High gravity primary continuous beer fermentation using flocculent yeast biomass

The current work assessed a new immobilized cell reactor system throughout a long‐term (54 days) continuous primary fermentation of lager‐type wort of high specific gravity. The experiment was performed in a 4 L airlift bioreactor and immobilization of biomass was attained solely by flocculation. Despite the constant liquid agitation and washout of biomass, up to 53 g dry wt/L of yeast remained immobilized in the system. Two types of beer were produced without interrupting the reactor, based on two types of wort: a Pilsener type with high specific gravity of 15.6 ± 0.3°P; and a dark lager wort with specific gravity of 14.4 ± 0.03°P. Even during the inlet of high gravity wort, the desired attenuation was achieved without the need for either recirculation or an auxiliary second stage bioreactor. The specific saccharide consumption rate was kept around 7.9 ± 0.4 g/L/h and ethanol productivity oscillated at 3.36 ± 0.2 g/L/h for nearly a month. During this period the volumetric productivity of the current bioreactor reached 1.6 L beer/L/day. The green beers produced from the Pilsener and dark lager worts met the standards of regular finished primary beer fermentation. The productivity of diacetyl through the entire experiment could be correlated to the free amino nitrogen consumption rate. Copyright © 2014 The Institute of Brewing & Distilling     

Continuous beer fermentation – diacetyl as a villain

This work tested the viability of producing beer of good quality after maturation of green beer obtained by primary continuous fermentation of high‐gravity wort using an airlift bioreactor with flocculated biomass. Fermentation performance of the tested setup was unique as it reached a maximum saccharide consumption rate of 9.43 g L^?1 h^?1 and an ethanol productivity of 3.75 g L^?1 h^?1. Despite the high levels of diacetyl present in the green beer, a regular maturation was able to reduce it to below threshold values in up to 15 days. It was observed that diacetyl production was strongly correlated with wort composition injected into the system, rather than with the large amount of biomass immobilized in the bioreactor (up to 727 × 10⁶ cell mL^?1). Organoleptic tests showed that the maturated beer had no major defects. Copyright © 2015 The Institute of Brewing & Distilling     

Carrier‐free,continuous primary beer fermentation

Developing a sustainable continuous fermentation reactor is one of the most ambitious tasks in brewing science, but it could bring great benefits regarding volumetric productivity to modern breweries. Immobilized cell technology is often applied to reach the large densities of yeast needed in a continuous fermentation process. However, the financial cost associated with the use of carriers for yeast immobilization is one of the major drawbacks in the technology. This work suggests that yeast flocculation could address biomass immobilization in a gas‐lift reactor for the continuous primary fermentation of beer. Nearly 25 g dry wt L^?1 of yeast was flocculated in the reactor before interruption of the fermentation. Stable sugar consumption and ethanol production (4.5% alcohol by volume) from an 11°P wort was evidenced. The key esters and higher alcohols measured in the young beer met the standards of a finished primary beer fermentation. Copyright © 2014 The Institute of Brewing & Distilling     

The effect of wort aeration on fermentation,maturation and volatile components of beer produced on an industrial scale

The aim of the study was to determine the effect of the initial beer wort aeration on the process of fermentation, maturation, content of the volatile components of beer and abundance and vitality of yeast biomass. The experiments were performed on an industrial scale, with fermentation and maturation performed in fermentation tanks with a capacity of 3800 hL. The wort was aerated with sterile air in quantities as follows: 7, 10 and 12 mg/L. During fermentation and maturation, the changes in the content of the extract, yeast growth and vitality and more importantly volatile components were investigated. The experiments showed that differentiated aeration has a significant impact on the course of fermentation and metabolic changes. With the increase in wort aeration, the content of acetaldehyde decreased and the concentration of higher alcohols increased. On the other hand, the contents of esters and vicinal diketones did not change. The level of aeration did not affect the final quality of beer. Copyright © 2017 The Institute of Brewing & Distilling     

FUNDAMENTALS OF IMMOBILISED YEAST CELLS FOR CONTINUOUS BEER FERMENTATION: A REVIEW

Recent fundamental research conducted on immobilised cells with a focus on continuous primary beer fermentation is presented in this review. The knowledge of whole-cell immobilisation, continuous fermentation, yeast biochemistry associated with beer flavour production, and bioreactor engineering design is required to apply immobilised yeast cells for industrial scale beer production. Understanding how immobilisation and continuous bioreactor operation affect yeast cell metabolism and viability will provide the groundwork for optimising beer quality. The latest studies on immobilised cell carriers, viability, vitality, mass transfer characteristics and bioreactor design indicate that an industrial scale immobilised cell system for primary beer fermentation may soon be a reality in the modern brewery .     

