Sweet Wort Research Articles

Barley varieties registered in the Czech Republic after the harvest of 2023

After the 2023 harvest, four varieties of spring barley were registered in the Czech Republic. The malting quality was determined in three varieties. After four years of testing, LG Tuplak was registered. After three years of testing, the spring barley varieties LG Lokal, Sting, and the non-malting variety Ranee were registered. LG Tuplak and LG Lokal showed low activity of proteolytic and cytolytic enzymes and a low level of apparent final attenuation and thus fulfilled the conditionsfor varieties recommended for the production of beer with the protected geographical indication 'České pivo'. The spring barley variety Sting showed very good malting quality. It provided a sweet wort with a rich extract content in malt dry matter (above 83%). Proteolytic modification was optimal to higher in this variety. Cell wall degradation was at an optimal level in the Sting variety. The varieties tested gave clear to opalescent sweet wort.

Barley varieties registered in the Slovak Republic after the harvest of 2023

After the harvest 2023, three varieties were registered in the Slovak Republic after three years of testing: the spring barley variety LG Rhapsody, the two-row winter barley variety Claudia, and the six-row winter barley variety MH Irén. The malting quality was determined for the varieties LG Rhapsody and Claudia. LG Rhapsody gave extract in malt dry matter of 83.2%. Proteolytic modification of this variety was high (Kolbach index 52.3%). The diastatic power (343 WK), the quality of the sweet wort (apparent final attenuation 82.1%), and the cytolytic modification (friability 94% and β-glucan content 60 mg/l) were at an optimal level. In all cases, the variety gave a clear sweet wort. The winter two-row barley variety Claudia gave a sweet wort with an extract of 81.5%. Kolbach index (46.2%) and diastatic power (508 WK) were at optimal levels. The quality of the sweet wort (apparent final attenuation 80.5%) and the cytolytic modification (friability 83% and β-glucan content of the wort 169 mg/l) were at an average level.

Effect of Mashing-in pH on the Biochemical Composition and Staling Properties of the Sweet Wort

Mashing is a decisive brewing step, affecting wort quality. Critical mashing parameters include time, temperature, pH, mash density and oxygen uptake. While the pH-dependent biochemical changes during mashing have been researched, the oxidative processes remain unclear. This work explores the impact of pH conditions during mashing on the biochemical composition and oxidative properties of wort. In laboratory trials, mashing was conducted at different mashing-in pH (4.5, 5.0, 5.2, 5.4, 6.0). The sweet worts were analyzed for extract, fermentable sugars, limit dextrins, amino acids, soluble proteins, polyphenols, color, aldehydes, transition metals, reducing potential, and rate of radical formation. Differences were found in enzymatic activities (particularly proteolysis), color, aldehydes, transition metal ions, the rate of radical formation and the rate of oxygen consumption. Notably, when adjusting the pH at mashing-in, the obtained wort tends to gravitate toward the pH of the unadjusted wort, underscoring its buffering capacity. This was reflected by similar properties of the produced worts, indicating pH playing a lesser role during mashing compared to time/temperature. However, under extreme acidified conditions (pH 4.5 at mashing-in), the produced wort markedly deviates. An intriguing negative correlation between the reducing potential and the content of transition metal ions with the rate of radical formation is discussed.

Study on the effect of malt and decoction mashing on polyphenols and antiradical power of wort

Mashing is one of the key operations in beer brewing. Together with polyphenolic compounds it can affect the quality and stability of beer. In our pilot brewing trials of pale lager (200 L), malts of three barley varieties were compared using either infusion or double decoction mashing. Total polyphenols, anthocyanogens and flavanoids were determined in sweet and hopped wort. Free phenolics were measured by HPLC coupled with coulometric detection. Antiradical power was determined by RC-DCPI, ARA-DPPH and ESR-T150 methods. In this way the influence of mashing method and barley variety on polyphenols and antiradical activity of sweet wort was demonstrated showing that the effect of mashing was stronger (ANOVA). The results showed significantly higher, i.e. by tens of per cent, levels of all polyphenols studied in both the decoction sweet wort and hopped wort. The decoction process resulted in higher levels of the antiradical power, ARA-DPPH (37–47%) and RC-DCPI (25–60%). A cluster analysis partitioned 28 free phenolic compounds in sweet wort primarily by variety and secondarily by mashing. The Malz malt showed a greater increase in polyphenols, free phenolic compounds and antiradical power in the decoction process compared to the Bojos and Sebastian malts. Decoction mashing introduces higher levels of phenolic antioxidants into the beer with the potential to improve the sensory stability of the beer and provide health benefits to the consumer. The different behaviour of malts and barley varieties needs to be better elucidated in further research.

