A Comparative Study of Stout Beer Batch Fermentation Using Free and Microencapsulated Yeasts

Because many questions arise regarding the use of immobilization technology to consistently produce a high quality beer, this work focuses on the effects of using an immobilization matrix in the fermentation process. The aim of this study was to explore the feasibility and potential uses of immobilization on sensorial characteristics such as color, flavor, and headspace compounds of stout beer, when using batch fermentation. Batch production of beer was conducted as a standard ale process for stout beer production. For the immobilized yeasts fermentation, cells were microencapsulated in alginate, by using the Thiele modulus procedure for microcapsule design. Glucose concentration, cell multiplication, cell viability, specific gravity, pH, Brix, and ethanol were monitored throughout the fermentation process. Both, sensorial analysis (statistic triangle tests) and instrumental methods (gas chromatography to measure headspace compounds and visible spectrophotometer to quantify the color) were used to evaluate characteristics of the beer that was produced from immobilized and free yeast fermentations. Free and immobilized yeasts fermentation showed no significant difference (p > 0.05) for all variables of interest. The profile of headspace compounds was different, perhaps because of changes in yeast’s behavior and the presence of secondary metabolites. However, immobilization did not have a significant impact on the beer flavor, as detected by the sensorial triangle test.     

以甘蔗固定化酵母发酵低醇葡萄酒的研究

试验以甘蔗为载体材料,研究了用甘蔗块固定化酵母在低醇贵人香葡萄酒发酵中的表现,检测了其对发酵时间,酒精度,稳定性及发酵批次等的影响,同时定量分析了固定化前后酵母发酵低醇酒在香气成分上变化.结果发现,以甘蔗为载体固定化酵母应用到低醇酒发酵,可以有效地控制低醇葡萄酒的理想酒精度,增加产品的稳定性.而且甘蔗固定化酵母减少了酒中高级醇的含量,增加了低醇葡萄酒的复杂香气和口感.     

ETHANOL FERMENTATION OF VARIOUS RED RICES WITHOUT COOKING

With various red rices as raw material, fermentation without cooking was allowed to proceed at pH 4.0 and 30°C for 4 d for production of novel alcoholic beverages. Ethanol fermentation was achieved with various rice grains. In particular, uncooked wild-rice (Zizania aquatica) is reported now for the first time as being used for ethanol fermentation. The final concentration of ethanol achieved during fermentation was 8.8–9.3% (v/v). Rice wine made from aromatic red rice (Oryza sativa var. Indica, Tapol) had a wine-like red color. It was rich in a fruity aroma and had a characteristic sour taste, as revealed by organoleptic testing. Volatile substances formed have been analysed by gas chromatography. Rice wine made from black rice (Oryza sativa var. Indica) also had a wine-like red color and a sour taste. By contrast, rice wines made from red rice (Oryza sativa var. Japonica) and wild-rice were faintly yellow in color and had a sake-like and a somewhat green tea-like flavor, respectively. Although the red pigments of the aromatic red rice and black rice were solubilized during uncooked ethanol fermentation, the pigments of red rice and wild-rice were insoluble and not available as material for brewing of red-colored alcoholic beverages. Aromatic red rice appears to be a suitable material for the production of a wine-like alcoholic beverage.     

Production of white wine by Saccharomyces cerevisiae immobilized on grape pomace

White wine was produced with Saccharomyces cerevisiae cells immobilized on grape pomace, by natural adsorption. The support, the main solid waste from the wine industry, consisted of the skins, seeds and stems. Immobilization was tested using different media, namely complex culture medium, raw grape must and diluted grape must. Grape pomace was revealed to be an appropriate support for yeast cell immobilization. Moreover, grape must was shown to be the most suitable medium as immobilized cells became adapted to the conditions in the subsequent alcoholic fermentation in the wine‐making process. The wines produced, either with immobilized cells or with free cells, were subjected to chemical analysis by HPLC (ethanol, glycerol, sugars and organic acids) and by gas chromatography (major and minor volatile compounds); additionally, colour (CIELab) and sensory analysis were performed. The use of immobilized systems to conduct alcoholic fermentation in white wine production proved to be a more rapid and a more efficient process, especially when large amounts of SO₂ were present in the must. Furthermore, the final wines obtained with immobilized cells demonstrated improved sensory properties related to the larger amounts of ethanol and volatile compounds produced. The more intense colour of these wines could be a drawback, which could be hindered by the reutilization of the biocatalyst in successive fermentations. Copyright © 2012 The Institute of Brewing & Distilling     

