Growth tests in beers supplemented with specific chemical substances were conducted to investigate the growth control method of beer-spoilage bacteria. Lactobacillus brevis and Pectinatus ...frisingensis were inoculated into beers in which the pH was set and chemical substances had been added to form a matrix. Supplementation of the beer with hop bitter compounds (iso-α-acids, α-acids, or SO
2
), had an inhibitory effect on the growth of the tested strains in beer. Furthermore, the growth inhibiting compounds had a synergistic effect when used simultaneously. Two-way repeated measures analysis of variance showed that the interaction effects of combinations of iso-α-acids and α-acids in addition to α-acids and SO
2
on the growth of L. brevis and P. frisingensis in beer were highly significant. To verify the contribution degree of pH, iso-α-acids, α-acids, and SO
2
on the growth of L. brevis and P. frisingensis, growth test results using a combination of these factors set at different levels were subject to stepwise regression. The contributions of undissociated α-acids, undissociated SO
2
, and multiplications of undissociated α-acids and undissociated SO
2
were especially high in the control of L. brevis growth. The contributions of pH, undissociated SO
2
, and multiplications of pH and undissociated iso-α-acids were especially high in the control of P. frisingensis growth. The difference in the contributions of antibacterial compounds between L. brevis and P. frisingensis may be due to the difference in the cell wall/membrane structure. Such factorial analysis may be useful for parameter setting in future product designs and process adjustments.
The rate of isomerization of alpha acids to iso-alpha acids (the compounds contributing bitter taste to beer) was determined across a range of temperatures (90−130 °C) to characterize the rate at ...which iso-alpha acids are formed during kettle boiling. Multiple 12 mL stainless steel vessels were utilized to heat samples (alpha acids in a pH 5.2 buffered aqueous solution) at given temperatures, for varying lengths of time. Concentrations of alpha acids and iso-alpha acids were quantified by high-pressure liquid chromatography (HPLC). The isomerization reaction was found to be first order, with reaction rate varying as a function of temperature. Rate constants were experimentally determined to be k 1 = (7.9 × 1011) e (-11858/ T ) for the isomerization reaction of alpha acids to iso-alpha acids, and k 2 = (4.1 × 1012) e (-12994/ T ) for the subsequent loss of iso-alpha acids to uncharacterized degradation products. Activation energy was experimentally determined to be 98.6 kJ per mole for isomerization, and 108.0 kJ per mole for degradation. Losses of iso-alpha acids to degradation products were pronounced for cases in which boiling was continued beyond two half-lives of alpha-acid concentration. Keywords: Humulus lupulus; hop bitter acid; humulone; isohumulone; alpha acid; iso-alpha acid; wort-boiling; isomerization; kinetics; utilization; beer; bitterness
•The correct stereoconfiguration of the bitter acids has been assigned.•Heterogeneous and organocatalysts can be used for the isomerisation of alpha-acids.•Reduction of iso-alpha-acids to ...hexahydro-iso-alpha-acids is feasible in one step.•Alpha-humulene is regioselectively epoxidised.•The chemistry of beta-caryophyllene is governed by its ring strain.
The annual production of hops (Humulus lupulus L.) exceeds 100,000mt and is almost exclusively consumed by the brewing industry. The value of hops is attributed to their characteristic secondary metabolites; these metabolites are precursors which are transformed during the brewing process into important bittering, aromatising and preservative components with rather low efficiency. By selectively transforming these components off-line, both their utilisation efficiency and functionality can be significantly improved. Therefore, the chemical transformations of these secondary metabolites will be considered with special attention to recent advances in the field. The considered components are the hop alpha-acids, hop beta-acids and xanthohumol, which are components unique to hops, and alpha-humulene and beta-caryophyllene, sesquiterpenes which are highly characteristic of hops.
Wort boiling is one of the most energy-intensive steps in beer production because the isomerization of hop alpha-acids (AA) into iso-alpha-acids (IAA) is a time and energy-consuming process. ...Acceleration of this process by hydrodynamic cavitation (HC), created by a Venturi tube cavitation nozzle, at temperatures below the boiling point, has been tested on a pilot scale. The results show that HC accelerated AA isomerization at all temperatures tested (70–90 °C). The highest HC powered isomerization yield was achieved at 90 °C. However, some quality parameters of the wort were not satisfactory (dimethyl sulphide content, hot break) and therefore the process was extended by a final short boil (10 min). This led to a wort comparable to that obtained after the traditional boiling process (100 °C, 90 min) with a simultaneous 33% energy savings.
•Hydrodynamic cavitation (HC) increased the isomerization yield (Y) of hop alpha-acids.•The highest Y was achieved at 90 °C and cavitation number 0.15.•Some quality parameters of wort produced with HC were not sufficient.•Wort boiling (10 min) after HC-assisted wort treatment improved wort quality.•Complete HC-assisted wort treatment resulted in significant (33%) energy saving.
A simple low-cost methodology for assessing beer bitterness using the IBU (International Bitterness Units) scale has been developed. The experimental setup is composed of a UV source, a fluorescent ...material and a digital single-lens reflex camera. The main concept of the method involves estimating the UV attenuation through IBU solution samples, by comparing the resulting fluorescence instead of the direct UV data obtained with a spectrophotometer. This significantly lowers the cost of the IBU measurement, allowing the hop bitterness values to be directly obtained from simple processing of the fluorescence images. For validation purposes, all values were compared to traditional measurements made with a spectrophotometer. A calibration procedure was carried out using samples with different iso-alpha-acid concentrations, which were naturally measured with the traditional IBU methodology. Finally, for illustrating the application of the novel method, commercial beers were analyzed using the traditional approach and compared with the proposed methodology. The results yielded a root mean square error of predicted samples below 3 IBUs, which demonstrates the potential of the proposed alternative.
