THE PROPERTIES,COMPOSITION AND FERMENTABILITIES OF WORTS MADE FROM 100% RAW SORGHUM AND COMMERCIAL ENZYMES

A mashing regime was developed using 100% raw sorghum which enabled commercially acceptable hot water extracts to be obtained in 85 minutes with minimal use of a heat stable α-amylase and proteolytic enzymes. This gave worts of HWE 295 1°/kg, with FAN levels of about 40 mg/l and ammonium ion concentration of about 60 mg/l. Higher, but commercially unacceptable, levels of proteolytic enzymes gave worts with FAN from 84.5 to 95 (mg/l). Addition of an amyloglucosidase as the commercial preparation Amylo300L, was required to convert the HWE to fermentable extract. The addition of Amylo300L, increased the DP1, DP2 and DP3 carbohydrate fractions of the worts from 22% to more than 90% of the total, compared to about 80% for a wort made from malted barley without the use of enzymes. Two different proteolytic enzymes gave different extracts and FAN contents presumably reflecting either differences in susceptibilities of the sorghum to the two enzymes or the presence of different additional enzyme activities in the different preparations. The level of ammonium ions in malted barley worts was 86 mg/l and up to 88 mg/l in worts produced from sorghum and enzymes. Enzyme addition produced increased levels of ammonia. The content of Group A (the most readily assimilated) amino acids was proportionally higher in sorghum worts compared to malted barley wort. Worts made from raw sorghum and enzymes, containing as little as 40 mg/l FAN, were fully attenuated. The yeast consumed about 35 mg/l FAN and 45 mg/l ammonium ions. Under identical fermentation conditions, the same yeast, fermenting a malted barley wort of comparable extract consumed 104 mg/l FAN and 37 mg/l ammonium ions.     

FERMENTATION OF WORTS MADE FROM 100% RAW SORGHUM AND ENZYMES

Worts made from raw sorghum and enzymes were successfully fermented even though the level of FAN present (51 mg/l) is well below that essential for fermentation of wort made from malted barley. Changes in typical fermentation parameters such as specific gravity, pH uptake of free amino nitrogen (FAN) and ammonium ions mirrored the increase in yeast cell concentration. Yeast viability remained high throughout the fermentation. Under identical fermentation conditions, malted barley worts showed typical fermentation profiles. However, malted barley worts with specific gravity maintained by the addition of D-glucose, but in which the FAN was diluted to a level similar to that found in a wort made from sorghum and enzymes, fermented more slowly and failed to attenuate fully. Five consecutive fermentations, using yeast cropped from the preceding to pitch the current fermentation were conducted. The specific gravity profiles were essentially the same in all five fermentations. Final values of pH, yeast in suspension, yeast viability and FAN were also indistinguishable. The yeast crop taken from fermentations of worts made from raw sorghum and enzymes represented a 5-fold increase over the initial pitching rate. When compared to commercial beers, the beers derived from fermentation of worts made from raw sorghum and enzymes contained lower levels of ethyl acetate, and higher levels of both 2- and 3-methyl butanol. In the beers derived from sorghum, isobutanol was always less than 20% of the total higher alcohol concentration.     

ROLE OF ALPHA-GLUCOSIDASE IN THE FERMENTABLE SUGAR COMPOSITION OF SORGHUM MALT MASHES*

The cause of the high glucose to maltose ratio in sorghum malt worts was studied. Mashing temperature and pH strongly affected both the amount of glucose and the proportion of glucose relative to total fermentable sugars. The relative proportion of glucose was higher when mashing was performed. at pH 4.0, close to the pH optimum for sorghum alpha-glucosidase, than at the natural pH of the mash (pH 6.0–5.5). Mashing according to the EBC procedure using an enzymic malt extract with pre-cooked malt insoluble solids producing a wort containing maltose and glucose in an approximately 4:1 ratio, whereas mashing with a malt extract without pre-cooking the malt insoluble solids resulted in a wort with approximately equal amounts of maltose and glucose. Both treatments gave the same quantity of total fermentable sugars and amount of wort extract. Sorghum alpha-glucosidase was confirmed to be highly insoluble in water. All or virtually all activity was associated with the insoluble solids. Hence, it appears that the high amount of glucose formed when sorghum malt is mashed conventionally is due to alpha-glucosidase activity. Pre-cooking the malt insoluble solids inactivates the alpha-glucosidase, preventing the hydrolysis of maltose to glucose.     

