Effect of unmalted oats (Avena sativa L.) on the quality of high-gravity mashes and worts without or with exogenous enzyme addition

Barley malt is the preferred brewing material these days because of its high extract content and high enzyme activities. However, when substituting malted barley with oats to create a unique beer flavor and aroma, endogenous malt enzymes become the limiting factor. Therefore, the objectives of this study were to evaluate the effect of 10–40 % unmalted oats on the quality of high-gravity mashes/worts and to investigate the limitations of endogenous malt enzymes as well as the benefits of the application of industrial enzymes. The enzyme mix Ondea^® Pro was found to be particularly suitable for mashing with unmalted oats and was therefore used in the present rheological tests and laboratory-scale mashing trials. In order to gain detailed information about the biochemical processes occurring during mashing, the quality of mashes was comprehensively analyzed after each mash rest using standard methods described by Mitteleuropäische Brautechnische Analysenkommission and Lab-on-a-Chip capillary electrophoresis. Mashing with up to 40 % oats resulted in increased mash consistencies, color/pH (20 °C) values, β-glucan concentrations, wort viscosities 12.0 %, and filtration times as well as decreased FAN and extract contents. The application of Ondea^® Pro enormously increased the color of worts despite lower pH values but considerably improved the quality and processability of 30 or 40 % oat-containing mashes/worts. However, the substitution of up to 20 % barley malt with unmalted oats can easily be realized without the addition of exogenous enzymes.     

THE VISCOSITY OF WORTS IN RELATION TO THEIR CONTENT OF β-GLUCAN

A procedure is given for assessing that proportion of wort viscosity which is attributable to β-glucan. Worts obtained from unkilned samples of malt which have been processed for 54 or 72 h show enhanced viscosity. This is principally due to β-glucan although the contribution of other constituents, absent from the wort of fully modified malt, is of significance. Barley variety is shown to have a pronounced effect on wort viscosity. Insoluble β-glucan is brought into solution in mashes at 65° C. The β-glucan isolated from malt which has been inactivated using aqueous ethanol prior to extraction at 65° C, is of higher specific viscosity than that isolated from control worts prepared at the same temperature. The introduction of a rest by mashing initially at 40° C results in the production of wort of lower viscosity, a decrease in the β-glucan content of the wort and a reduction in the specific viscosity of the β-glucan. There is no apparent relationship between the endo-β-glucanase content of the malts and either the viscosity of derived worts or the degree of breakdown of β-glucan which occurred during malting and mashing. Abrasion of barley, which is a factor assisting the distribution of enzymes during malting, acts to reduce wort viscosity.     

Implementation of commercial oat and sorghum flours in brewing

Brewing with commercial flours has the potential to reduce mashing times and improve brewhouse efficiency. At present, however, no studies are available assessing the application of commercial oat and sorghum flours as brewing adjuncts. Therefore, the objectives of this study were to evaluate the quality and processability of mashes/worts produced with 10–90 % oat or sorghum flour as well as to reveal the advantages and limitations of their use as a substitute for barley malt. For these purposes, both flour types were fully analyzed in terms of brewing-relevant characteristics using standard methods, Lab-on-a-Chip capillary electrophoresis, and scanning electron microscopy. Laboratory-scale mashing trials were performed to assess the effect of up to 90 % flour adjunct on mash/wort quality. Equivalent factors were introduced to determine the performance efficiency of different oat/sorghum flour concentrations. Commercial oat flour sourced in Ireland exhibited significantly more protein, β-glucan, and fat, less starch, ash, and polyphenols, as well as a lower starch gelatinization temperature than commercial sorghum flour obtained from the USA. Worts produced with 10–90 % oat or sorghum flour had lighter colors, higher pH values, and lower concentrations of foam-positive proteins as well as free amino nitrogen compared to 100 % barley malt worts. In terms of extract yields, the use of up to 70 % oat flour and 50 % sorghum flour, respectively, has proven economically beneficial. Worts containing up to 70 % oat flour showed a very good or good fermentability, those containing 30–50 % sorghum flour resulted, however, in a lower alcohol production.     

β-GLUCAN AND β-GLUCAN SOLUBILASE IN MALTING AND MASHING

During malting the water-insoluble β-glucan of barley is diminished whilst water-soluble gum is little decreased. The amount of β-glucan surviving into malt depends on variety but barleys rich in glucan give malts with high β-glucan levels. The β-glucan content of barley depends on variety and growth site. β-Glucan solubilase survives mashing and catalyses the release of hemicellulose into solution. There is no correlation between the β-glucan content of malt and the amount released into wort. However, barley adjuncts containing high levels of β-glucan give worts rich in β-glucan. β-Glucan dissolution in mashing is dependent on time, temperature, grist particle size and liquor: grist ratio. Use of adjuncts derived from barley contribute relatively more β-glucan in wort, coinciding with reduced rates of wort separation, but these can be increased by using a β-glucanase produced by growing the fungus Trichoderma viride on spent grains.     