Fate of pesticide residues in beer and its by-products

Sustainable beer production requires a comprehensive assessment of potential hazards such as pesticides in both the finished product and waste streams, as these streams can be used to create high-value by-products. This study presents the tracking of 13 fungicides (azoxystrobin, boscalid, epoxiconazole, fenpropidin, fenpropimorph, fluquiconazole, flutriafol, fluxapyroxad, kresoxym-methyl, spiroxamine, propiconazole, prothioconazole-desthio, and tebuconazole), two insecticides (chlorpyrifos-methyl and deltamethrin), one herbicide (glyphosate), and one growth regulator (mepiquat) through the beer brewing process. Field-treated rye, wheat, and barley samples containing pesticide residues were used as adjunct during brewing. Samples of the beer as well as the by-products (spent grain, spent hops, trub and spent yeast) were collected and extracted with a modified QuEChERS method for pesticide residues analysis using GC-MS/MS and LC-MS/MS. Results show that an average of 58% of pesticide residues are retrieved in the by-products with the highest fraction (53%) recovered in the spent grain, 4% in trub, 1% in spent hops, no residues detected in spent yeast and 9% in the beer. This is consistent with these nonpolar pesticides tending to remain adsorbed to the spent grain during brewing. Glyphosate and mepiquat, the most polar pesticides included in this study, showed a different behavior, with the largest fraction (>80%) being retrieved in sweet wort and transferred to the beer. Processing factors were generated for each pesticide from the adjunct to the beer and to the four by-products.

Grain and malt quality of selected winter barley genetic resources

The present study evaluated the agronomic and malting quality of 18 selected winter barley varieties. The varieties were obtained from the Gene Bank of the Crop Research Institute in Prague-Ruzyně. The varieties were tested under field conditions in three-year trials of basic evaluation. After the harvest, grain was malted and malting quality was determined according to international methods (EBC and MEBAK). The highest extract content was found in the Atlantick variety (80.6%). Proteolytic modification of the varieties Absolut, KWS Ariane and the line QK19/08030A_18 was at an optimal level. Values of diastatic power were high in all varieties, which is typical for winter barley varieties, similarly as low levels of cell wall degradation (friability) and high β-glucan content in the sweet wort. The lowest β-glucan content in the sweet wort was recorded in the two-row winter barley variety KWS Ariane (241 mg/l). Of the six-row varieties, the line QK19/08030A_18 had the lowest β-glucan content in the sweet wort (382 mg/l).

Effect of Wort Boiling System and Hopping Regime on Wort and Beer Stale-Flavor Aldehydes.

The main factor responsible for the sensory aging of beer is the increase in off-flavor aldehydes during beer storage. In pilot brews (200 L) of pale lager beer with different hopping regimes and wort boiling systems, 15 carbonyls were monitored using the GC-MS method. Factor analysis revealed several groups of aldehydes with similar behavior during wort boiling. The concentration of most of them decreased with atmospheric wort boiling and increased with the time and energy-saving pressurized boiling system. Wort clarification was a critical step because of the increase in carbonyl concentration, with the level of most carbonyls being higher in the final wort compared to sweet wort. The hopping regimes only affected the level of 3-methylbutan-2-one in the wort. The concentration of carbonyls decreased significantly (30-90%) during fermentation, except for trans-2-butenal, which increased by 59% on average, likely due to the release from imine complex. The concentration of free aldehydes in the fresh beers was similar for all variants used, but the pressurized wort boiling system could result in lower sensory stability of the beer due to the release of aldehydes from inactive complexes formed during fermentation. This aspect requires further investigation.

Barley varieties registered in the Slovak Republic after the harvest 2022

The study presents the results of technological quality and agronomic characteristics of the spring barley LG Flamenco and winter barley Sonja. These varieties have passed three-year trials within the state varietal trials of the Slovak Republic. At the optimum nitrogen content in unmalted grain, the LG Flamenco variety showed an extract content of 83.2% and the Sonja variety 81.4%. The diastatic power was at the optimum level for both varieties (316 and 411 WK un.). The Kolbach index was at the optimum level (48.3%) for LG Flamenco and 39.6% for Sonja. In the LG Flamenco variety, cell wall degradation was given by a friability value of 88% and a β-glucan content of 192 mg/l. The friability value for the variety Sonja was 82% and the β-glucan content was 193 mg/l. The quality (apparent final attenuation) of the sweet wort was satisfactory for both varieties (81.0%).