EXTRACTION AND ASSAY OF PROTEOLYTIC ACTIVITIES IN SORGHUM MALT

A method has been developed to assay the proteinase and carboxypeptidase activities in sorghum malt. The method specifically addresses two problems encountered with some other assays for malt proteolytic activity; that of enzyme inextractability and the use of alien substrates. It was found that as with barley malt proteolytic enzymes, a high proportion of sorghum malt proteolytic activity was inextractable with sodium chloride solution. Systematic investigation into the extraction of proteolytic enzymes from sorghum malt led to the development of a novel extractant viz. 0.6 M Lithium iodide LiI plus 3.33 mM dithiothreitol. This extractant appears to solubilize a significantly higher proportion of the malt proteolytic activities with a single extraction than previously used buffers. Assay is carried out Using purified Kafirin, the sorghum prolamin storage protein, as substrate. Proteinase is measured in terms of total nitrogen solubilized and carboxypeptidase as free α-amino nitrogen solubilized.     

COMPARISON OF THE MALT CHARACTERISTICS OF TRADITIONAL AND IMPROVED VARIETIES OF SORGHUM VULGARE FROM GHANA

The malt characteristics of six agronomically improved varieties of sorghum in Ghana were compared to traditionally grown local varieties. The diastatic activities of the traditional varieties were found to be better than the improved breeds. The Improved breed, Kadaga, produced extract yields comparable to the traditional varieties. Free amino nitrogen content of Nagawhite worts were also comparable to those of the traditional varieties. The malt characteristics of all the varieties tested varied remarkably, but none of the improved breeds was found to be better than the traditional varieties in terms of their potential in brewing.     

EFFECT OF ALKALINE STEEPING ON WATER UPTAKE AND MALT QUALITY IN SORGHUM

Condensed tannin-free and high-tannin sorghum grain were steeped in dilute alkali and the effects on water uptake during steeping and final malt quality were determined. With the condensed tannin-free sorghum, steeping in dilute alkali led to increased water uptake during steeping and an improvement in malt quality in terms of diastatic power and free amino nitrogen. These effects are presumed to be due to the alkali opening up the pericarp cell wall structure of the grain, allowing more rapid water uptake. Best results were obtained by application of alkali early in steeping, presumably because the grain is less susceptible to alkali toxicity than later in steeping. Steeping high-tannin sorghum in dilute alkali did not improve malt quality. This appeared to be because water uptake was not increased to the same extent as with condensed tannin-free sorghum, as the alkali reacted with the tannins .     

AN APPROACH TO THE ESTIMATION OF BREWING QUALITY IN BARLEY AND MALT

Methods of assessing the brewing qualities of new varieties are reviewed. A new method for making this assessment is proposed. This is ideally a three-step process but it would be possible to eliminate the third, costly, step without severe loss of effectiveness. The use of the new method is illustrated by reference to trials using 251 samples from recent trials in France.     

DETERMINATION OF REPEATABILITY AND REPRODUCIBILITY OF A NEW RAPID ENZYME METHOD FOR THE DETERMINATION OF GLYCOSIDE NITRILE IN MALTED BARLEY

A new rapid method for the determination of malt glycosidic nitrile, using an enzymatic incubation with beta-glucosidase, was tested in an inter-laboratory collaborative trial. Repeatability (r₉₅) and reproducibility (R₉₅) values are reported. A limited comparison is made with the existing determination of malt combined nitrile using methods involving laboratory fermentations.     

A RAPID AND SIMPLE METHOD FOR THE DETERMINATION OF STARCH AND β-GLUCAN IN BARLEY AND MALT

A simple and precise method suitable for the routine determination of starch and β-glucan in barley and malt is described. Perchloric acid (50 mM) was used to effect rapid (3 min) and exhaustive extraction of both glucans which were then measured directly from this single extract by specific enzymic hydrolysis of the individual glucans to glucose. The glucose was also measured enzymically. Little or no acid hydrolysis of starch or β-glucan was observed under the extraction conditions used; most or all of the free glucose could be attributed to hydrolysis of sucrose. Complete solubilisation of the gum and hemicellulosic components of β-glucan was achieved. Preincubation of the acid extracts with protease prior to amyloglucosidase digestion resulted in higher measurements (approximately 4% w/w) of starch. The method was used to measure the levels of starch and β-glucan in five varieties of barley with contrasting malting quality, in micro-malts prepared from these samples and in commercial lager and ale malts.     

DURATION OF FINAL WARM STEEP AS A CRUCIAL FACTOR IN PROTEIN MODIFICATION IN SORGHUM MALTS

Cold water soluble protein (CWS-protein), cold water soluble protein modification index, total non-protein nitrogen (TNPN), small peptide accumulation, free alpha amino nitrogen, carboxy-peptidase and proteinase activities, all protein modification indicators in malts from two improved Nigerian sorghum cultivars were estimated after six days of malting. Grains were steeped in distilled water for a total of 48 h under four different final warm steep (40°C) treatment periods. Cultivar and duration of final warm water steep, plus their pair-wise interactions highly significantly influenced all these protein modification indices. Sorghum ICSV 400 generally exhibited higher FAN, CWS-protein solubilising activity and accumulation, superior amylolytic potential over proteolysis and better protein modification potential over KSV 8. Lower TNPN and TNPN-FAN difference exhibited by ICSV 400 in spite of its higher FAN suggests superior anabolic protein turnover probably due to more efficient peptide translocation process. Proteolytic activities recorded for both cultivars were inconsistent with levels of N-substances obtained suggesting roles for factors other than proteolysis in grain protein modification.     