YEAST AND ITS EFFECT ON THE FLAVOUR OF ALCOHOLIC BEVERAGES*

Sensory examination of an aroma model consisting of alcohols, fatty acids, esters and aldehydes, in concentrations estimated in whisky, has proved that—in addition to vicinal diketones—esters predominate as components influencing the aroma, but also some fatty acids exercise a most marked influence. Furthermore, some people possess a good ability to smell certain compounds whereas others cannot smell them as well, but detect other compounds more easily. Within the group of more than 100 identified aroma components, mainly the same substances appear in the volatile aroma fraction of beer, wine and distilled beverages. In view of this, it seems evident that the raw materials utilized for the production of the beverages contribute to no more than a limited extent towards the aroma composition. The aroma components which are most noticeable are produced by the yeast during fermentation, and the nature of the final aroma first and foremost depends upon the kind of yeast used, and upon the fermentation conditions. Although the yeast for the most part produces the same aroma components also In different beverages, considerable variation may occur in the quantities of aroma components even in beverages of the same type. The structure and function of the plasma membrane selectively regulate the uptake of different compounds from the medium into the yeast cell, and the release of the metabolites from the cell into the medium. In this sense, the lipid composition of the plasma membrane and its lipolytic enzymes may possess a decisive importance. The activity of the lipolytic enzymes present in the plasma membrane must be controlled by some regulatory mechanism. If this is the case, the permeability of the plasma membrane can be modified, e.g., by activation of the phospholipases, with consequent degradation of membrane phospholipids. Consequently, it is likely that one of the functions of the lipolytic enzymes present in the plasma membrane is that of participation in the transport processes by changing the permeability properties of the plasma membrane.     

黄酒固定化发酵过程及香气物质形成的研究

将黄酒酵母用海藻酸钙包埋制成固定化酵母,研究游离酵母与固定化酵母的黄酒发酵过程理化指标和香气物质生成量的差异,结果表明:经过主发酵5 d(28℃),后发酵15 d(15℃),固定化酵母发酵过程的酒精度、总糖、总酸变化曲线与游离发酵过程曲线差异不大,固定化酵母发酵性能稳定,杂菌污染可控。用气相色谱(GC)分析乙酸乙酯等9种黄酒特征性香气物质,发现游离发酵黄酒正丙醇、异丁醇、异戊醇、β-苯乙醇的总高级醇含量为680.91 mg/L,固定化发酵第1,2,3,4,5批黄酒的总高级醇含量分别为633.63,649.79,658.17,637.63,614.68 mg/L,说明固定化发酵有利于控制黄酒中的高级醇含量。固定化发酵酯类总量高于游离酵母,且随着固定化酵母发酵批次的增加而递增,即:固定化第5批(115.90 mg/L)>第4批(90.81 mg/L)>第1~3批(80.10~81.81 mg/L)>游离酵母(55.66 mg/L),表明固定化发酵使黄酒的酯类香气愈加浓郁。根据香气阈值计算的固定化发酵酿得的黄酒的香气不比游离酵母酿得的黄酒差,固定化酵母发酵生产黄酒有商业化应用的前景。     

Growth and by‐product profiles of Kluyveromyces marxianus cells immobilized in foamed alginate

The aim of this research was to study how the yeast cell immobilization technique influences the growth and fermentation profiles of Kluyveromyces marxianus cultivated on apple/chokeberry and apple/cranberry pomaces. Encapsulation of the cells was performed by droplet formation from a foamed alginate solution. The growth and metabolic profiles were evaluated for both free and immobilized cells. Culture media with fruit waste produced good growth of free as well as immobilized yeast cells. The fermentation profiles of K. marxianus were different with each waste material. The most varied aroma profiles were noted for immobilized yeast cultivated on apple/chokeberry pomace. Copyright © 2014 John Wiley & Sons, Ltd.     

