# 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 key flavour-active compounds in beer are yeast secondary metabolites produced during fermentation and are composed of aldehydes, esters, higher alcohols and sulphur compounds. The trial beers were analysed using gas chromatography to identify and quantify these flavour active compounds (Table 7). The acetaldehyde concentration was considerably higher in 60% rice beer compared to the sample set. This finding is in agreement with the work of [PERSON] et al. [16] who reported that beer produced with an all rice grist had acetaldehyde concentrations three times over the flavour threshold (10 mg/L). Acetaldehyde is known for imparting a green apple/emulsion paint character as reflected in the attribute description used in the sensory lexicon (Table 1). Therefore, the significant increase of green apple flavour identified in the 60% rice sample is likely due to the elevated acetaldehyde concentrations. Acetaldehyde is produced as a result of decarboxylation of pyruvate and is an intermediate in the formation of ethanol during glycolysis [38]. Acetaldehyde concentration can be increased with word gravity, oxygen concentration, fermentation temperatures and yeast stress [38]. Since most of these conditions were standardised across the trial beers, this could have been related to yeast stress or sluggish fermentation as a result of the low FAN level in the 60% torrefied rice brew (Table 4). However, since other adjunct brews, e.g., 60% maize adjunct, were equally FAN constrained but did not result in such high acetaldehyde levels, there were clearly other yeast nutrition factors involved. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & & **(mg/L)** & & & \\ \cline{2-7}
**Beer Sample** & **4-HPA** & **Syring Acid** & **Vanillic Acid** & **4-HBA** & **Ferulic Acid** & **p-Coumaric Acid** & **Catechin** \\ \hline
100\% Malt & 2.30 & 0.52 & 1.41 & 0.59 & 3.52 & 2.79 & 2.60 \\
30\% Barley (A) & 1.58 ** & 0.32 ** & 1.56 & 0.52 & 2.55 ** & 1.60 ** & 2.01 \\
60\% Barley (A) & 2.21 & 0.42 & 2.07 ** & 0.70 & 3.05 & 2.22 ** & 2.92 \\
30\% Barley (B) & 1.33 ** & 0.21 ** & 1.11 & 0.47 & 1.83 ** & 1.75 ** & 3.71 ** \\
60\% Barley (B) & 1.32 ** & 0.16 ** & 1.53 & 0.48 & 2.67 ** & 1.62 ** & 3.43 ** \\
30\% Wheat & 1.62 ** & 0.40 & 1.48 & 0.63 & 2.73 ** & 1.37 ** & 0.97 ** \\
60\% Wheat & 1.56 ** & 0.56 & 1.84 ** & 0.52 & 3.49 & 1.11 ** & 0.80 ** \\
30\% Maize & 1.66 ** & 0.31 ** & 1.06 & 0.45 ** & 1.76 ** & 2.50 & 0.87 ** \\
60\% Maize & 1.00 ** & 0.23 ** & 0.35 ** & 0.52 & 1.94 ** & 3.11 & 0.75 ** \\
30\% Rice & 1.16 ** & 0.28 ** & 0.97 ** & 0.49 & 2.46 ** & 1.85 ** & 1.25 ** \\
60\% Rice & 2.39 & 0.32 ** & 0.70 ** & 0.85 ** & 2.11 ** & 1.57 ** & 0.94 ** \\ \hline ANOVA with [PERSON]’s post hoc analysis was used to compare the phenolic acid concentrations. Asterisks indicate samples that were significantly different compared to the all malt control (* \(p<\)0.05, ** \(p<\) 0.01). Data are the mean of four replicate measurements. 4-HBA = 4-hydroxybenzoic acid; 4-HPA = 4-hydroxyphenylacetic acid & \\ \hline \hline \end{tabular} ANOVA with [PERSON]’s post hoc analysis was used to compare the phenolic acid concentrations. Asterisks indicate samples that were significantly different compared to the all malt control (* \(p<\)0.05, ** \(p<\) 0.01). Data are the mean of four replicate measurements. 4-HBA = 4-hydroxybenzoic acid; 4-HPA = 4-hydroxyphenylacetic acid  
\end{table} 
Table 6: Phenolic acid analysis of adjunct and control beers. Higher alcohols such as n-propanol, isoamyl alcohol and isobutanol can create strong, pungent aromas in beer at high concentrations (>300 mg/L) and can contribute to beer flavour by intensifying alcoholic perception and imparting a warm mouthfeel [20; 39]. Aromatic alcohols such as tryptophan and tyrosol are considered to impart undesirable flavours to beer [40].