An instrument for evaluating malt modification using the Calcofluor staining test is described. The "Microfluo" comprises an image acquisition chamber, containing a video camera with white and ultraviolet lamps and light intensity sensors, connected to a computer controlled image digitizer and analyser. A sample of 40 grains of malt, half buried in clay blocks and sanded to make half grains, is stained with Calcofluor in the conventional manner, using a second dye (Fast Green) to provide a stronger contrast between the Calcofluor stained areas and the rest of the endosperm, then placed on a turntable in the image acquisition chamber, which takes four images, each covering one quarter of the sample, as it is rotated through a right angle four times. Each quarter image is digitized and divided by the analytical software into ten sections, each holding one half grain, then each of these fields is analysed in turn before proceeding to the next quarter. When the whole sample has been analysed, the results for each grain and for the sample as a whole are calculated and printed out. The instrument must be calibrated using a malt with known modification and homogeneity values. The repeatability figures for modification and homogeneity are much better than those for the manual version of the Calcofluor test (Method 4.13 in the 4th edition of Analytica-EBC). As the intensity of Calcofluor staining varies according to the beta glucan content, the instrument (which is sufficiently sensitive to detect slight differences in fluorescence) can be used to study beta glucan levels in raw barley as well as for evaluating the progress of modification during malting and assessing the quality of the finished malt. Since analysis takes less than 30 minutes, it can be used to check the acceptability of consignments of malt delivered to a brewery.
Keywords : analysis equipment homogeneity malt modification staining