Yeasts and their importance to the flavour of traditional Chinese liquor: a review

As one of the three major distilled spirits in the world, traditional Chinese liquor has a distinctive aroma and taste. The brewing process typically involves two stages: the Daqu‐making process and the liquor‐making process. Further, it commonly adopts solid state fermentation in an open environment, which involves diverse microorganisms such as bacteria and fungi. Yeasts, as an integral brewing microorganism, are not only a dominant force in the fermentation process but also play a key role in the quality and character of different flavour liquors. Studies on yeasts associated with Chinese liquor have rarely compared them with those associated with other alcoholic beverages (wine, sake, etc.), especially in the microbiome‐related flavour of the alcoholic beverage. Here, we review the Chinese liquor brewing process, the yeast community in the brewing process, the yeast derived flavour compounds, the interaction between yeasts and other microorganisms and gene level modifications. © 2019 The Institute of Brewing & Distilling     

Research progress on the application of different controlling strategies to minimizing ethyl carbamate in grape wine

Ethyl carbamate (EC) is a probable carcinogenic compound commonly found in fermented foods and alcoholic beverages and has been classified as a category 2A carcinogen by the International Agency for Research on Cancer (IARC). Alcoholic beverages are one of the main sources of EC intake by humans. Therefore, many countries have introduced a standard EC limit in alcoholic beverages. Wine is the second largest alcoholic beverage in the world after beer and is loved by consumers for its rich taste. However, different survey results showed that the detection rate of EC in wine was almost 100%, while the maximum content was as high as 100 μg/L, necessitating EC content regulation in wine. The existing methods for controlling the EC level in wine mainly include optimizing raw fermentation materials and processes, using genetically engineered strains, and enzymatic methods (urease or urethanase). This review focused on introducing and comparing the advantages, disadvantages, and applicability of methods for controlling EC, and proposes two possible new techniques, that is, changing the fermentation strain and exogenously adding phenolic compounds. In the future, it is hoped that the feasibility of this prospect will be verified by pilot-scale or large-scale application to provide new insight into the regulation of EC during wine production. The formation mechanism and influencing factors of EC in wine were also introduced and the analytical methods of EC were summarized.     

Production of indigenous alcoholic beverages in a rural village of Tanzania

In this study, the production techniques of indigenous alcoholic beverages in a rural village in Tanzania were investigated. In the village, three different kinds of alcoholic beverages were produced: a maize turbid beer (komoni), a straw beer (kimpumu) and a hybrid straw beer (kiambule). In the course of the production of these three alcoholic beverages, two different kinds of porridge, a fermented porridge (nyambo) as a source of yeasts and a sweet porridge (kikonde) as a source of saccharides, were produced. These porridges were mixed at the end of the production process. The pH value of fermented porridge was kept below 4 during its preparation. This was effective in preventing contamination of the porridge by harmful bacteria and in stabilizing the growth of the yeasts. Sweet porridge was heated in the range of 50–70 °C and this enhanced the saccharification of the starch in the raw materials. The starting materials of these alcoholic beverages were finger millet and maize. Germinated finger millet, which has a high amylase activity compared with other cereals, was used as an amylase source in each of the alcoholic beverage production processes. Various techniques to enhance and stabilize the quality of the indigenous alcoholic beverages are described. Copyright © 2014 The Institute of Brewing & Distilling     