Brewing with 100% Oat Malt

Oats are a cereal with beneficial nutritional properties and also unrealized brewing potential. Furthermore, oats can be tolerated by the majority of people who suffer from celiac disease. Malting of oats produced a malt, which was found suitable for brewing a 100% oat malt beer. The mashing regime, designed by using mathematical modelling, was successfully transferred to a pilot scale plant. The improved lautering performance of oat malt was due to its higher husk content, which also led to a lower extract content in oat wort when compared to barley wort. The protein profile of oat wort, as measured by using Lab‐on‐a‐Chip analysis, revealed that there was no significant difference in the protein profile between oat and barley wort. The fermentation of oat and barley worts followed the same trend; differences could only be seen in the higher pH and lower alcohol content of the oat beer. The flavour analysis of oat beer revealed some special characteristics such as a strong berry flavour and a lower amount of staling compounds when forced aged. This study revealed that it was possible to brew a 100% oat malt beer and that the produced beer was comparable to a barley malt beer.     

EFFECTS OF CULTIVAR AND ENVIRONMENT ON β-GLUCAN CONTENT AND MALTING QUALITY OF TURKISH BARLEYS

Eight barley cultivars grown under the same agronomic conditions and samples of Tokak cultivar grown at six different sites of Turkey were used in this study. There were significant differences among the barley cultivars and growing locations in terms of β-glucan content (p<0.05). Among malt quality criteria tested for the 8 barley cultivars; friability, viscosity, Kolbach index and extract difference showed significant correlations (p<0.05) with the total β-glucan content. Similar correlations were also observed between the malt quality criteria (Kolbach index and extract difference) and β-glucan contents for the Tokak samples grown at different sites.     

Brewing with up to 40% unmalted oats (Avena sativa) and sorghum (Sorghum bicolor): a review

Beer production with up to 40% unmalted cereals such as barley, wheat, rice and maize is legally allowed and thus practised in many European countries. The use of oats and sorghum as brewing adjuncts has great potential for creating new beer types/flavours and saving costs. In contrast to oats, sorghum is not as well known within Europe; however, its versatility makes it a very promising crop for exploitation in these temperate‐zone regions. This review describes the brewing‐relevant characteristics of unmalted oat and sorghum grain, investigates the role and properties of endogenous/exogenous enzymes during mashing, discusses the processability/quality of mashes, worts and beers produced with up to 40% oat or sorghum adjunct, and examines the effectiveness/limitations of endogenous enzymes as well as the benefits of the application of exogenous enzymes. Copyright © 2014 The Institute of Brewing & Distilling     

MICROBIAL ENZYMES AND THEIR EFFECTS ON EXTRACT RECOVERIES FROM UNMALTED ADJUNCTS

Radial diffusion tests were used to detect β-glucan-, starch-, protein-, pentosan- and triglyceride-degrading enzyme activities in a variety of commercial enzyme preparations. Some implications of the presence of unexpected enzymes in particular preparations are discussed. A series of laboratory mashes were made with grists of milled barley, extruded barley, and extruded wheat, using various enzyme additions and temperature-time programmes. In addition a limited number of experiments were made with pale ale barley malt, and wheat flour pellets. Extract yields varied from acceptable to outstandingly good. The most intensive mashing system, with enzyme supplementation, increased the extract yield of an all-malt mash by 3·9% relative to the control mashing programme. Some worts were evaluated for Total Soluble Nitrogen (T.S.N.), Free Amino Nitrogen (F.A.N.) and viscosity. Slow wort-filtration rates occurred in some mashes although the viscosities of the worts from these mashes were low. This problem did not occur in any of the samples intensively mashed over a 5 h period. The results apparently exclude the possibility that a simple, reliable technique for estimating the extract yields of adjuncts could be devised, using these enzyme preparations.     

