Showing papers in "Journal of The Institute of Brewing in 1974"
TL;DR: In this paper, the authors studied the effects of fermenting wort of unusually high specific gravity, followed by dilution with water to give beer of normal original gravity, but matching of flavors requires control of the level of flavour determinants.
Abstract: Some effects have been studied of fermenting wort of unusually high specific gravity, followed by dilution with water to give beer of normal original gravity. This procedure permits increased overall rates of beer production, but matching of flavours requires control of the level of flavour determinants. If not controlled, the concentration of volatile esters may be disproportionately increased so that, after dilution, beer flavour is markedly different. Higher alcohol production is not affected in this way. The concentration of esters can be adjusted to appropriate levels by increasing the production of yeast mass during fermentation. Unsaturated fatty acids, which increase yeast dry matter production without altering the rate of fermentation, are particularly effective in reducing the extent of ester synthesis.
73 citations
TL;DR: The β-glucan from ungerminated barley with water at 40 °C has a much lower specific viscosity than the corresponding material isolated from a wort prepared at 65 °C from a two-day germinated malted barley malt as mentioned in this paper.
Abstract: The β-glucan extracted from ungerminated barley with water at 40 °C has a much lower specific viscosity than the corresponding material isolated from a wort prepared at 65 °C from a two-day germinated barley malt. Both glucans are similar in that they are polymers of β-D-glucose, with approximately 74% of the linkages in the β-1,4 configuration and 26% in the β-1,3 configuration. However, the two glucans are not hydrolysed to the same extent either by a partially purified bacterial endo-β-1,3-glucanase or by a homogeneous endo-β-1,3-glucanase from malted barley. The malt glucan is readily hydrolysed, causing a rapid decrease in specific viscosity but with no measurable increase in reducing power, whereas barley glucan undergoes only limited hydrolysis under similar conditions. Thus, different β-glucan preparations from barley or malt may be identical in the proportion of β-1,3 to β-1,4-linkages but the overall arrangement of linkages, and hence susceptibility to enzyme attack, differs according to the source and the method of extraction of the glucan. The molecular weights of both β-glucan preparations and the products of their enzyme hydrolysis have been determined by agarose gel permeation chromatography. A simple model which illustrates the underlying structural relationships of the β-glucans from barley and malt is suggested.
68 citations
TL;DR: The role of oxygen in yeast metabolism in brewery fermentation is surveyed and variations in oxygen availability, by modifying yeast activity, can affect beer flavour.
Abstract: In suitable circumstances, yeast activity during brewery fermentation may be controlled by regulation of the supply of oxygen. Yeasts can be divided into four classes depending on their susceptibility to such control. Propagation methods and wort composition influence the magnitude of the requirements for oxygen. Variation in oxygen availability, by modifying yeast activity, can affect beer flavour. The role of oxygen in yeast metabolism in brewery fermentation is surveyed.
66 citations
TL;DR: In this article, the results of viscosity measurements of suchextracts are compared with published information on l-glucan contents and with maltsters' assessmentsofanumber of barleyvarieties.
Abstract: Asimpletechniquefordeterminingtheviscosityofextractsofsmallsamplesofbarleygrainsis requiredforusein screeninglargenumbersofselectionsin abreeding programme. Extraction of 2-g samples of ground grain at pH 1-5has proved satisfactory and the results of viscosity measurements of suchextracts are compared with published information on l-glucan contents andwithmaltsters'assessmentsofanumberofbarleyvarieties.Keywords: barley, gum, method, selection,
60 citations
TL;DR: The acid content of a range of ales and lagers has been measured for some organic acids related to the Krebs cycle, and found to vary widely, suggesting that yeast converts pyruvate to acetate towards the end of fermentation.
Abstract: The acid content of a range of ales and lagers has been measured for some organic acids related to the Krebs cycle, and found to vary widely. Acetate, pyruvate, lactate, succinate, pyroglutamate, malate and citrate were present in all cases and α-ketoglutarate was usually detected. α-Hydroxyglutarate was recognized in a number of beers. The effect of the acids on the pH of beer is assessed. The strain of yeast which is used markedly influences the levels of all acids except pyroglutamate and the conditions of yeast propagation have a substantial influence on the extent of acid accumulation. During the fermentation of wort and synthetic media the extent of organic acid excretion is proportional to the extent of fermentation, but the nature of the acids which are excreted varies during the fermentation period. In synthetic media, nitrogen source is shown to have a substantial effect on the accumulation of organic acid. Pyruvate and acetate levels vary inversely towards the end of fermentation, suggesting that yeast converts pyruvate to acetate.
