Whole hops intended for use in beer brewing or elsewhere in the food industry
Evaluation of the appearance of hop cones is performed through visual inspection and sensory assessment.
This method describes the conditions under which sensory analysis should be carried out.
beer, beer-based beverages, non-alcoholic beverages, mineral water
One of the basic prerequisites for properly conducting sensory analysis is the utilization of meaningful evaluation forms.
Determination of formic acid by enzymatic means
This analysis is suitable for wort, beer, beer-based beverages and NAB.
Formic acid can be found in beer in small quantities, and it is also formed by contaminating bacteria, for example, by lactic acid bacteria (rods).
In the presence of the enzyme formate dehydrogenase (FDH), the formic acid created in this reaction is quantitatively oxidized to bicarbonate by nicotinamide adenine dinucleotide (NAD):
HCOO- + NAD+ + H2O \(^{\underrightarrow{FDH}}\) HCO3- + NADH + H+
The amount of NADH formed during the reaction is equivalent to the amount of formic acid and can be determined photometrically based on its absorbance at 334, 340 or 365 nm.
Oxalic acid (oxalate) is transformed into formic acid and CO2 in this reaction catalyzed by the enzyme oxalate decarboxylase (Ox-DC):
Oxalic acid \(^{\underrightarrow{Ox-DC}}\) formic acid + CO2
The quantity of NADH produced during the reaction is equivalent to the amount of formic acid and is determined photometrically owing to its absorption at 334, 340 or 365 nm. In preparation for this test, the free formic acid present in the solution is determined along with the oxalic acid. Each are accounted for in the blank.
Turbidity measurement in beer
If a beam of light strikes a particle in a liquid, the light is scattered. This phenomenon is referred to as turbidity. In measuring turbidity during the lautering process, it has been shown that only light scattered in a forward direction should be measured to achieve a meaningful correlation between the concentration of solids and the measurement value. Measurements performed at a 90° angle do not correlate with the amount of solids in wort due to particle size and dependence on color. In addition to the amount of scattered light, the absorption (light transmission) is also measured. The utilization of dual beams eliminates disruptive parameters such as color, lamp age and window fouling.
For monitoring filter efficacy, measurements employing forward scattered light are advantageous (measured at an angle ranging from 11 to 25°).
With a suitable turbidity measuring device, the visual impression of turbidity is quantified.
beer
As with the DLG score sheet, the individual criteria are assessed on a five-point scale. The criteria judged in the evaluation represent a combination of factors pertaining to the assessment of quality (purity of aroma, purity of flavor, quality of bitterness, overall quality) and intensity (bitterness, hop aroma, fullness, liveliness). It is important to note that with reference to fullness, an optimum score is 3 or 4.
Enrichment of the PAH is performed using solid phase extraction. The extract is obtained from the sample through separation with high performance liquid chromatography on the appropriate stationary phases under isocratic conditions. Detection is conducted with a fluorescence detector. The determination is quite sensitive because these polycyclic aromatic hydrocarbons possess substantial fluorescence properties. Since the fluorescence characteristics of these substances are substance-specific, they are determined using two spectra, the excitation and emission spectra. Thus, selective detection is possible. Through recognition of the specific spectra for each substance and the means of detection at the appropriate wavelengths, maximum sensitivity and selectivity are attainable.