•The use of material that fluoresce under UV light, emitting visible light, to evaluate beer bitterness.•The use of inexpensive materials and utilities, such as UV LEDs, paper sheets, digital cameras and freeware softwares.•Good adherence to the ones produced with a spectrophotometer.
A new quantification method for hop-derived bitter compounds in beer was developed. By means of LC-MS/MS operating in the multiple reaction monitoring mode, a total of 26 hop-derived bitter ...compounds, namely, the post-, co-, n-, ad-, pre-, and adpre-congeners of iso-α-acids, α-acids, and β-acids, as well as the prenylflavonoid isoxanthohumol and the chalcone xanthohumol, could be simultaneously detected for the first time in a single HPLC run in authentic beer samples without any cleanup procedures. To compensate for the effect of coextracted matrix components in LC-MS/MS analysis, the so-called ECHO technique was applied for the first time as a suitable strategy for the quantitative analysis of the hop-derived bitter compounds in fresh and stored beer. On the basis of quantitative data, the remarkable instability of α-acids and trans-iso-α-acids was confirmed, and it was observed that the degradation of trans-iso-α-acids during the storage of beer is not dependent from the nature of the alkanoyl side chain of the congeners. In contrast, an increase of the concentrations of β-acids and of the prenylflavonoid isoxanthohumol as well as of the chalcone xanthohumol during the storage of beer was observed.
Hops, Humulus lupulus, contain two major organic acids, humulones, also known as alpha acids, and lupulones, also known as beta acids. These two organic acids are composed of a mixture of three major ...homologs referred to as co-, n-, and ad-. There are also three minor homologs known as post-, pre- and adpre- however these minor hop acid homologs are found in dry hops at very low concentrations, usually less than 0.2%. Today, we report the discovery of a fourth minor homolog for alpha acids and beta acids found in hops called aceto-.
Although there is no indication regarding what type of centrifuge tubes should be used for hop bitterness measurement, this study has demonstrated that the most commonly used tubes (made of ...polypropylene) can cause a significant deviation in the measured bitterness. The traditional procedure for measuring hop bitterness involves extracting a sample of beer with 2,2,4-trimethylpentane (iso-octane) and measuring the absorbance of the organic phase at 275 nm. This procedure was employed to measure the evolution of bitterness during wort boiling and the mentioned interference was first detected, yielding differences as high as 20% between samples processed in plastic and glass tubes. Then, to elucidate that, an experimental comparison using fourteen samples prepared in glass and twenty in polypropylene tubes, was carried out, employing a classical statistical hypothesis test. The results provided a clear indication (with a 99% level of confidence) that the material of the tube can indeed interfere with the bitterness measurement, which is most likely due to the solubilization of the polymer into the organic phase, once plastic polymers absorb in the ultraviolet range.
•Plastic tubes are shown to interfere with beer bitterness measurements.•A proper statistical evaluation of this interference was performed.•A revision to the IBU standard to avoid plastic tubes is suggested.
•Deficit irrigating hops caused reductions in dried hop cone yield.•Hop cone quality was not significantly affected by water stress.•Water productivity increased with increasing water stress.•Deficit ...irrigation should be applied to only already established hop plants.•Using less water led to greater revenue loss than savings in costs of production.
Hop production, like all other water uses in the area, is facing water availability concerns. Deficit irrigation may address water scarcity issues in hop production. This study quantifies the effect of deficit irrigation on hop yield, quality, water productivity and grower profitability. Mt. Hood, Columbus, Chinook and Willamette cultivars were grown under three irrigation levels; 60, 80 and 100% of the crop’s irrigation requirement, using a sub-surface drip irrigation system. Results show that hop plants generally respond to water stress with yield reductions; compared to the 100% irrigation level, the 60% irrigation level caused reductions in total 2-year dry hop cone yield of 30%, 33%, 25%, and 19% for Mt. Hood, Willamette, Columbus and Chinook cultivars respectively, whereas, the 80% irrigation level caused total 2-year yield reductions of 14%, 10%, and 3% for Mt. Hood, Willamette and Chinook cultivars respectively. For Columbus, the 80% irrigation level gave 2% more dry hop cone 2-year total yield than the fully irrigated treatment. Hop cone quality was however not affected; the concentrations of alpha and beta acids were generally similar across all irrigation levels for cultivars for each year of study. The cost of water in Washington State does not vary with changes in water use; only water pumping costs vary with water use. Pumping costs are only 1.5% of the total cost of producing hops in an established yard. As such, savings in pumping costs due to using less water were minimal when compared to the resulting loss in revenue due to yield reductions. Deficit irrigating hops grown under sub-surface drip irrigation system in the Yakima Valley is therefore not economically viable. However, under conditions of water scarcity, high water prices or when there are more profitable alternative uses for the water, deficit irrigation may then be considered. Deficit irrigation though has potential to improve water productivity as observed from the 2012 results. Under the 60% irrigation level, water productivities were 0.42, 0.55, 1.02, and 0.44kg/m3 for Mt. Hood, Willamette, Columbus, and Chinook respectively. Under the 80% irrigation level, water productivities for Mt. Hood, Willamette, Columbus, and Chinook were 0.34, 0.41, 0.95, and 0.45kg/m3 respectively. For full irrigation, water productivities were 0.33, 0.31, 0.84, and 0.37kg/m3 for Mt. Hood, Willamette, Columbus, and Chinook respectively. This study provides production functions for the hop cultivars for forecasting yield quantities under various irrigation amounts.
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