57 citations
TL;DR: The present knowledge of the biochemistry of cider components and the effect of environmental factors, together with information which can be drawn from other fields, encourages the belief that cider flavour could be controlled to a much greater degree than it is at present.
Abstract: The use of sulphur dioxide, inoculating with known yeasts and fermenting to dryness has solved many of the problems of the early cider industry leaving present day cider research to investigate the control of the final cider flavour. Before this can be accomplished it is essential to have detailed knowledge of the volatile and non-volatile constituents of cider, the contribution these components make to the flavour, the bio-synthetic pathways by which they are formed and the factors which affect the amounts produced. Research has already provided much analytical information and the use of threshold values enables useful data to be obtained on their flavour contribution. The approach of correlating taste panel data obtained on the cider in its entirety with the analytical data offers a means of supplementing this informaion.
Our present knowledge of the biochemistry of cider components and the effect of environmental factors, together with information which can be drawn from other fields, encourages the belief that cider flavour could be controlled to a much greater degree than it is at present.
52 citations
TL;DR: A flame-photometric sulphur detector was used to identify, measure and determine the sources of the sulphur volatiles produced during the commercial processing of British ale and lager.
Abstract: A flame-photometric sulphur detector was used to identify, measure and determine the sources of the sulphur volatiles produced during the commercial processing of British ale and lager. Dimethyl sulphide was the main sulphur volatile present in malt but traces of hydrogen sulphide, diethyl sulphide, and dimethyl disulphide were also detected. Hops contained hydrogen sulphide, methyl mercaptan, dimethyl sulphide, diethyl sulphide, methional and dimethyl disulphide. Most of this material extracted into commercial worts was driven off during boiling. Brewing yeasts produced only traces of organo-sulphur volatiles both in laboratory fermentations of wort and during the processing of commercial ales and lagers. In contrast, brewery bacteria, particularly wort spoilage organisms, could generate dimethyl sulphide and sometimes traces of other sulphur volatiles in laboratory cultures. t-Butyl mercaptan was the only organo-sulphur volatile detected in significant concentrations during the primary fermentation and conditioning of commercial beers and this was attributable to the activity of wort-spoilage bacteria. Attempts to identify a volatile compound causing ‘sulphury’ smells in beer were unsuccessful but there was some evidence that it might not contain sulphur.
46 citations
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TL;DR: The dextrins in beer exhibit a characteristic wavy distribution with respect to their molecular weight, so that these dextrin seem to fall into distinct groups. as discussed by the authors showed that the majority of the α-1,6 linkages in amylopectin survive the brewing process.
Abstract: The dextrins in beer exhibit a characteristic wavy distribution with respect to their molecular weight, so that these dextrins seem to fall into distinct groups. These groups of dextrins (I, II, III and IV corresponding to DP 5–10, DP 11–16, DP 17–21 and DP 22–27) have been isolated by gel-chromatography on Bio-Gel P-2. Debranching of the megalosaccharides in Groups II, III and IV by means of pullulanase shows that they contain two, three and four α-1,6 linkages respectively. The dextrins in Group I are either linear or singly-branched. The distribution patterns of the constituent, linear maltosaccharides have been determined and some likely structures for the multiply-branched dextrins are suggested. The results indicate that the majority of the α-1,6 linkages in amylopectin survive the brewing process; 25% of the α-1,6 linkages show up as singly-branched oligosaccharides and at least 35% as multiply-branched megalosaccharides of DP 11–30. With respect to the fine structure of amylopectin, the implication is that although the average interior chain length is about 6 glucose units, at least 35% of the α-1,6 linkages occur in densely branched clusters (pairs, triplets, quadruplets, etc.), the interior chain length of which is about 3 glucose units. This in turn offers an explanation of the wavy distribution of the dextrins in wort and beer.
45 citations
TL;DR: Beer flavour with respect to fusel alcohols and esters, volatile sulphur compounds, carbonyl compounds and volatile phenols is seriously influenced by wort enterobacteria.