啤酒酵母酿造葡萄酒及香气成分GC-MS分析研究

以宁夏贺兰山东麓产区酿酒葡萄为原料酿造葡萄酒,测定其感官指标、理化指标,并通过顶空固相微萃取-气质联用（HS- SPME-GC-MS）技术分析啤酒酵母单独发酵（SY）、葡萄酒酵母单独发酵（AY）及二者混菌（1∶1）发酵（MY）酿造葡萄酒的香气物质,并计算气味活力值（OAV）。结果表明,3个样品的感官评分顺序依次为MY＞SY＞AY,理化指标符合相关国标;MY、SY、AY样品GC-MS分析分别共检测出22种、20种、15种香气成分,其中含量最高的均为异戊醇,MY、SY样品中的酯类成分较AY样品种类多;OAV分析结果进一步显示,对3个样品香气贡献最大的物质均为酯类,MY样品OAV＞1的香气成分为4种。啤酒酵母酿造的葡萄酒风味独特,并且混菌发酵可以提升葡萄酒品质。     

Interactions between yeast, oxygen and polyphenols during alcoholic fermentations: Practical implications

During alcoholic fermentation, even when Saccharomyces cerevisiae cells have used the required oxygen for lipid synthesis, they can consume much more oxygen with no detrimental effect on the fermentation process. Under these conditions, most of the superfluous oxygen is consumed by yeasts by the partial functioning of several nonrespiratory oxygen consumption pathways, which are characterized by the production of reactive oxygen species (ROS). When excess oxygen is added to yeast cells, cell sterol content decreases, following the strong oxidation of intracellular sterols. During aging of fermented products in the presence of nonviable yeast lees (harvested at the end of alcoholic fermentation), the lees can consume oxygen for at least 3 years of the aging process. This oxygen consumption by yeast lees is related to moderate oxidation of yeast membrane lipids by the action of free radicals, strongly decreasing sterols in the yeast lees. The biochemical reactions involved in the oxygen consumption pathways during alcoholic fermentation may be the same as those responsible for oxygen consumption observed in yeast lees. Therefore, the cross-reactivity of complex plant polyphenols, tannins and yeast towards oxygen can easily occur during technological processes (alcoholic fermentation and wine aging). The micro-oxygenation of yeasts releases ROS during alcoholic fermentation and may favour the oxidation of wine phenolic compounds. As yeasts have much higher affinities for oxygen than plant polyphenols, viable yeast and yeast lees compete with phenolic compounds and then hinder the wine aging process. Also, the partial adsorption of plant polyphenols on yeast occurs during alcoholic fermentation, which modifies the overall reactivity of yeast and polyphenols towards oxygen.     

Estimation of sulphite in food in France.

Estimates have been made of the consumption levels of sulphites in foods in France using two methods, a global and a segmented protocol. The global method gave an estimated average intake of 20 mg SO2/day/capita; the segmented method gave estimates of 1.96 mg/day/capita for non-consumers of alcoholic beverages and 31.5 mg/day/capita for average consumers of cider, beer and wine. The risk of exceeding the Acceptable Daily Intake concerns only regular consumers (40-75 years old) of alcoholic beverages, particularly wine, the main vector. The global approach appears to be a simple and useful method for estimating intakes.     

Ethyl carbamate in the production and aging of cachaça in oak (Quercus sp.) and amburana (Amburana cearensis) barrels

There are residual organic and inorganic contaminants in the cachaça production chain. Among the organic contaminants, ethyl carbamate has been widely studied. It is formed naturally during the fermentation processes and can be found in many foods and beverages such as bread, yoghurt, wine, beer and especially in fermented–distilled beverages such as whiskey, rum, vodka, grappa, cachaça and tiquira. The objective of this study was to identify and quantify ethyl carbamate during the steps of the production process and aging of cachaça in oak (Quercus sp) and amburana (Amburana cearensis) barrels. The cane used for cachaça production, as well as the process for obtaining the fermentation broth, did not affect the formation of ethyl carbamate, as it was not detected. Carbamate was detected in low concentrations, but was not quantified, in the fermentation, distillation and aging steps. Copyright © 2014 The Institute of Brewing & Distilling     

苹果酒香气成分研究进展

苹果酒是苹果深加工的主要产品之一。香气是苹果酒风味的重要因素。文章中综述了苹果品种、酵母和发酵条件等因素对苹果酒香气形成的研究进展 ,并对今后此方面的研究提出了建议     

