Determination of the viscosity of beverages using a micro-viscometer.
Wort, Beer, Mixed beer beverages, Non-alcoholic soft drinks, Juices, Beverages in general
The measuring principle of the micro viscometer is based on the Höppler "Falling Ball Viscometer". A sphere of known dimension rolls through a closed capillary inclined at a defined angle. Inductive sensors detect the ball over a precisely defined distance of approx. 100 mm or 25 mm. The rolling time is measured by the device and used for dynamic viscosity calculation. The temperature is precisely controlled by thermoelectric Peltier elements and checked by a Pt100 temperature sensor. A temperature accuracy of ± 0.02 °C and a repeatability of ± 0.005 °C can be achieved.
The gelatinization temperature can be determined using a rotary viscometer (e.g., Amylograph or Viscograph, Brabender GmbH & Co. KG, Germany [4] or a Rapid-Visco-Analyser, RVA, Perten Instruments, a PerkinElmer Company, USA [8]).
A suspension consisting of a finely ground sample and water is produced, whose precise mixing ratio should correspond to the analysis protocol for the adjunct in question. However, since for many cereals and pseudocereals no official analysis protocol exists, the initial weight for the adjuncts listed in table 2 has been determined empirically [3].
Once the suspension is prepared it is attempered according to a pre-programmed temperature/time program, and the viscosity is determined on a continuous basis by means of a rotor and a rotary torque measurement (fig. 1). When gelatinization begins, an increase in the viscosity is registered, and the corresponding sample temperature is defined as the gelatinization temperature. The standard evaluation criterion (PT) is a viscosity increase of at least 24 cP (≙ mPas) within six seconds.
Malt intended for use in beer brewing or elsewhere in the food industry
While α-amylase is active in a gelatinized solution of amylopectin, the viscosity of the solution is constantly dropping due to the degradation of the starch molecules, which can be tracked using a rotational viscometer. The change in the reciprocal of the specific viscosity serves as a measure for the activity of α-amylase.
Malt intended for use in beer brewing or elsewhere in the food industry
Through the action of endo-β-glucanase on a β-glucan solution, the viscosity of the solution continuously decreases, due to the degradation of the substrate molecules, which is measured using a rotary viscometer. The change in the reciprocal of the specific viscosity is a measure for the activity of endo-β-glucanase.
Determination of the viscosity of beverages
wort, beer, beer-based beverages, NAB, juice, beverages in general
Capillary viscometers measure the kinematic viscosity of Newtonian fluids, unlike falling ball and the rotational viscometers, which directly measure the dynamic viscosity. However, with values for the kinematic viscosity and the density of the test liquid, the dynamic viscosity can be calculated.
The time required for a volumetrically defined amount of fluid (the volume between two marks on the tube of the viscometer) to flow through a capillary of a defined length is measured.
1 square meter per second of a homogenous fluid with a dynamic viscosity of 1 Pa × s and a density 1 kg/m³
The unit for expressing kinematic viscosity (the relationship of viscosity to density = viscoplasticity) is 1 m²/s = 106 mm²/s
The kinematic viscosity is expressed as 1 square meter per second of a homogenous fluid with a dynamic viscosity of 1 Pa × s and a density 1 kg/m³.
Determination of glucose and fructose by enzymatic means
Glucose and fructose are phosphorylated by the enzyme hexokinase (HK) and adenosine 5'-triphosphate (ATP) to glucose 6-phosphate (G-6-P) and fructose 6-phosphate (F-6-P):
Glucose + ATP \(^{\underrightarrow{HK}}\) G-6-P + ADP
Fructose + ATP \(^{\underrightarrow{HK}}\) F-6-P + ADP
In the presence of the enzyme glucose-6-phosphate dehydrogenase (G6P-DH), G-6-P is oxidized from nicotinamide adenine dinucleotide phosphate (NADP) to gluconate-6-phosphate. Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is formed:
\(\text{G-6-P}\hspace{0.2em}+\hspace{0.2em}\text{NADP}\hspace{0.8em}^{\underrightarrow{\text{G6P–DH}}}\hspace{0.8em} \text{glucanate-6-phosphate} + \text{NADP}+\text{H}^+\)
The amount of NADPH formed during the reaction is equivalent to the amount of glucose. NADPH is a measurand and is determined based on its absorbance at 334, 340 or 365 nm.
After the reaction is complete, F-6-P is converted to G-6-P by phosphoglucose isomerase (PGI):
F-6-P \(^{\underrightarrow{PGI}}\) G-6-P
G-6-P reacts in turn with NADP to form gluconate-6-phosphate and NADPH. The additional amount of NADPH formed is equivalent to the amount of fructose and is determined photometrically based on its absorption at 334, 340 or 365 nm.