# Brewing with Unmulated Cereal Adjuncts: Sensory and Analytical Impacts on Beer Quality
## 3 Results and Discussion
### Analytical Evaluation of Adjunct Worts and Beers Versus an All Malt Control
#### 3.2.4 Analysis of Flavour-Active Fermentation Volatiles
The majority of the higher alcohols identified significantly increased with 60% maize and rice inclusion, whilst the concentration of these higher alcohols significantly decreased with barley (A), barley (B) and wheat inclusion (Table 7). Higher alcohols are biosynthesized by yeast during fermentation by two pathways; the Ehrlich pathway for amino acid catabolism and by means of the anabolic pathway for amino acid synthesis [41]. Higher alcohol production is closely related to wort nitrogen composition. When nitrogen content is sufficient, amino acids are transformed into higher alcohols in reactions involving branched-chain amino acid aminotransferase (BCAT) and ethanol dehydrogenase [42]. However, when nitrogen sources are low this activates glucose metabolism and forms large amounts of pyruvate and consequently higher alcohols [42]. Therefore, the increase in higher alcohols in 60% adjunct beers made from torrefied rice or maize could be explained by the very low wort FAN concentrations (Table 4). Esters are one of the most important groups of flavour compounds produced by yeast as esters have a very low odour threshold and impart a range of fruity and floral aromas to the final product. However, if overproduced during fermentation, they can negatively affect the beer [40]. Ester production is affected by many fermentation parameters such as yeast strain, fermentation temperatures and changes in fermentation medium. An important parameter is the carbon-to-nitrogen ratio of the fermentation medium. The data in Table 7 indicate that all identified acetate and ethyl esters reduced in concentration with the addition of any unmalted adjuncts. Previous studies have determined that decreasing FAN concentration decreases the concentration of acetate esters and ethyl esters such as ethyl octanoate and decanoate [43]. Similar patterns were observed in this study, as ester concentrations decreased in the beers with corresponding decreases in FAN concentration. Improving the nitrogen composition and concentration could minimise significant variation in the volatile profile observed with adjunct use. Interestingly, the 60% unmalted wheat beer had the most similar volatile profile to the 100% malt control, with significantly different concentrations only observed for acetaldehyde, tryptophan, isobutanol and ethyl pentanoate. To explore the reasons for significant sensory differences in sweetcom/cooked vegetable aroma amongst trial beers (Table 2), their sulphur volatile profiles were determined using GC-PFPD (Table 8). A range of sulphur compounds (e.g., sulphides, thiols, thioesters) are known for adding cooked vegetable and sweetcom characters to beer. Sulphur volatiles have low flavour thresholds and can make a sensory impact at low concentrations. Sulphur compounds can originate from the raw materials, Maillard browning reaction and yeast metabolism during fermentation [44]. Dimethyl sulphide (DMS), which imparts a tinned sweetcom aroma to beer, was identified in all beers with the highest concentration obtained in the all-malt beer. The decrease in DMS is expected with the use of unmalted adjuncts and is due to their reduced contents of DMS precursor, S-methylmethionine (SMM). SMM is developed during germination of the grain and is then broken down to DMS during thermal processes such as kilining [45]. In the present data set, DMS concentrations did not directly correlate to