Abstract: Of the family Enterobacteriaceae, Citrobacter freundii, Enterobacter aerogenes, Ent. cloacae, Hafnia alvei, Klebsiella aerogenes and Serratia species have been detected in fermenting wort. Escherichia coli and animal parasites have not been isolated. As shown by G.C. ratio, DNA base sequence comparison, numerical taxonomy and phage typing, Obesumbacterium proteus shares the same family and is placed in the genus Hafnia as H. protea, with two subspecies. H. protea survives brewery fermentations better than other members of the family and is therefore common in pitching yeast. However, all wort enterobacteria are sensitive to pH values below 4.4 and to a lesser degree to ethanol concentrations over 2% (w/v). Rates of brewery fermentations may be retarded by enterobacteria and the beer pH elevated. Other wort bacteria isolated, species of Achromobacter, Acinetobacter and Pseudomonas, are sensitive to pH and ethanol, and present in smaller numbers in wort than the enterobacteria. Beer flavour with respect to fusel alcohols and esters, volatile sulphur compounds, carbonyl compounds and volatile phenols is seriously influenced by wort enterobacteria. Isolation and enumeration of the enterobacteria in fermenting wort are conveniently carried out on MacConkey agar medium; H. protea colonies grow in 48–72 h at 30°C but the other enterobacteria produce colonies in 20–30 h.
43 citations
TL;DR: Commercial application of gibberellic acid during malting supplements the natural endogenous levels of this hormone, which accelerate the production and release into the endosperm of enzymes which degrade the hemicellulosic-protein-starch complex into essential brewing materials such as sugar, peptides and amino acids.
Abstract: Over the last 15 years numerous studies, both fundamental and applied, have ensured for gibberellic acid (GA3) a firm place in the routine commercial malting of barley and the production of fruits. A large number of the thirty-eight gibberellins so far characterized occur naturally, e.g. gibberellic acid in germinating barley. Commercial application of gibberellic acid during malting therefore supplements the natural endogenous levels of this hormone. Small additions of gibberellic acid accelerate the production and release into the endosperm of enzymes which degrade the hemicellulosic-protein-starch complex into essential brewing materials such as sugar, peptides and amino acids.
A combination of abrasion with gibberellic acid application results in further acceleration of the malting process. Abrasion of the pericarp at the distal end of barley grains allows them, in the presence of normal levels of gibberellic acid, to malt simultaneously from both their embryo and non-embryo ends: malting time is drastically reduced and soluble malt extract is increased.
In spite of the widespread industrial use of gibberellic acid, the cellular mechanisms through which gibberellic acid elicits its various actions on plant growth and development are not yet known; however, with barley aleurone cells gibberellic acid can induce drastic reorganization and synthesis of subcellular organelles. The net result of gibberellin treatment may be vigorous production and secretion of hydrolytic enzymes or, in other circumstances a rapid acceleration of growth and development. It is as yet unknown whether these apparently diverse expressions of gibberellin action have a similar biochemical basis.
43 citations
TL;DR: In this paper, a dimer of catechin has been separated from a number of ales, stouts and lagers and has been shown to have the same structure as procyanidin B3, which has previously been isolated from plant sources.
Abstract: A dimer of catechin has been separated from a number of ales, stouts and lagers. This compound has been shown to have the same structure as procyanidin B3, which has previously been isolated from plant sources. It can be conveniently synthesized from dihydroquercetin and catechin.
TL;DR: In this article, the most complex types of nitrogen compound in beer (here termed "proteoses") are, when not combined with polyphenols, highly surface active and hence concentrate in the foam.
Abstract: The most complex types of nitrogen compound in beer (here termed “proteoses”) are, when not combined with polyphenols, highly surface active and hence concentrate in the foam. With unhopped beer, the foam is of the “liquid-viscous” type, which eventually drains and collapses leaving no residual solids. The iso-α-acids in hopped beers are also surface-active, so they too are concentrated in the foam. At the corresponding concentration in bulk solution the solubility limits of some isohumulates* are exceeded. Thus we believe that solids are similarly formed in the bubble films, so that these are reinforced and stiffened to give “cling”. One consequence of the increased concentration of iso-α-acids in the foam is that there can be precipitation of iron, nickel, cobalt and zinc isohumulates. This results in concentration of these metals in foam.