Function and regulation of yeast genes involved in higher alcohol and ester metabolism during beverage fermentation

The biochemical formation of yeast-derived sensory-active metabolites like higher alcohols and esters determines the different characteristics of aroma and taste in fermented beverages. In yeast fermentation process, a large number of environmental factors affecting the production of volatile aroma compounds are abundant. Factors like substrate composition in fermentation media as well as process parameters influencing these flavor-active metabolites have already been described. These factors can act on the expression of yeast genes involved in aroma metabolism resulting in concentration differences in esters and higher alcohols important for flavor and taste. The understanding of the function of genes involved in biosynthetic pathways of aroma-active substances as well as their regulatory mechanisms is needed to control the production of ester and higher alcohol synthesis to create specific aroma profiles in fermented beverages. This review discusses the known regulation and function of several individual genes (ATF1, ATF2, EEB1, EHT1, BAT1, BAT2 and BAP2) described in fusel alcohol and ester synthesis mainly in S. cerevisiae and S. pastorianus var. carlsbergensis. Also, different factors like oxygen and temperature that allow ester and higher alcohol synthesis to be controlled during yeast fermentation are described.     

Enhancement of urea uptake in Chinese rice wine yeast strain N85 by the constitutive expression of DUR3 for ethyl carbamate elimination

Most of the fermented alcoholic beverages, particularly Chinese rice wine, contain the potentially human carcinogenic compound ethyl carbamate (EC). As a major EC precursor in Chinese rice wine, urea in fermentations can be transported into the yeast cell by urea permease and finally metabolized by urea carboxylase and allophanate hydrolase in vivo. To eliminate EC in Chinese rice wines, the present study constructed high urea uptake yeast strains N1‐D, N2‐D and N‐D, by introducing a strong promoter (PGK1p) into the urea permease gene (DUR3) of the industrial Chinese rice wine yeast N85, and by the restoration of the URA3 gene at the same time. With these self‐cloned, high urea uptake strains, the urea and EC in the terminal Chinese rice wine samples were reduced to different extents. With two copies of overexpressed DUR3, the N‐D strain could reduce the urea and the EC by 53.4 and 26.1%, respectively. No difference in fermentation characteristics was found between the engineered strains and the parental industrial yeast strain N85. These results could help to optimize the genetic manipulation strategy for EC elimination in Chinese rice wine production. Copyright © 2015 The Institute of Brewing & Distilling     

发酵过程中添加磷酸氢二铵对苹果酒香气物质的影响

以富士苹果为原料,分别在发酵前、酵母生长对数期和稳定期前期添加280 mg/L的磷酸氢二铵（DAP）,研究DAP的添加对酵母发酵性能和苹果酒香气物质的影响。结果表明,发酵过程中添加DAP可加快酵母发酵速率,在酵母发酵前和酵母生长对数期添加DAP显著降低了琥珀酸含量（P＜0.05）;在稳定期前期添加DAP显著降低了苹果酸含量（P＜0.05）,总香气含量最高（11.09 mg/L）,更有利于苹果酒中挥发性香气化合物的合成,但对酵母数影响不大。     

NITROSAMINES IN ALCOHOLIC BEVERAGES

A limited survey was carried out to determine the nitrosamine content of several varieties of alcoholic beverages (beer and ale, whiskey, wine, cider, etc.) sold in Canada. Of 22 samples of different beers and ales analyzed all but one contained traces of dimethylnitrosamine; the overall mean level found was 1.5 ppb. Only one Canadian rye and one Scotch whiskey out of a total of 13 samples contained traces of either dimethylnitrosamine or diethylnitrosamine. All the 8 wines and 7 cider samples were negative.     

天然固定化酵母载体在果酒中的发酵试验研究

采用海藻酸钠、甘蔗渣、玉米芯、干红枣4种材料作为酵母菌的固定化载体在香蕉果酒中进行发酵试验,结果表明,无论从载体的制备、酵母的连续发酵能力以及酒液的感官品质,天然甘蔗渣载体均具有其优越性,为果酒生产提供高效优质的酵母固定化载体.