This method evaluates the varietal purity of a lot of barley by means of the HCl test.
Barley intended for the production of malt is to be evaluated on the basis of the characteristics described below.
This test detects the presence of most varieties of two-rowed and multi-rowed winter barley possessing a green aleurone layer. This test is based upon the reaction between HCl and the green pigment, which turns red in its presence.
Determination of the concentration of dissolved carbon dioxide in carbonated beverages in bottles and cans
The total gas pressure in beer is measured after the beer has been forcefully shaken. The carbon dioxide is then bound through the addition of potassium hydroxide. The amount of air in the beer contributes the remaining volume of gas. Once the value for the total pressure has been corrected by subtracting the quantity of air present in the beer, the carbon dioxide can be measured [1].
Determination of dissolved oxygen concentration by electrochemical oxygen sensors with exposed electrodes
The measurement process using a Digox Analyzer works according to the principle of the potentiostatic three-electrode measurement system developed by TÖDT and TESKE and does not require a membrane.
The measuring electrode consists of solid silver, while the counter electrode is made of stainless steel. The reference electrode is composed of silver/silver chloride.
After generating a defined “polarization voltage”, an electrochemical reaction occurs at the measuring electrode, inducing a reduction of the oxygen molecules in the sample.
Measuring electrode (silver):
O2 + 2 H2O + 4 e− → 4 OH− (cathodic process)
Counter electrode (stainless steel):
4 OH− → O2 + 2 H2O + 4 e− (anodic process)
The flow of current as a result of this reaction is directly proportional to the amount of dissolved oxygen in the sample, if the polarization voltage is fixed as close to the level of the diffusion threshold current as possible.
In this case, the relationship can be represented as follows:
I = K × CO2, whereupon K = n × F × A × 1/d
I = sensor current
CO2 = oxygen concentration
F = Faraday constant
n = number of electrons per molecule
A = cathode surface
d = thickness of the “undisturbed layer” along the wall
The thickness of the undisturbed layer along the wall is determined by the hydrodynamic relationships at the measurement electrode and the transportation of oxygen molecules across the boundary layer brought about by temperature-dependent diffusion processes. Both of these clearly defined factors are precisely measured and compensated.
In order to adjust the polarization voltage between the two electrodes, a third electrode, the reference electrode, is employed in Digox measurement devices. This reference electrode remains in contact with the surface of the measuring electrode over a diaphragm in order to prevent mass transfer [1, 2, 3].
Active calibration:
In-line calibration is integrated into the device and is initiated by pressing a button. Taking advantage of Faraday’s Law, an exactly defined amount of oxygen is produced through the electrolysis of water.
I × t = m × F
I = current required for electrolysis
t = time
m = mass, g/mol
F = Faraday constant
The oxygen dissolves in the medium as it flows through and is detected at the measuring cell. The hydrogen liberated during the electrolysis reaction is not relevant for the measurement. The microprocessor monitors the calibration values and carries out any necessary corrective measures. The electrolysis enables the calibration of the device to be carried out under the same conditions and in the same medium as the analysis. Measurement operations are not disrupted during the calibration process [3].
The following applies to Digox 6.1 and all later models: In order to precisely determine the necessary potential for the measurement system, the Digox Analyzer possesses a scanner, which records the product-specific behavior of the medium subject to analysis. This can establish, whether the medium – due to the additives or supplements – must be measured at another potential. In this way, all types of beer-based beverages, non-alcoholic beverages and wine can be analyzed. Moreover, oxygen-reducing substances which can cause the calibration to be inaccurate may also be detected using the calibration scanning process. The device automatically implements the necessary compensative measures with the factors it has determined.
Determination of oxalic acid by enzymatic means
Suitable for malt, wort, beer, beer-based beverages and soft drinks
Oxalic acid is primarily derived from malt. By reacting with the calcium ions in the brewing liquor, haze caused by calcium oxalate can form. These crystals also serve as nucleation sites for the spontaneous and rapid release of carbon dioxide (gushing). The precise determination of oxalic acid is therefore of great importance in brewing technology.
Oxalic acid (oxalate) is oxidized to carbon dioxide and hydrogen peroxide by the enzyme oxalate oxidase.
\(\text{ Oxalate} \hspace{0.5em}^{\underrightarrow{oxalatoxidase}}\hspace{0.5em} H_2O_2\hspace{0.3em}{+}\hspace{0.3em}CO_2\)
In the presence of the enzyme peroxidase (POD), hydrogen peroxide reacts with MTBH (3-methyl-2-benzo thiazolinone hydrazone) and DMAB (3-dimethyl amino benzoic acid to form a blue quinone complex.
\(H_2O_2+MTBH+DMAB\hspace{0.8em}^{\underrightarrow{POD}} \hspace{0.8em} \text{quinone complex} \space + \space H_2O\)
The intensity of the color is proportional to the concentration of the oxalate in the sample and is measured at 590 nm.
Determination of the total acidity through titration
This method is used to determine the total titratable acids in beverages and concentrates.
Titratable acidity represents the sum of the free acids present in a beverage, with the exception of the dissolved carbon dioxide (carbonic acid). In fruit juices and the beverages prepared from them, they usually consist of malic acid, citric acid and tartaric acid.
The titration of the degassed beverage sample (freed from carbonic acid) is carried out potentiometrically using 0.25 mol/l sodium hydroxide solution either to a pH of 7.0 calculated as tartaric acid or to a pH of 8.1 calculated as citric acid.
Determination of acidity or H+ ion concentration of beverages
Suitable for wort, beer, beer-based beverages, non-alcoholic beverages, juices, beverages
The pH value influences the enzymatic degradation processes during mashing and determines the solubility of the proteins, the hop bitters and the coloration during wort boiling. Furthermore, there is a dependence between the pH of the wort and that of the beer prepared from it. Beers with high pH values are more susceptible to chemical-physical turbidity due to inadequate protein coagulation in the brewhouse. Measuring the pH of wort and beer is therefore part of routine quality control.
The pH value is determined electrometrically [1-4].
Determination of pH is always done in the same way for wort, beer, beer-based beverages, NAB, juices and beverages.
Carbonated beverages must be decarbonated before measurement.