Determination of the original gravity, alcohol and extract content using an oscillating U-tube density measuring device and an alcohol sensor in beer or beer-based beverages
Aside from the density, the alcohol concentration is also directly measured with an alcohol sensor. This is carried out using catalytic combustion. In a measured stream of air, alcohol vapor rises countercurrent to the beer flowing downwards. The alcohol vapor is oxidized at the sensor and the resultant heat is measured by means of a resistive circuit. This correlates with the concentration of alcohol in the beer. According to Tabarié’s equation, the relationship between the specific gravity of beer, its alcohol content and real extract content can be calculated as follows:
\(\rho_{\text{beer}} = \rho_{\text{alcohol}} \space + \space \rho_{E_R} \space – \space \rho_{\text{water}}\)
\(\text{SG}_{\text{A20/20 beer}} = \text{SG}_{\text{A20/20 alcohol}} \space + \space \text{SG}_{\text{A20/20}}E_R \space – \space \text{SG}_{\text{A20/20 water}}\)
\(\text{SG}_{\text{A20/20 alcohol}} = 1.000\)
Determination of the correct Velcorin® dosage
flavored beverages, liquid tea concentrate, fruit wine, non-alcoholic wine
DMDC (Velcorin®) is used for the cold sterilization of non-alcoholic beverages. It essentially kills yeasts, bacteria and molds, with little effect on mold spores or yeast ascospores. Certain species of Lactobacillus possess an elevated resistance to Velcorin®.
There should be fewer than 500 microbes/cm3 at the time the dosage is added.
According to the EU guideline EG 1129/2011 [1], up to 250 mg/l DMDC may be added to flavored non-alcoholic beverages, non-alcoholic wine and liquid tea concentrates.
Dimethyl dicarbonate (Velcorin®) quickly dissociates in aqueous solutions almost completely to carbon dioxide and methanol. In addition, small amounts of ethyl methyl carbonate are formed through the reaction of DMDC with ethanol, which can be detected through GC-MS analysis techniques [2]. The amount of DMDC added to a beverage can be determined by measuring the content of EMC and ethanol. The Velcorin® dosage can be checked by measuring the amount of methanol quantitatively using GC analysis; however, the initial amount of methanol present in the product prior to adding Velcorin® must be determined.
H2O + C4H6O5 (DMDC) → 2CH3OH + CO2
250 mg Velcorin → 119.5 mg methanol + 164.1 mg carbon dioxide
C2H5OH + C4H6O5 (DMDC) → C4H8O3 + CH3OH+ CO2
Determination of sorbitol by ion chromatography and pulsed amperometric detection
This method is suitable for fruit juices and other non-alcoholic beverages.
The sugar alcohols are separated using a strongly alkaline eluent and ion exchange column and detected and quantified electrochemically using a pulsed amperometric detector (PAD).
By applying a potential, the ions are oxidized at a gold electrode and induce a measurable charge. To prevent the electrode from being occupied in a very short time, the potential is then reversed to reduce and release the ions from the electrode.
The method is suitable for beer brewed to any original gravity or to any alcohol content.
Higher alcohols and esters in beer are determined by gas chromatography using the headspace method, e.g., the volatile compounds are transferred from the gas space in the sample vial to the GC system for analysis. The method is suitable for beer brewed to any original gravity or to any alcohol content.
Determination of ethanol by enzymatic means
Suitable for beers, non-alcoholic beers, reduced-alcohol beers, beer-based drinks, NAB, juice, beverages.
Ethanol is oxidized by nicotinamide adenine dinucleotide (NAD) in the presence of the enzyme alcohol dehydrogenase (ADH) to acetaldehyde:
Ethanol + NAD+ \(^\underleftrightarrow{Al-DH} \) acetaldehyde + NADH + H+
The equilibrium of this reaction favors the side with ethanol and NAD. In an alkaline medium and through removal of the acetaldehyde produced, the equilibrium can be shifted to favor the substances on the right side of the equation. Acetaldehyde is quantitatively oxidized to acetic acid in the presence of aldehyde dehydrogenase (Al-DH):
Acetaldehyde + NAD+ + H2O \(^\underleftrightarrow{Al-DH} \) acetic acid + NADH + H+
The amount of NADH produced in the reaction is equivalent to half of the amount of ethanol and is measured photometrically due to its absorption at wavelengths of 334, 340 or 365 nm.
Specificity of the determination [1]
The influence of aldehydes and ketones is eliminated by the order of reagent addition during the test. Methanol is not converted due to unfavorable KM values (Michaelis-Menten constant) of the enzymes used. n-propanol and n-butanol are quantitatively converted under test conditions, higher primary alcohols lead to sample-dependent creep reactions. Secondary, tertiary and aromatic alcohols do not react. Glycerin does not interfere with the test even at higher concentrations.
The method is suitable for beer brewed to any original gravity or to any alcohol content.
Volatile compounds in beer are concentrated through distillation and extracted with dichloromethane. The solvent phase is analyzed with a gas chromatograph. The linearity of the detector and the determination of the concentrations of analytes in the sample are achieved by using multiple concentration levels within the relevant range and through evaluation of the relative area under the peaks.