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

Materials and methods

All samples were from the 2003 harvest and were AC Metcalfe malting barley that had been commercially selected for malting. Samples were sourced from unloads at port positions or directly from producers. The port-sourced barley samples were collected in Vancouver by the CGC using standard sampling techniques as cars unloaded during the winter and spring of 2004. The producer samples were from submissions to the Barley Development Council's 2003 competition.

The effect of kernel plumpness on malt quality was investigated by separating the port unload samples into intermediate kernels, kernels remaining on a 5/64" slotted screen after passing through a 6/64" slotted screen; and plump kernels, kernels remaining on the 6/64" slotted screen. Samples of each size were malted separately. Composites of samples had to be formed in order to ensure an adequate amount of barley for malting, especially for samples of the intermediate kernels. Four to five unload samples, with similar grades, colour and kernel size, were identified for compositing. The twenty-four composites were mixed after separating samples into intermediate and plump fractions. The 44 competition samples were not mixed but were sized and only plump kernels were malted.

All 68 samples were graded, prior to sizing, (CGC Grading Guide) by one CGC inspector who also visually assessed each sample for colour based on a numerical scale of 1 (good colour) to 6 (poor colour). Colour was determined objectively with image analysis by scanning unsized samples for determination of the RGB, an additive colour model in which equal proportions of red, green and blue can be combined to create white. Thousand kernel weights and analysis with the SKCS were done on the plump and intermediate port composites.

The port and competition samples differed with respect to the homogeneity of kernels within a sample. Not only were composites of the port samples mixed in the laboratory, but unloads in Vancouver were likely blends of barley from different producers. This all contrasted with the competition samples which were from individual producers, thus most likely individual fields, with no compositing in the laboratory. Storage time also differed between the two sets of samples with competition samples being stored at room temperature (ca. 20°C) for 18 months compared to 8 months of room temperature storage for composited port samples.

Samples were malted in a Phoenix Micromalting System with standard 2003 micro-malting conditions (Steeping: 10h wet, 18h dry, 8h wet, 12h dry @ 13°C; Germination: 36h @ 16°C, 60h @ 15°C; Kilning: 12h @ 55°C, 6h @ 65°C, 2h @ 75°C, 4h @ 85°C).

Grades, kernel plumpness and 1000 kernel weight were determined with methods from CGC's Official Grain Grading Guide. Other barley and malt analyses were performed according to the standard methods of the American Society of Brewing Chemists (ASBC).

Barley analyses included:

  1. Grain protein;
  2. Germination energy, the percentage of kernels growing after 72 hours in 4 mL of water;
  3. Germination index, an indication of uniformity and speed of germination over the 72 hours; and
  4. Steep-out moisture, the percentage of water in barley after steeping, the initial process in malting.

Malt analyses included:

  1. Malt extract (fine grind), a measurement of the proportion of a malt that can go into solution, thus, indicating a malt's beer production potential;
  2. Soluble protein, which is required for adequate foam stability in beer, although, too much soluble protein can result in beer hazes and darker coloured beers;
  3. ß-glucan, viscosity and friability, all indicators of the extent to which the barley endosperm has broken down during malting;
  4. Diastatic power and α-amylase, enzymes that render malt starch soluble during the first phase of brewing; and
  5. Wort colour, an indication of final beer colour.