The most significant finding is that the concentration of both proteoses and iso-α-acids in the foam exceeds the bulk solubility limits and results in the formation of proteose-isohumulate salts which make the main contribution to the solid reinforcement of bubble films.
These findings make it possible to explain satisfactorily “lacing” or “cling” and also isohumulone losses (a) during boiling and trub separation, (b) during post-fermentation bittering, and (c) during any subsequent foam formation. An explanation is also provided why losses of bitterness and of head retention are linked. Consequently, linked recovery of both bitterness and head retention can occur, as has been found is some recent fermentation improvements, such as continuous fermentation.
TL;DR: In a Norwegian all-malt pilsener beer organoleptic threshold values were determined for the following acids: acetic, propionic, n-butyric, isobutyric and n-valeric as discussed by the authors.
Abstract: In a Norwegian all-malt pilsener beer organoleptic threshold values were determined for the following acids: acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, caproic, caprylic, pelargonic, capric, undecanoic, lauric, citric, lactic, tartaric, malic, malonic and succinic.
TL;DR: In this paper, an ammonia probe was used to replace the distillation-titration procedure for estimating the ammonium content of Kjeldahl digest solutions, which gave results of comparable accuracy and precision.
Abstract: An ammonia probe has been used to replace the distillation-titration procedure for estimating the ammonium content of Kjeldahl digest solutions. A procedure is described for estimating the total nitrogen content of barley, malt, wort and beer. The semi-micro digestion stage is performed as a batch procedure and the ammonium content of the acid digest estimated automatically in a continuous flow system at a rate of 60 samples per hour. The method is more rapid than the classical distillation-titration procedure and gives results of comparable accuracy and precision.
TL;DR: The effect of the addition of a range of monomeric, dimeric and polymeric polyphenols to beer on the rate of haze formation has been examined in this paper.
Abstract: The effect of the addition of a range of monomeric, dimeric and polymeric polyphenols to beer on the rate of haze formation has been examined. Monomeric polyphenols had no significant effect on haze formation. The addition to beer of dimeric or polymeric polyphenols caused a large increase in the rate of haze formation.
TL;DR: In this article, the authors used a high gravity brewing system in which worts of 1080° gravity were fermented and the resulting beers diluted to give an O.G. of 1040°.
Abstract: Pilot brewing trials have shown that beers of good flavour can be produced using a high gravity brewing system in which worts of 1080° gravity are fermented and the resulting beers diluted to give an O.G. of 1040°. The flavour can differ from that of the control beers in that the diluted beers retain more ester and strong ale character. Trials have been carried out to study possible methods for control of ester production to permit product matching. A promising approach is controlled contact with oxygen during fermentation.
TL;DR: Crossed immunoelectrophoresis was used to estimate four aminopeptidases in organs of germinating barley, and to demonstrate non-identity, identity and partial identity between barley and malt proteins.
Abstract: Quantitative immunoelectrophoresis techniques were applied to the study of barley and malt proteins. By crossed immunoelectrophoresis of malt more than 54 immunochemically distinct proteins were distinguished, whereas only 24 proteins have been included in the E.B.C. system of reference based on electro-immunodiffusion.* Crossed immunoelectrophoresis was also used to estimate four aminopeptidases in organs of germinating barley, and to demonstrate non-identity, identity and partial identity between barley and malt proteins. Tandem crossed immunoelectrophoresis was used to compare the proteins in extracts of barley and malt and rocket immunoelectrophoresis to determine an α-amylase in germinating barley. Fused rocket immunoelectrophoresis was used to detect elution patterns of individual barley proteins after ion exchange chromatography, and line immunoelectrophoresis to compare three barley antisera. Advantages of quantitative immunoelectrophoresis over electro-immunodiffusion are demonstrated and discussed. A new system of reference for barley and malt proteins based on crossed immunoelectrophoresis is suggested.
TL;DR: A β-amylase polymorphism (electrophoretic forms Sd1 and Sd2) in barley malt is shown to be closely associated with the proportion of free to total (free plus latent) β-Amylase, but not with the level of total β- amylase in the mature grains of 46 cultivars.