Wheat craft beer made from AFB1-contaminated wheat malt contains detectable mycotoxins, retains quality attributes, but differs in some fermentation metabolites

Levels of aflatoxin B1 (AFB1) were measured during the production of wheat craft beer made with wheat malt contaminated with AFB1 (1.23 µg/kg). A wheat craft beer made with non-contaminated wheat malt was produced for comparison purposes. AFB1 was measured after mashing (malt after the mashing process), and in spent grain (spent grains are filtered to collect the wort - remaining sugar-rich liquid), sweet wort, green beer, spent yeast, and in beer. Physicochemical parameters (pH, titratable acidity, color parameters, total soluble solids), sugars, organic acids, alcohols, and phenolics were evaluated after mashing, and in sweet wort, green beer, and beer samples. Density and yeast counts were determined over 120 h of sweet wort fermentation every 24 h. The AFB1 levels in the final beer were 0.22 µg/L, while the spent grains and spent yeasts contained 0.71 ± 0.17 and 0.11 ± 0.03 µg/kg of AFB1, respectively. AFB1 contamination did not influence the final product's physicochemical parameters, density during fermentation, fructose, or glycerol content. Higher yeast counts were observed during the first 48 h of non-contaminated wheat craft beer fermentation, with higher ethanol, citric acid, and propionic acid contents and lower glucose, malic acid, and lactic acid contents compared with beer contaminated with AFB1. Non-contaminated wheat craft beer also had higher concentrations of gallic acid, chlorogenic acid, catechin, procyanidin A2, and procyanidin B1. AFB1 contamination of wheat malt may not affect basic quality parameters in wheat craft beer but can influence the final product's organic acid and phenolic contents. Our findings show that if wheat craft beer is made with contaminated malt, AFB1 can remain in the final product and may pose a risk to consumers.

Barley varieties registered in the Czech Republic after the harvest 2022

After the 2022 harvest, seven new varieties of malting barley were registered in the Czech Republic. After three years of testing, spring barley varieties Ambiana, Gingko, Kimberly, KWS Thalis, LG Ludvik, LG Rhapsody and RGT Proxima were registered. Based on the results obtained, LG Ludvik was recommended for the production of beer with the protected geographical indication 'České pivo'. This variety showed low activity of proteolytic and cytolytic enzymes and low level of final attenuation. The other spring barley varieties (Ambiana, Gingko, Kimberly, KWS Thalis, LG Rhapsody and RGT Proxima) gave sweet wort with extract content in malt dry matter ranging from 82.6 to 84.6%. The varieties Ambiana, Gingko, LG Rhapsody and RGT Proxima had extract contents of more than 83%. Proteolytic modification was high (Kolbach Index above 50%) in the varieties Gingko, LG Rhapsody and RGT Proxima. The β-glucan content in sweet wort below 100 mg/l was recorded in the varieties Gingko and LG Rhapsody. Cell wall degradation (friability 85–94%) and final attenuation(81.7–83.0%) were at optimum levels in Ambiana, Gingko, Kimberly, KWS Thalis, LG Rhapsody and RGT Proxima. Gingko, Kimberly and LG Rhapsody always produced clear sweet wort. Low to zero lipoxygenase activity was found in KWS Thalis.

The buffering capacity of single amino acids in brewing wort

SummaryBuffering capacity (BC) is one of the important quality parameters of wort. In this study, the effect of single amino acids on brewing wort pH and its influence in wort BC were investigated. A beer sweet wort (BSW) was used as a control. A synthetic sweet wort (SSW) and synthetic sweet wort without amino acids (SSWNA) were prepared for a general comparison due to its absence of peptides. BC was conducted by the addition of hydrochloric acid. Results showed that a BSW and a SSW differed in their BC because SSW did not contain small peptides/peptides/polypeptides; SSWNA lost its BC severely due to its absence of nitrogenous compounds. Among all amino acids, arginine, and glutamic acid presented a higher influence in initial pH. However, aspartic acid wort demonstrated the best BC; therefore, this amino acid can be used to control the BC of brewers wort.

