DETERMINATION OF EXTRACT AND COLD WATER EXTRACT IN MALT BY MEANS OF THE REFRACTOMETER

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Abstract
Measurements of refractive index instead of specific gravity can be used for extract and cold water extract determinations on pale malts. Coloured malts give less satisfactory results and the method is inapplicable to black malts. Regression equations have been developed showing a straight-line relationship between the refractive index of the solution and the extract or cold water extract of the malt. The differences between the figures found by the specific gravity and the refractive index methods are small, but indicate that the latter is a little less accurate than the former, but this is out-weighed in routine work by the saving of time achieved. A study of the precision of the method shows that an immersion refractometer reading to the fifth place is essential, the Abbé instrument, reading to the fourth place only, being insufficiently precise. Temperature needs close control, a rise of 0·1° C. corresponding to a fall of about 0·6 lb. of extract or about 0·07% of cold water extract.

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