Abstract: A β-amylase polymorphism (electrophoretic forms Sd1 and Sd2) in barley malt is shown to be closely associated with the proportion of free to total (free plus latent) β-amylase, but not with the level of total β-amylase in the mature grains of 46 cultivars. All of the cultivars with Sd1 malts have a proportion of free β-amylase less than 50% (usually from 30% to 40%) of total whereas Sd2 types have free to total β-amylase (F/T) ratios greater than 50% (usually between 62% and 78%). These polymorphisms are also correlated with forms of β-amylase in the developing grain, although, in the latter, Sd1 cultivars can be divided into two types, Sdd and Sde which cannot be distinguished either in malts or on the basis of F/T ratio. Unusual F/T ratios of an intermediate type (approximately 50%) and a very low type (under 30%) also occurred in these experiments. These may result from environmental effects or may be new genetic types.
TL;DR: In this paper, a differential method was proposed to estimate the glucose content of a total acid hydrolysate of an extract of barley extract, and the α-glucan content similarly determined after treatment of the extract with amyloglucosidase.
Abstract: The method described involves a differential assay in which the glucose content of a total acid hydrolysate of an extract of barley is estimated by glucose oxidase, and the α-glucan content similarly determined after treatment of the extract with amyloglucosidase. The difference between these estimations represents the glucose derived from β-glucan. The method provides reproducible results which are relatively insensitive to minor variations in the assay conditions, apart from temperature of extract preparation.
TL;DR: Numerous strains of Hafnia protea (originally Obesumbacterium proteus) were grown in brewer's wort in the absence and presence of Saccharomyces cerevisiae and gave rise to increased levels of n-propanol, isobutanol, isopentanol, dimethyl sulphide, dim methyl disulphide and 2,3-butanediol in finished beer.
Abstract: Numerous strains of Hafnia protea (originally Obesumbacterium proteus) were grown in brewer's wort in the absence and presence of Saccharomyces cerevisiae. The presence of H. protea gave rise to increased levels of n-propanol, isobutanol, isopentanol, dimethyl sulphide, dimethyl disulphide and 2,3-butanediol in finished beer. Concentrations of dimethyl sulphide and dimethyl disulphide varied according to the bacterial strains, but the increased levels of fusel alcohols and 2,3-butanediol were strain-independent.
TL;DR: In this article, the relative merits of profile tasting and difference tasting are discussed and the importance of profile analysis can reveal and characterize flavour differences that are not revealed by difference tasting using the triangular or three-glass test.
Abstract: The relative merits of profile tasting and difference tasting are discussed. Profile analysis can reveal and characterize flavour differences that are not revealed by difference tasting using the triangular or three-glass test, even though the same people carry out both types of test. A multiple comparison test is used in conjunction with profile analysis to reveal the size as well as the nature of perceived differences in flavour. This is exemplified by studies of the effect of adding increasing amounts of diacetyl to three different types of beer. It may be necessary to consider not just the presence of individual flavour notes but also their duration and order of perception in order to explain the effects of flavour potentiators, such as guanosine 5′-monophosphoric acid.
TL;DR: α-Amylase, extracted from Conquest barley harvested during the period 7 to 10 days after anthesis, was purified using acetone fractionation, glycogen complex formation and ion exchange chromatography and the specific activity of the enzyme was increased 750-fold during purification.
Abstract: α-Amylase, extracted from Conquest barley harvested during the period 7 to 10 days after anthesis, was purified using acetone fractionation, glycogen complex formation and ion exchange chromatography. The specific activity of the enzyme was increased 750-fold during purification. The purified α-amylase was homogeneous and free of other starch-metabolizing enzymes. Changes in enzyme activity and stability with pH and temperature were studied and the molecular weight and isoelectric point of the enzyme were determined.
TL;DR: In this article, a method based on the change in pH of a general purpose growth medium appears to offer the advantages of both time and sensitivity over methods currently in use and their relevance to improved brewery quality control methods is assessed.
Abstract: Recent developments in the rapid detection of low concentrations of micro-organisms are discussed and their relevance to improved brewery quality control methods is assessed.
A method based on the change in pH of a general purpose growth medium appears to offer the advantages of both time and sensitivity over methods currently in use.
TL;DR: In this article, a procedure for estimating the free fatty acids in wort and beer by gas liquid chromatography was described, and the reproducibility of the method was assessed by analysing replicate samples of wort.