Impacts of Adjunct Incorporation on Flavor Stability Metrics at Early Stages of Beer Production

The fresh flavor of a beer brand is one of its most important quality parameters and should be retained as long as possible through shelf-life. Early stages of beer production can have significant impacts on beer flavor stability. The use of cereal adjuncts – either malted or unmalted – is now widespread practice in brewing. This laboratory mashing study investigated the impacts of incorporating common solid adjuncts (corn and rice) at increasing grist percentages (0-50%) on flavor stability indicators measured in wort. Sweet worts were analysed for metal ion levels (ICP-MS), thiol content (RP-HPLC), oxidative stability (EPR spectroscopy), staling aldehydes (HS-SPME-GC-MS), trihydroxy fatty acids (GC-FID), t-2-nonenal potential (GC-MS), color and thiobarbituric acid (TBI). Mashing conditions for each formulation were adjusted in order to achieve target FAN values. Unmalted rice or corn adjuncts significantly reduced the total metal ion content, color, TBI and staling aldehydes in sweet worts at 50% adjunct incorporation (p < 0.05), relative in each case to the respective all-malt control mash. Our findings showed that unmalted rice or corn adjunct incorporation generally improved flavor stability metrics in sweet worts when similar mashing conditions were applied, whilst increasing the length of the ‘protein stand’ in mashing to reach target FAN in general had a negative impact on flavor stability indicators – e.g., wort T150 values significantly decreased in each recipe at 25% and 35% adjunct relative to the 12.5% adjunct brew but increased again at 50% adjunct, presumably due to the prolonged proteolytic stand employed to achieve target FAN content.

Fate and Behavior of Field-Applied Pesticides during Malting and Mashing Processes.

The present work aimed to study the fate of field-applied pesticides during malting and mashing processes. Twenty-four field-collected barley samples were subject to micromalting followed by lab-scale mashing to investigate the carryover of residual pesticides from barley to malt and then from malt to sweet wort. The citrate-buffered QuEChERS sample preparation method was adapted for simultaneous determination of 57 pesticide residues in grain, malt, spent grains, and sweet wort samples using ultra-performance liquid chromatography coupled with tandem mass spectroscopy (UPLC-MS/MS). Residues of four fungicides (fenpropimorph, pyraclostrobin, tebuconazole, and trifloxystrobin) and two insecticides (chlorpyrifos and pirimiphos-methyl), frequently found in the barley samples, were investigated in detail in this study. The carryover percentages of these pesticides to malt, against the concentration of residues in barley grain, ranged from 22% for pirimiphos-methyl up to 78% for fenpropimorph. The results confirm a general rule that residues of pesticides with log P values >2 remain on the malt, but it was found that their transfer potential is more related to its individual physical-chemical properties but does not much correlate to their log P values. In the second part of the study, a noticeable carryover from malt to sweet wort was observed for pyraclostrobin, fenpropimorph, and tebuconazole residues, and these values ranged from 2 to 15%. Moreover, the analysis of pesticide residues in spent grain after mashing revealed that the spent grain samples contain on average once as much pyraclostrobin and tebuconazole residues as the original malt. It was concluded that (1) pyraclostrobin and tebuconazole residues could be incorporated into or associated with macromolecules in barley grain to form "hidden" (bound) forms, and (2) the parent compounds are subsequently released from their hidden forms during mashing.

Copper Binding in Sweet Worts Made from Specialty Malts.

Trace levels of copper can impact the flavor stability of beer. The main source of copper is malt, and the wort copper levels are established during mashing and lautering. This study focuses on sweet worts made from experimental roasted and caramel malts. Potentiometric titrations using ion-selective electrodes combined with electron paramagnetic resonance spectroscopy have been used to investigate Cu(II) binding in worts as well as the impact of Cu(II) ions on the wort oxidative stability. High-temperature treatment during malting decreased Cu(II) binding affinities in the worts, with roasted malt worts having lower affinities than caramel malt worts of similar color and pH. Electron paramagnetic resonance spectra indicated dipeptides as the main Cu(II) chelators. A positive correlation between Cu and free amino nitrogen levels in worts is demonstrated. In dark worts with high rates of radical formation, Cu(II) had pronounced antioxidative effects. In contrast, moderate prooxidative effects were observed when adding Cu(II) to pale worts with inherently low rates of oxidation.