α-GLUCOSIDASE ACTIVITY OF SORGHUM AND BARLEY MALTS

Sorghum malt α-glucosidase activity was highest at pH 3.75 while that of barley malt was highest at pH 4.6. At pH 5.4 employed in mashing sorghum malt α-glucosidase was more active than the corresponding enzyme of barley malt. α-Glucosidase was partly extracted in water but was readily extracted when L-cysteine was included in the extraction buffer, pH 8. Sorghum malt made at 30°C had higher α-glucosidase activities than the corresponding malts made at 20°C and 25°C. Nevertheless, the sorghum malts made at 20°C and 25°C produced worts which contained more glucose than worts of malt made at 30°C. Although barley malts contained more α-glucosidase activity than sorghum malts, the worts of barley had the lowest levels of glucose. The limitation to maltose production in sorghum worts, produced at 65°C, is due to inadequate gelatinization of starch and not to limitation to β-amylase and α-amylase activities. Gelatinization of the starch granules of sorghum malt in the decantation mashing procedure resulted in the production of sorghum worts which contained high levels of maltose, especially when sorghum malt was produced at 30°C. Although the β-amylase and α-amylase levels of barley malt was significantly higher than those of sorghum malted optimally at 30°C, sorghum worts contained higher levels of glucose and equivalent levels of maltose to those of barley malt. It would appear that the individual activities of α-glucosidase, α-amylase and β-amylase of sorghum malts or barley malts do not correlate with the sugar profile of the corresponding worts. In consequence, specifications for enzymes such as α-amylase and β-amylase in malt is best set at a range of values rather than as single values.     

Effects of arabinoxylan solubilization on wort viscosity and filtration when mashing with grist containing wheat and wheat malt

Arabinoxylans are partially water-extractable, high-molecular-weight polymers that contribute to the problems of viscosity and membrane filterability during beer brewing. These problems are more pronounced when wheat and wheat malt are used as adjuncts due to their higher arabinoxylan contents and higher molecular weights. This paper aimed at investigating the effects of mashing temperature, time, grist size and liquor:grist ratio on the solubilization of arabinoxylans. Results indicated that increasing the mashing temperature generally increased the amount of arabinoxylans released into the wort. When greater proportions of wheat or wheat malt were used as adjunct, higher arabinoxylan contents in the final wort were observed. The more finely ground the grist, the more were arabinoxylans released into the wort. When more diluted mashes were used, more efficient solubilization of arabinoxylans was observed. The effects of arabinoxylan content and β-glucan content on the wort viscosity were also examined using a General Linear Model (GLM). There was a good correlation (R² = 0.98) between wort viscosity and its arabinoxylan and β-glucan contents.     

Sensitivity Analysis in Predictive Models for assessing the Level of β-Glucan in Oats and Barley Cultivars Using Meta-Models

Oats and barley β-glucans are well-known for their many health benefits; this has encouraged the food industry to develop new functional foods containing oats and barley. This study aims to develop an advanced sensitivity analysis to analyse and evaluate the most significant model inputs contributing to uncertainty in assessing the level of β-glucan content in harvested oat and barley grains. Two methodologies, nominal value and regression method sensitivity analysis, were adopted. The nominal sensitivity analysis highlighted that cultivar selection is the predominant factor with a correlation coefficient 0.66 for hulled oats and barley cultivars, whereas the correlation was 0.80 and 0.77 for naked oats and hull-less barley, respectively. Advanced sensitivity analysis using regression modelling highlighted that cultivar selection, storage days and germination time (days) were the most important parameters in both the oats and barley model. Regression analysis using the response surface methodology shows that prediction models were found to be significant (P < 0.0001) with low standard errors and high coefficients of determination (R ²  > 0.94). This study shows that regression modelling is an effective tool to highlight the effect of key input variables and their interactive effects on the predictive response of β-glucan in harvested oats and barley cultivars.     

Brewing Beer with Sorghum

Research reports on extracts, proteins, total nitrogen and free amino nitrogen content of sorghum malt and worts obtained from mashes indicate that sorghum is potentially an alternative substrate for conventional beer brewing in the tropics. Remarkable variations in biochemical characteristics among different sorghum cultivars affect their optimal malting conditions. Factors such as temperature and time of steeping and germinating of grains with their intrinsic enzymic activities, and kilning temperature determine the quality of malt. Further works on mashing, viscosity and fermentability of worts as well as the character of the resulting beers, such as alcoholic content, colour, taste and specific gravity tend to confirm the status of sorghum as a credible substitute for barley in beer brewing. This review reports on progress made in the use of sorghum for brewing beer.     