DETERMINATION OF THE MOISTURE AND NITROGEN CONTENTS OF BARLEY AND MALT BY NEAR INFRARED SPECTROSCOPY (NIRS)

The determination of the moisture and nitrogen contents of barley and malt by near infrared spectroscopy (NIRS) has been tested by the Analysis Committee of the European Brewery Convention. In the collaborative trial four samples of barley and malt were analysed by 17 laboratories. Repeatability (r₉₅) and reproducibility (R₉₅) values of 0.3 and 1.5% m/m respectively were obtained for barley moisture over the range 12.7 to 15.8% m/m. For malt moisture these values were 0.2 and 1.3% m/m over the range 4.0 to 4.3% m/m, for barley nitrogen 0.1 and 0.3% m/m on dry matter over the range 1.57 to 2.14% m/m, and for malt nitrogen 0.1 and 0.2% m/m on dry matter over the range 1.58 to 1.82% m/m, respectively.     

THE MILLING ENERGY OF MALTED BARLEY AND ITS RELATIONSHIP WITH HOT WATER EXTRACT AND α-AMYLASE ACTIVITY

Hot water extract is dependant on endosperm structure and its breakdown during malting. These endosperm characteristics can be rapidly assessed on 5 g samples by measuring the milling energy of malted barley. α-amylase determinations on the resultant flour indicate that good malting barleys have either moderate or high levels of the enzyme. High levels of α-amylase will not confer good malting quality where endosperm modification has proceeded slowly.     

USE OF TITANIUM DIOXIDE AS A CATALYST IN THE KJELDAHL DETERMINATION OF THE TOTAL NITROGEN CONTENT OF BARLEY,MALT AND BEER

Titanium dioxide can be used to replace selenium in the Kjeldahl determination of total nitrogen without sacrifice of precision; higher temperatures for digestion are required than when selenium is the catalyst.     

DIFFERENT RATES OF DEVELOPMENT OF α-AMYLASE IN DISTAL ENDOSPERM ENDS OF GERMINATED (MALTED) CHARIOT AND TIPPER BARLEY VARIETIES

Chariot Barley had a faster malting rate than Tipper. Even when the total levels of the aleurone-produced enzyme α-amylase were similar in both Chariot and Tipper, the distal ends of the grains of Chariot developed α-amylase at a faster rate than the corresponding endosperm ends of Tipper. The excised aleurone layers of Chariot and Tipper had similar potentials to produce α-amylase. Therefore the faster rate of development of α-amylase in the distal ends of the grains of Chariot may reflect faster transport of active gibberellic acid through the aleurone layer. Differences in the rates of transport of gibberellic acid through the plasmodesmata of the aleurone layer may determine the efficiency of production and distribution of endosperm-degrading enzymes during malting. The transport of gibberellic acid in the aleurone layer was facilitated by high moisture levels.     

THE BREWING POTENTIAL OF “ACHA” (DIGITARIA EXILIS) MALT COMPARED WITH PEARL MILLET (PENNISETUM TYPHOIDES) MALTS AND SORGHUM (SORGHUM BICOLOR) MALTS

The malting and brewing characteristics of millets (Pennisetum typhoides and Digitaria exilis) and sorghum (Sorghum bicolor) were compared. Diastase, α-amylase, amyloglucosidase and proteases increased with malting time and the increase was associated with the modification. Development of hydrolytic enzymes was significantly higher in pearl millet and Digitaria exilis (“acha”) than in sorghum at P ≥ 0.01. The major starch degrading enzyme in the three varieties of pearl millet (SE composite, SE.13 and SE 2124) was α-amylase. On the other hand, β-amylase was the major starch degrading enzyme in “acha” (Digitaria exilis) which is similar to the pattern in barley. Gibberellic acid had a stimulating effect on the diastatic activity of pearl millets, Digitaria exilis (“acha”) and sorghum (KSV-4), but inhibited the diastatic activities of sorghum (Farafara). Gibbereltic acid inhibited the proteolytic activities in all the pearl millet varieties, Digitaria exilis and sorghum varieties. Potassium bromate had little or no effect in the reduction of malting losses. Although “acha” (Digitaria exilis) had a high β-amylase content, a high malting loss makes it uneconomical to brew with “acha” mart. A blend of “acha” malt with pearl millet malt or sorghum malt (composite malt) will produce a malt of the same profile as barley malt and this will enhance the quality of sorghum and pearl millet malt during the mashing process. Wort quality of all the samples was suitable for brewing conventional beer.