Evaluation of the phytochemical composition and antimicrobial properties of two aromatic plants used in the production of sweet wort and tchapalo, two artisanal beverages from Côte d'Ivoire

The search for new antimicrobial molecules from natural sources is an opportunity to preserve food. The objective of this study is to evaluate the phytochemical composition and antimicrobial properties of the leaves of Adansonia digitata (Bombacaceae) and the bark of Grewia venusta (Tilaceae), two aromatic plants used in the production of sweet must and tchapalo. Phytochemical screening from the aqueous, decocted and methanolic extracts of these plants was performed using standard colorimetric methods. Antimicrobial activity was also evaluated on 21 strains using the well diffusion method. Minimum Inhibitory Concentrations (MIC) and Bactericides were determined respectively by the liquid macro-dilution and agar plating methods. Results showed the presence of tannins, triterpenoids, cardiotonic glycosides and saponins in these extracts. All extracts were active on Staphylococcus aureus ATCC25923 with inhibition diameters ranging from 10.33±1 to 20.3±1.5 mm. The methanolic extracts had the lowest MICs (12.5 mg/mL), with bactericidal and/or fungicidal activity on most of the microbial strains tested. These results confirm the antimicrobial activities of the phytochemical compounds of these plants that could play the role of stabilizer and preservative of sweet wort and tchapalo.&#x0D; La recherche de nouvelles molécules antimicrobiennes à partir de sources naturelles est une opportunité pour conserver les aliments. L’objectif de cette étude est d’évaluer la composition phytochimique et les propriétés antimicrobiennes des feuilles de Adansonia digitata (Bombacaceae) et des écorces de Grewia venusta (Tilaceae), deux plantes aromatiques utilisées dans la production du moût sucré et du tchapalo. Le criblage phytochimiques à partir des extraits aqueux, décoctés et méthanoliques de ces plantes a été réalisé selon les méthodes standards de colorimétries. L’activité antimicrobienne a été également évaluée sur 21 souches en utilisant la méthode de diffusion en puits. Les Concentrations Minimales Inhibitrices (CMI) et Bactéricides ont été déterminées respectivement par les méthodes de macro-dilution en milieu liquide et ensemencement sur milieu gélosé. Les résultats ont montré la présence de tannins, de triterpénoïdes, de cardiotoniques glycosides et de saponines dans ces extraits. Tous les extraits ont été actifs sur Staphylococcus aureus ATCC25923 avec des diamètres d’inhibition allant de 10,33±1 à 20,3± 1,5 mm. Les extraits méthanoliques ont présenté les CMI les plus faibles (12,5 mg/mL), avec une activité bactéricide et/ou fongicide sur la plupart des souches microbiennes testées. Ces résultats confirment les activités antimicrobiennes des composés phytochimiques de ces plantes qui pourraient jouer le rôle de stabilisant et conservateur du moût sucré et du tchapalo.

Retention of Iron and Copper during Mashing of Roasted Malts

Malt is the major source of iron (Fe) and copper (Cu) in wort and beer, and the main uptake of Fe and Cu ions happens during mashing. Past research has indicated that the mineral composition of sweet wort primarily depends on the ion removal rate during mash filtration. In this study, the capacity to remove Fe and Cu during mashing has been evaluated. Each metal was added (50 µM) at the beginning of congress mashings and the final concentrations in sweet wort were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES). There was little to no difference between the samples spiked with Fe and the blanks when using pure pilsner malt, suggesting that there is an efficient binding of Fe in the spent grains. A significant, but not complete, removal was also observed for Cu-spiked samples. Mashing with roasted malt showed decreased removal of Fe while removal of Cu was increased. The effects of addition of high metal concentrations during mashing on the oxidative stability of the sweet wort were evaluated using electron spin resonance (ESR) spectroscopy and oxygen consumption. It was concluded that the spent grains have an important leveling effect on the final Fe and Cu concentrations in sweet wort, which also levels the effects on oxidative reactions.