Abstract: A procedure is described for estimating the free fatty acids in wort and beer by gas liquid chromatography. The free fatty acids with carbon number 8 to 18 are estimated simultaneously from one injection, and by including two internal standards the reproducibility of the method is maintained over the whole range. It has been demonstrated that other lipid materials such as glycerides and esters of fatty acids do not interfere with the assay. Compared with other methods, this procedure is fairly rapid and is suitable for routine purposes. The reproducibility of the method has been assessed by analysing replicate samples of wort and beer and the precision in estimating individual fatty acids is given.
TL;DR: Yeasts in the National Collection of Yeast Cultures showed substantial variation in biochemical and morphological properties following maintenance by conventional subculturing for prolonged periods, while brewing performance remained unchanged.
Abstract: Yeasts in the National Collection of Yeast Cultures showed substantial variation in biochemical and morphological properties following maintenance by conventional subculturing for prolonged periods. Variation was greatly diminished in yeasts maintained by freeze-drying. Although the initial viability of cultures immediately after freeze-drying had not always been high, only a very small subsequent decrease in viability has been detected after storage for periods of between 10 and 20 years.
Detailed study of the properties of brewing yeasts following prolonged storage in the freeze-dried state showed that brewing performance remained unchanged.
TL;DR: One-dimensional affinity electrophoresis and crossed immuno-affinoelectrophoreis with concanavalin A have been applied to show that esterase and acid phosphatase from barley malt are glycoprotein enzymes containing glucose or mannose in their carbohydrate part.
Abstract: One-dimensional affinity electrophoresis and crossed immuno-affinoelectrophoresis with concanavalin A have been applied to show that esterase and acid phosphatase from barley malt are glycoprotein enzymes containing glucose or mannose in their carbohydrate part. The enzymes retained their enzymic activity after binding in macromolecular complexes with concanavalin A. Indications were found of micro-heterogeneity within the carbohydrate moiety of the esterase.
TL;DR: Radiochemical experiments indicated that most of the free hydrogen sulphide excreted by a brewing yeast in wort and by Zymomonas anaerobia in beer was derived from sulphate, which stimulated sulphide production by the bacterium.
Abstract: Radiochemical experiments indicated that most of the free hydrogen sulphide excreted by a brewing yeast in wort and by Zymomonas anaerobia in beer was derived from sulphate. Sulphate was also assimilated by the organisms but most of their cellular sulphur was derived from other sources. In a synthetic beer medium, excessive amounts of hydrogen sulphide were liberated by Z. anaerobia when pantothenate was deficient. Sulphate and zinc ions stimulated sulphide production by the bacterium.
TL;DR: The authors showed that bromate concentration is highest at the embryo end, lowest in the middle and has an intermediate concentration at the distal end of the grain. But they did not find any evidence of bromates in kilned malt.
Abstract: Bromate applied to steeped barley enters the grain rapidly, within 4 h of application; it is reduced to bromide as germination proceeds but persists in the endosperm in measurable quantities until kilning. Bromate has not been detected in kilned malt.
Examination of lateral sections of grain shows that bromate concentration is highest at the embryo end, lowest in the middle and has an intermediate concentration at the distal end. These results, obtained with selected undamaged grains of both Proctor barley and Nackta (a naked variety), suggest that bromate can enter the grain at the distal end and over the grain surface as well as through the embryo.
TL;DR: In this paper, the authors add tergitol to de-aerated malt wort of ergosterol dispersed in the non-lipid detergent Tergitol, which allows satisfactory growth of oxygen-requiring cells of brewing yeast.
Abstract: Addition to de-aerated malt wort of ergosterol dispersed in the non-lipid detergent Tergitol allows satisfactory growth of oxygen-requiring cells of brewing yeast. Any nutritional requirement for unsaturated fatty acid for viability and growth of such cells (as distinct from effect on metabolite balance, e.g. of esters) can therefore be supplied by the normal constituents of a typical malt wort.
TL;DR: It is doubtful, therefore, whether the creation of two distinct species of Zymomonas within this genus is valid.
Abstract: Isolation from beer of a sucrose-fermenting species of Zymomonas confirmed as Z. mobilis, is recorded. Motility and H2S production were variable and sensitive to precise environmental conditions. The beer-spoilage potential of this species was established as limited. A strain of Z. anaerobia was isolated which acquired sucrose-fermenting ability after growth in fructose. It is doubtful, therefore, whether the creation of two distinct species within this genus is valid.