figure 5). The results indicate that the filtration of LA-01 and LoNa with AF 11 led to statistically significant differences compared to treatments using AF 31, AF 71, and AF 101. While ester concentrations decreased when LA-01 and LoNa were filtered with AF 11, a much more pronounced reduction was observed in the other filtration treatments. In contrast, W-34/70 exhibited relatively consistent ester concentrations across all filtration treatments, mirroring the comparable turbidity readings obtained in these trials (Figure 2). When considering the sensory thresholds of the esters analyzed [51], the reductions observed due to filtration must be interpreted with caution. Although the absolute concentrations of esters such as ethyl hexanoate and ethyl octanoate remained below or near their individual flavor thresholds, their decline may still represent a critical sensory change--from a chemical standpoint. This is because esters are known to act synergistically with other volatile compounds, meaning that their combined presence can enhance fruity and floral flavor impressions even when individual concentrations are below perceptual limits [52]. Therefore, any reduction in ester levels may lead to a perceptible decrease in the overall aroma complexity and fruity character of the beer. In this context, ester retention becomes even more critical for achieving a well-rounded and appealing sensory profile [5; 26].