THE USE OF EXTRUDED BARLEY,WHEAT AND MAIZE AS ADJUNCTS IN MASHING

The principles of extrusion cooking are summarised. In small scale trials good extracts were obtained from extruded barley when it was mashed with industrial enzymes, using a programmed temperature cycle. Extruded barley, wheat and maize and wheat flour yielded acceptable levels of extract when mashed with lager malt (70%) using a programme with 1 hour rests at 50°C and 65°C. The extracts obtained from these grists were increased above those obtained from grists of lager malt alone and the viscosities of the worts were reduced when the mashes were supplemented by preparations of bacterial enzymes. Enzyme additions also improved extract recoveries from all-malt mashes and reduced the viscosities of the derived worts. Using a temperature programmed mashing cycle and supplementary enzymes beers were prepared from a lager malt grist and grists in which the lager malt was partly replaced, by 30%, with extruded barley or extruded wheat, or extruded maize or wheat flour pellets. In every case wort was recovered relatively easily, the worts fermented normally and the beers were all fully acceptable, although their flavours did differ. However, in contrast to results of preliminary brewing trials, the head retentions of the beers made with adjuncts were unusually low, possibly because of particular enzyme additions.     

Quality characteristics of triticale malts and worts

Worts from triticale malts, in particular well modified malts, separated poorly from mashes. Worts prepared at 70° C had high viscosities (10–27 cSt) indicating that problems would occur during filtration in brewing. The viscosities of triticale worts were higher than those of worts from barley malts. In addition, worts from well modified malts were generally turbid. Proteinaceous material (partly degraded prolamins) was the primary cause of this turbidity. Although the degree of malt modification did influence the rate of wort separation, it had little effect on wort viscosity. High viscosity was caused by pentosans dissolved from the triticale malt during mashing. Oxidative gelation was not observed with these pentosans. Grains and malts were fractionated, and the high molecular weight fractions were analysed for their sugar and acyl components. All were rich in arabinose and xylose. There was a rough inverse correlation between the solubility of the poly saccharide fractions and the levels of substitution with acetyl and feruloyl residues. The poor wort separation from triticale malt grists appeared to be related to the particle size distributions, which were narrow. The sedimentation values of the grist ‘fines’ were high.     

STARCH HYDROLYSIS IN MALTING AND MASHING

Starch hydrolysis in malting and mashing processes was studied by gel chromatography on Sepharose Cl 4B. The final molecular weight distribution of starch components in malt differs from those in barley. During malting a molecular weight fraction close to the void volume appears as an intermediate product. Minor differences in starch hydrolysis in mashes with different malts is obtained, though the final dextrin composition of the worts is similar.     

The development of rancidity in husked and naked oats after storage under various conditions

The levels of hydrolytic and oxidative rancidity have been estimated in husked and naked (huskless) oat varieties stored under different conditions, viz. (i) varying moisture content, (ii) varying oxygen availability, (iii) after bruising, and (iv) after drying at different temperatures. Hydrolytic rancidity increased at higher moisture contents and with storage period but generally the level in naked oats only exceeded that of husked oats if the grain was severely bruised. No oxidative rancidity was detected in husked or naked oats under any of the treatments used.     

Malted and unmalted oats in brewing

Using oats as a raw material in brewing has recently become the focus of increased interest. This is due to research findings that have shown that oats can be consumed safely by coeliac sufferers. It is also a response to consumer demand for products with novel sensory properties. In this study, beer was produced entirely from oat malt, from barley malt and from oat and barley malts mixed with various quantities of unmalted oats. Compared with barley wort, wort made from malted oats provided a lower extract content and had a higher protein content, but a lower free amino nitrogen content (FAN). The oat wort also showed increased viscosity and haze. The addition of unmalted oats during wort production produced significant changes in the physico‐chemical parameters of both oat and barley worts and beers. Unmalted oats caused an increase in wort viscosity and haze, and a reduction in total soluble nitrogen and FAN. Unmalted oats also contributed to lowering the concentration of higher alcohols and esters. Beer made from 100% oat and barley malts exhibited a similar alcohol content. The use of an oat adjunct in both cases resulted in a lower ethanol content. The introduction of enzyme preparations during the production of wort with oat adjunct had many benefits: increased extract content and FAN; a higher volume of wort; and a lower viscosity that led to faster wort filtration. This research suggests that the use of enzymes is necessary to make production using a high proportion of oats in the grist profitable. Copyright © 2014 The Institute of Brewing & Distilling     

Effects of cultivar,nitrogen fertilization rate and environment on yield and grain quality of barley