Evaluation of potential lactic acid bacteria single starter cultures for production of traditional Ivoirian cereal beverages

Twenty-three lactic acid bacteria (LAB) previously isolated from tchapalo process were evaluated as single starter cultures for traditional Ivoirian beverages production. These LAB were inoculated separately into sorghum wort and fermented at 30 °C for 12 h. During fermentations, pH, titratable acidity, and LAB growth were determined. After that, the six better bacteria had been used to produce controlled sour wort, sweet wort and tchapalo. Then, pH, titratable acidity, total soluble solids, and organic acids were analyzed. Their antimicrobial activities also were tested. Within 6 h of fermentation, out of twenty-three bacteria, only six (26.08%) of strains namely L. fermentum strains S6, S42 and S45, P. acidilactici strains S7 and S52 and P. pentosaceus strain S5 accelerated fermentation by dropping of ΔpH to ≥ 1.5 units and increasing of ΔAT to ≥ 0.15%. Lactobacillus fermentum strain S6 carried out his exponential growth rate from 0.18 log CFU/mL to 2.67 log CFU/mL during 2 to 6 h. The sour wort obtained by using of these strains were like those of controls. Tartaric and lactic acids were detected in all the fermented beverages with single starter cultures with a predominance of lactic acid, but their contents varied according to starter cultures. Some sweet wort and tchapalo produced with single starter cultures were able to inhibit the growth of Escherichia coli, Salmonella typhi and Staphylococcus aureus. These six LAB would be used single to improve safety of sweet wort and tchapalo.

Free amino nitrogen in sweet wort made from barley varieties tested in the Czech Republic

The effect of the variety on the free amino nitrogen (FAN) content in wort was studied in the set of 24 varieties grown at four different testing sites for a three-year period. FAN was determined by the EBC 4.10 method. The highest average FAN was exhibited by the variety KWS Amadora (193 mg/l). The content of FAN was mostly affected by the year (24%), followed by the site, (15%); the effect of the variety was the lowest (13%). Nearly 50% of the samples exhibited low FAN, slightly over 40% of the samples had medium FAN and 12% of the samples exhibited high FAN.

Variation in maltose in sweet wort from barley malt and rice adjuncts with differences in amylose structure

Starch from malt and solid adjuncts provides the majority of fermentable sugars for fermentation. However, there is no current data on the variation in starch structure (particularly long chained amylose) and its impact on the final wort composition of fermentable sugars, specifically maltose. This is the first study to report variation in amylose structure from barley malt and rice used as an adjunct and how this impacts the production of maltose. We compared four commercial malts with two rice adjuncts mashes, in solid and liquid additions, with an all-malt mash used as a control. All combinations of malt and rice adjuncts were tested under two grist-to-liquor (G:L) ratios (1:3 and 1:4) in a 65°C ramped mash. After mashing, the wort original gravity and maltose concentration were measured. The commercial malts had different malt quality but very similar gelatinisation temperatures (~65°C). The malts varied in starch and amylose contents but had only minor variations in average amylose chain lengths. The two rice adjuncts also had similar average amylose chains lengths, but quite different amylose contents, and hence different gelatinisation temperatures. The results showed that liquid adjunct mashes had higher original gravity and maltose concentration for both G:L ratios. However, there was no consistent result in original gravity or maltose between G:L ratio or adjunct type, suggesting interactions between each malt and rice adjunct. Knowing amylose chain length could improve understanding of the potential maltose levels of the sweet wort prior to fermentation.

The chemical profiling of fatty acids during the brewing process

Although fatty acids have a beneficial effect on yeast growth during fermentation, their effect on foam and sensory stability of beer is negative. In general, long-chain fatty acids originate from raw materials, whereas short-chain acids are produced by yeast during fermentation. If the concentration of short-chain fatty acids, especially isovaleric and butyric acid, overreaches a sensory threshold, then an unpleasant aroma, such as cheesy or sweaty feet, can be formed in beer. The distribution of fatty acids, from the preparation of sweet wort to the final beer, was studied using chemometric evaluation. Differences were observed between the decoction and infusion system using four barley varieties. Attention was paid to the behavior of short-chain fatty acids, namely isovaleric acid. The concentration of isovaleric acid in commercial beers brewed in infusion and decoction systems was approximately 1.4 and 1.0 mg L-1 , respectively. The same trend was observed in experimental samples (1.3 and 0.5 mg L-1 , respectively). This phenomenon was confirmed experimentally; based on the results, this possibly explains why, during the fermentation, isovaleric acid is coupled with the redox state of yeast cell, which is given by the wort composition (i.e. by the mashing process). The formation of isovaleric acid is not only caused by microbiology infection or by oxidized hops, but also is influenced by the mashing process. © 2018 Society of Chemical Industry.