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Measuring barley kernel colour and size to predict end use malt quality



Results and discussions - Kernel size and malt quality

The value of 1000 kernel weight for predicting potential malting quality was further investigated with the 24 plum and 24 intermediate samples that were composited from port samples. Kernel weight was found to correlate very significantly with both steep-out moistures and malt extract when the intermediate and plump samples were analysed statistically together. However, the plots of these relationships (Figure 1) indicated that such comparisons were inappropriate given the two distinct populations, intermediate versus plump samples.

Figure 1. Relationships, for both plump and intermediate samples, of 1000 kernel weight versus steep-out moistures (A) and of 1000 kernel weight and malt extract (B)

Figure 1. Relationships, for both plump and intermediate samples, of 1000 kernel weight versus steep-out moistures (A) and of 1000 kernel weight versus malt extract (B)

Figure 2. Relationships, for intermediate samples only, of 1000 kernel weight versus steep-out moistures (A) and of 1000 kernel weight and malt extract (B)

Figure 2. Relationships, for intermediate samples only, of 1000 kernel weight versus steep-out moistures (A) and of 1000 kernel weight versus malt extract (B)

Therefore, statistical comparisons of 1000 kernel weight with extract and steep-out moistures were done independently for intermediate and plump samples (Figure 2 and Figure 3). Thousand kernel weight correlated well with steep-out moistures for the intermediate kernels but insignificantly for the plump samples. In contrast, the relationship with malt extract was highly significant for the plump material but insignificant for the intermediate samples.

In conclusion, 1000 kernel weight provided information on steeping requirements but only for intermediate kernels. In contrast, 1000 kernel weight of plump barley kernels gave an indication the potential malt extract in the final product. SKCS kernel diameter and weight showed similar relationships with steep-out moisture and malt extract but correlation coefficients were slightly lower (data not presented).

Figure 3. Relationships, for plump samples only, of 1000 kernel weight versus steep-out moistures (A) and of 1000 kernel weight and malt extract (B)

Figure 3. Relationships, for plump samples only, of 1000 kernel weight versus steep-out moistures (A) and of 1000 kernel weight versus malt extract (B)

The effect of kernel size on malt quality was further investigated with the SKCS. The plump port samples (n=24) were analysed with the SKCS for kernel weight and diameter and compared to the malt quality.

Three sizing methods, 1000 kernel weight, SKCS kernel diameter and SKCS kernel weight, were compared to each other and to the percentage of plump kernels in the original samples. All four parameters correlated highly significantly with one another (Table 6) but as would be expected, coefficients between 1000 kernel weight and SKCS mean kernel diameter and weight were higher than correlations with kernel plumpness. Thousand kernel weight and SKCS mean kernel diameter and weight all showed very similar correlations with several barley parameters. Correlation coefficients indicated a tendency for large kernels to have less protein but more moisture. There was also an indication that large kernels had poorer germination properties.

Several malt quality parameters also showed significant correlations with 1000 kernel weight and SKCS mean kernel diameter and weight. Coefficients indicated, as expected, that larger kernels produced more malt extract which would explain the positive correlation between size and viscosity, extract being a major contributor to viscosity. Large kernels were also somewhat less modified during malting, supporting the plump/intermediate experiment, as indicated by positive correlations of size on ß-glucan and negative coefficients with friability. Kernel size had no effect on diastatic power for the samples tested. There was some tendency for larger kernels to have less alpha-amylase which may have been related to the poorer modification in the large kernels as alpha-amylase was highly correlated, negatively, with ß-glucan (r=-0.74***).

Table 6. Correlation coefficients between kernel size indices and malt quality parameters (n=24)
  Plump kernels 1000 kernel wt SKCS Mean kernel diam SKCS Mean kernel wt SKCS St Dev kernel diam SKCS St Dev kernel wt
*, **, *** coefficients significant at the: p<0.05, p<0.01 and p<0.001 levels, respectively
1000 kernel weight 0.85*** 1.00        
SKCS Mean kernel diameter 0.88*** 0.95*** 1.00      
SKCS Mean kernel weight 0.84*** 0.96*** 0.94*** 1.00    
SKCS Standard Deviation kernel diameter 0.80*** 0.86*** 0.90*** 0.79*** 1.00  
SKCS Standard Deviation kernel weight 0.64*** 0.68*** 0.80*** 0.59** 0.84*** 1.00
Barley protein -0.38 -0.52** -0.48* -0.49* -0.51** -0.42*
Barley moisture 0.75*** 0.60** 0.73*** 0.55** 0.76*** 0.70***
Germination energy (4 mL) -0.41* -0.34 -0.43* -0.31 -0.46* -0.33
Germination index (4 mL) -0.66*** -0.59** -0.65*** -0.62*** -0.67*** -0.42*
Steep-out moisture 0.31 0.13 0.10 0.10 0.10 0.11
Malt extract 0.70*** 0.82*** 0.80*** 0.79*** 0.76*** 0.68***
Soluble protein -0.01 0.05 0.09 -0.03 0.10 0.15
ß-Glucan 0.30 0.40* 0.49* 0.38 0.57** 0.63***
Viscosity 0.50** 0.62*** 0.67*** 0.59** 0.66*** 0.66***
Diastatic power 0.00 0.03 0.08 0.01 0.08 0.14
α-Amylase -0.37 -0.34 -0.40* -0.33 -0.49* -0.41*
Wort colour 0.36 0.35 0.35 0.31 0.30 0.25
Friability -0.35 -0.31 -0.40* -0.28 -0.47* -0.38