Ten barley cultivars, including covered and naked types, varying in their content of total starch, amylose, protein and β-glucan, were grown in different years, at various locations and nitrogen fertilization rates. The barley cultivars showed a large variation in yield (3250–6690 kg ha⁻¹), thousand kernel weight (40–50 g), bulk weight (660–815 g litre⁻¹), starch (51–67% of DM), protein (8–15% of DM), β-glucan (3·5–5·9% of DM) and ash (1·9–2·5% of DM). The naked cultivar SW 8775 had the highest starch content and the high amylopectin cultivar (SW 7142-92, waxy) had the lowest. The waxy starch barleys had the highest protein content, while the normal starch barleys (Golf and Lina) had the lowest protein content at each N-rate. Higher content of β-glucan was found in the waxy cultivars (5·0–5·9% of DM) and high amylose cultivars (5·6–5·9% of DM) than in the other barley cultivars (3·5–4·8% of DM). The results were evaluated by analysis of variance (ANOVA) and principal component analysis (PCA), and both confirmed that nitrogen fertilization rate was of great importance for the protein content. PCA revealed that protein and β-glucan were negatively correlated with starch and yield. The ANOVA showed that the cultivar factor was significant for all variables, but especially for the β-glucan content, which responded differently to the nitrogen fertilization rate during the 2 years. In this study, environmental effects were generally of less importance than the barley cultivars for the different variables. © 1998 Society of Chemical Industry.     

裸燕麦米和燕麦粉加工所得麸皮中β-葡聚糖和酚酸的分布

选取具有代表性的裸燕麦品种,分析燕麦麸皮和胚乳所占的比例和微观结构特征;同时分析β-葡聚糖和酚酸在燕麦麸皮（果皮、种皮＋糊粉层）和胚乳中的分布,并验证了现有燕麦米和燕麦粉主流加工方式的适宜程度。结果表明,在所选裸燕麦品种中,β-葡聚糖均富集在麸皮中,质量分数达8.57%,约是胚乳中含量的4.5?倍;麸皮中p-香豆酸和阿魏酸的含量分别达0.099?mg/g和1.00?mg/g,分别是胚乳中相应含量的24?倍和48?倍;在麸皮中,果皮中p-香豆酸和阿魏酸含量分别约为种皮＋糊粉层中的13?倍和2.7?倍。研磨制燕麦米所得第2道麸皮中,β-葡聚糖质量分数平均为1.7%,远小于麸皮中的平均含量,加工程度适宜;而燕麦制粉所得第4道和第5道麸皮,β-葡聚糖质量分数达6.73%和7.80%,接近糊粉层中β-葡聚糖含量,加工过度。综上可知,利用分析燕麦加工所得麸皮中葡聚糖和酚酸含量,可初步判定燕麦米和燕麦粉的加工程度,为其加工提供技术支撑。     

SMALL SCALE MASHING EXPERIMENTS WITH GRISTS CONTAINING HIGH PROPORTIONS OF RAW SORGHUM

Small scale mashes (50 g total grist) with grists containing high proportions of raw sorghum (50%–80% malt replacement) showed high values of extract recovery and produced worts of lower total nitrogen, free amino nitrogen, viscosity and colour but higher values of pH compared to worts produced from all malt mashes. Increasing the proportion of raw sorghum in the grist relative to malt resulted in a decline in extract recovery, wort total nitrogen, free amino nitrogen and an increase in wort pH. Addition of industrial enzyme preparations to mashes containing raw sorghum resulted in higher values of extract recovery (enzyme preparations containing α amylase and β glucanase), higher values of wort total nitrogen and free amino nitrogen (enzyme preparations containing a neutral proteinase) and decreased wort viscosity (enzyme preparations containing β glucanase or cellulases) compared to worts produced from untreated mashes. Worts and beers were produced on a pilot brewery scale from 50% malt and 50% polished (whole) sorghum (single decoction mashing regime) and 20% malt and 80% raw sorghum supplemented with an industrial enzyme preparation (double mashing regime). Mashes comprising 50% malt and 50% polished sorghum showed comparable wort filtration behaviour (lautering) to that of control mashes (70% malt and 30% maize grists) whereas wort produced from 20% malt and 80% raw sorghum filtered slowly. Worts produced from grists containing sorghum were of high fermentability and showed lower levels of total nitrogen and free amino nitrogen compared to control worts. Analysis of worts produced from small scale mashes containing raw sorghum and a pilot brewery scale mash comprising 20% malt and 80% raw sorghum demonstrated that the levels of total nitrogen and free amino nitrogen were higher than expected from the reduction in the malt content of the mash, consistent with the release of nitrogenous components (polypeptides, peptides and amino acids) derived from sorghum into the wort. Beers produced from 50% malt and 50% polished sorghum and 20% malt and 80% raw sorghum were filtered without difficulty and were of sound flavour. Beers produced from 50% malt and 50% polished sorghum contained lower levels of isobutanol, 2-methylbutanol, dimethylsulphide and higher levels of n propanol and diacetyl compared to control beers.