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

Results and discussions - Kernel plumpness and malt quality

Size of barley kernels was found to have a significant effect on end use malting quality. Twenty-four samples of intermediate sized kernels, from composite of port samples, showed significantly poorer malt quality than the corresponding plump samples (Table 5). Smaller kernels had significantly higher levels of grain protein while germinative index was significantly poorer in these samples. As a result of higher levels of protein and thinner kernels, intermediate sized kernels had significantly lower levels of malt extract than plump samples.

Table 5. Differences in malt quality between intermediate kernels (screened >5/64" slotted & < 6/64" slotted) and plump kernels (screened >6/64" slotted)
Kernel Size Plump Kernels Intermediate Kernels
a, b, c row means with different superscripts, differ significantly (p<0.01) based on Duncan's Multiple Range Test
Inspector's colour 3.0 3.0
Barley protein, % 12.5 b 14.0 a
Germination energy (4 mL), % 98 97
Germinative index (4 mL), % 9.3 a 9.0 b
Steep-out moisture, % 45.2 b 49.7 a
Malt extract, % 80.4 a 75.8b
Soluble protein, % 4.95 [b] 5.92 a
ß-glucan, ppm 78 a 31 b
Diastatic power, °L 153 b 170 a
α-Amylase, D.U. 73.9 a 67.8 b
Wort colour, ASBC units 1.89 b 2.80 a
Friability, % 77.4 a 70.9 b

However, despite the poorer germination index, the intermediate kernels were more completely modified, possibly over modified, as indicated by significantly higher levels of soluble protein and significantly lower levels of ß-glucan. The smaller kernel size and higher protein content in the intermediate samples would both have contributed to the better modification. Higher protein can lead to greater production of enzymes, a necessary component of modification. As well, the smaller volume of intermediate kernels would have allowed enzymes and water to move more quickly, and more thoroughly, through the smaller endosperm resulting in greater modification. As a result ß-glucan and protein were more thoroughly degraded in the intermediate samples resulting in the lower levels of ß-glucan and higher levels of soluble protein, the later contributing to significantly darker wort colours.

The plump samples did show significantly higher friability which was unexpected given the better endosperm modification of the intermediate samples. The better friabilities in the plump kernel samples, therefore, suggested modification in the plump samples, while lower than the intermediate samples, was still adequate.

Enzymes levels were also significantly different among the two kernel sizes with the smaller kernel samples having more diastatic power as a result of higher protein levels. However, the plump kernels did show significantly higher levels of alpha-amylase which was hard to explain, although, possibly related to the excessive steep-out moistures in the intermediate sized kernels.

In summary, the plump kernels were obviously of more value with higher levels of malt extract and lower levels of soluble protein. Results suggested, though, that changes to processing, such as less severe steeping and germination, could result in intermediate sized kernels producing a malt with more acceptable quality.