Determination of the proportional composition of grist fractions through sieve analysis
Malt grist, grist from adjuncts
The extract yield in the brewhouse is highly dependent on optimal milling of the malt or other grain. The composition of the brewery grist should therefore be monitored on a regular basis.
The sieve analysis is performed on a sample of brewery grist of a known weight with a shaking device containing a set of sieves (according to DIN ISO 3310-1 specifications or a Pfungstädter plansifter sieving device).
Determination of iso α-acids and α-acids in beer, beer-based beverages and wort
This method is not suitable for beer, beer-based beverages or wort, which contain saccharin, p-hydroxybenzoic acid ester, salicylic acid or sorbic acid.
These bitter substances are extracted from the acidified sample using iso-octane. Certain disruptive substances are eliminated through washing the extract with acidified methanol. The concentration iso-α-acids as well as α-acids is determined by measuring the absorbance in alkaline methanol at 255 nm and 360 nm.
Simultaneous determination of iso-a-acids and reduced iso-a-acids (rho, tetra, hexa) in beer and beer-based beverages using HPLC
This method is not suitable for beer and beer-based beverages containing a mix of hexa- and iso-products (co-elution).
This method separates iso-α-acids and reduced iso-α-acids (rho, tetra, hexa) chromatographically [2].
The separated compounds are detected spectrophotometrically at 270 nm. Quantification is performed using International Calibration Standards (ICS).
These standards do not contain all of the isomers of a certain type of iso-α-acids. Currently, ICS-I (DCHA-Iso) contains only the trans-isomeric complexes with dicyclohexylamine (DCHA). ICS-R (DCHA-rho) only has the cis-isomers in a complex with DCHA. ICS-T (tetra) comprises both cis- and trans-isomer complexes with DCHA, and ICS-H (DCHA-hexa) includes only cis-isomers with DCHA.
Commercially available hop products contain a greater number of isomers than the standards.
Thus, there are more peaks in the chromatogram than in the corresponding international calibration standards, in particular, with the cis-iso-cohumulone as well as the cis-iso-n-humulone and cis-iso-ad-humulone. The application of this method to these kinds of beers should be conducted with this in mind, since it is not entirely known whether these additional peaks are actually isomers of iso-α-acids.
The method is suitable for the determination of water vapor volatile aroma compounds in beer.
Volatile aroma compounds are driven out of the sample through steam distillation. The ethanolic distillate is saturated with NaCl. Potassium hydrogen sulfite is added to separate carbonyl groups that might interfere with the analysis. The extraction of the aroma compounds is performed by shaking out with dichloromethane and the phases separated by centrifuging.
This method describes how to determine iso-α-acids, α-acids and β-acids in isomerized pellets by means of reverse phase high pressure liquid chromatography (RP-HPLC).
Isomerized pellets intended for use in beer brewing or elsewhere in the food industry
The bitter substances in isomerized hop pellets contain a substantial amount of iso-α-acids; however, in addition to these, non-isomerized α-acids and β-acids are also present. In order to determine their content, a specific method is required.
After milling, the substances in question are extracted from the isomerized pellets using a diethyl ether/methanol mixture and a hydrochloric acid solution. The iso-α-acids, α-acids and β-acids dissolved in the ether phase are separated using reversed-phase high-performance liquid chromatography (RP-HPLC) and an elution gradient. They are then measured spectrophotometrically at wavelengths of 270 nm (iso-α-acids) and 314 nm (α-acids and β-acids).
Hop products with isomerized or reduced iso α-acids intended for use in beer brewing or elsewhere in the food industry
Hop products with isomerized or reduced iso α-acids are dissolved with methanol. The bitter acids are separated through reverse phase high-pressure liquid chromatography (RP-HPLC) and isocratic elution. They are then measured at a wavelength of 270 nm.