Applicable for all (laboratory) worts
Medium and high molecular weight proteins are precipitated by phosphomolybdic acid. The nitrogen is determined in the filtrate. Therefore, the results express the amount of low molecular weight proteins.
This method describes how to classify barley according to size using a laboratory sieving machine.
Barley intended for the production of malt is to be evaluated on the basis of the characteristics described below.
A barley sample is classified into fractions according to kernel size in a sieving machine containing three sieves with defined slot widths.
Barley intended for the production of malt is evaluated with regard to pre-germination.
Visible pre-germination is evident at the rootlet and is therefore grounds for rejecting a barley lot. However, after the barley is cleaned and the rootlets are removed, the so-called “hidden pre-germination” can be made visible using the staining methods described below.
Kernels suspected of having pre-germinated are boiled for ½−1 min in a 20 % solution of copper sulfate, allowed to remain for 30 min in the hot solution and are subsequently rinsed with water. The acrospire is stained green, making it clearly visible.
The nitrogen/raw protein content of malting barley intended for the production of malt for use in brewing must be determined in advance.
The determination of nitrogen content according to Kjeldahl is divided into the following steps:
a. Digestion of the sample (oxidation of substances H2O, CO2, NH3)
b. Distillation (distillation of NH3 over into a boric acid solution)
c. Titration (determination of the amount of NH3 present in the receiver after distillation)
a. Digestion → 2 NH3 + H2SO4 → (NH4)2SO4
b. (NH4)2SO4 + 2 NaOH → Na2SO4 + 2 NH3 + 2 H2O
3 NH3 + H3BO3 → (NH4)3BO3
c. 2 (NH4)3BO3 + 3 H2SO4 → 3 (NH4)2SO4 + 2 H3BO3
This method describes how to determine not only the variety of barley but whether a lot of barley consists of a mix of varieties.
Barley intended for malt production as well as barley malt
Separation and identification of the protein (hordein) fraction of barley or barley malt by means of gel electrophoresis. The method is suitable for all types of barley, as long as reference substances are available. However, the method cannot be used to identify barley varieties used to produce malt that has been so strongly modified that the protein fraction is almost completely degraded.
This method describes how to classify barley according to size, though this is performed without separating out the half kernels.
Barley malt intended for use in beer brewing or elsewhere in the food industry.
The sieving test represents one of the most important objective physical methods for evaluating malt and can be carried out rapidly and easily. The percentages of total dockage (< 2.2 mm) and that of the kernels belonging to grades I and II can be determined from the results of the sieving test.