High Gravity Brewing by Continuous Process Using Immobilised Yeast: Effect of Wort Original Gravity on Fermentation Performance

The present work evaluated the influence of all‐malt wort original gravity on fermentative parameters and flavour‐active compound formation during primary fermentation of high gravity brewing by a continuous process using a lager yeast immobilised on a natural carrier obtained from brewer's spent grain (the main brewery by‐product). The all‐malt worts with original gravity (OG) ranging from 13.4 to 18.5°Plato were prepared by diluting a very‐high‐gravity wort (20°Plato) with sterile brewery water. The continuous assay was carried out in a bubble column bioreactor with a total working volume of 5.2 litres, at 15°C, using a constant gas flow rate of 250 mL/min (200 mL/min of CO₂ and 50 mL/min of air) and a dilution rate of 0.04 h^?1 (residence time of 25 h). The results indicated that as the wort OG was increased, the ethanol concentration of the outflowing beer increased. On the other hand, the continuous fermentation of the most concentrated worts (16.6 and 18.5°Plato) resulted in beers with unbalanced flavour profiles due to excessive ethyl acetate formation. The immobilised cell concentration appeared to be nearly independent from increasing wort OG.     

Influence of temperature on continuous high gravity brewing with yeasts immobilized on spent grains

Flavor compounds’ formation and fermentative parameters of continuous high gravity brewing with yeasts immobilized on spent grains were evaluated at three different temperatures (7, 10 and 15 °C). The assays were performed in a bubble column reactor at constant dilution rate (0.05 h⁻¹) and total gas flow rate (240 ml/min of CO₂ and 10 ml/min of air), with high-gravity all-malt wort (15°Plato). The results revealed that as the fermentation temperature was increased from 7 to 15 °C, the apparent and real degrees of fermentation, rate of extract consumption, ethanol volumetric productivity and consumption of free amino nitrogen (FAN) increased. In addition, beer produced at 15 °C presented a higher alcohols to esters ratio (2.2–2.4:1) similar to the optimum values described in the literature. It was thus concluded that primary high-gravity (15°Plato) all-malt wort fermentation by continuous process with yeasts immobilized on spent grains, can be carried out with a good performance at 15 °C.     

高浓高温对啤酒酵母发酵性能的影响

以啤酒酵母S-6为实验菌株,研究了主发酵温度和原麦汁浓度对啤酒发酵的残糖、酒精度、风味物质和絮凝性等性能指标的影响。结果表明,原麦汁浓度一定时,主发酵温度对高级醇和乙酸酯的含量影响较大,主发酵温度由10 ℃提高至16 ℃时,高级醇含量提高了10%～20%,乙酸酯含量提高了8%～16%,但CO2累积质量损失、残糖、酒精度和絮凝性基本不受温度的影响;主发酵温度一定时,原麦汁浓度对酵母絮凝性影响较大,原麦汁浓度越高,酵母絮凝性越低,将高浓（18 °Bx）发酵液稀释50%至常浓（12 °Bx）,残糖、酒精度和高级醇的含量与常浓发酵液基本相同。该研究为选育高温高浓发酵低产高级醇同时强絮凝性酵母菌株提供了重要依据。     

麦汁缓冲性能对啤酒酵母高级醇生成量的影响

在麦汁主要成分给定的情况下，水质、外加酸以及麦汁煮沸时间是影响麦汁缓冲容量的重要因素，缓冲容量愈大，高级醇含量愈高。结果表明：pH5．0的酸水糖化效果较好；较大缓冲容量的水质有利于麦芽的糖化；盐酸、磷酸和乳酸的使用能提高麦汁的缓冲容量；充分的煮沸可使其缓冲容量降低30％以上；麦汁的缓冲容量对啤酒中高级醇浓度有较大的影响，可以通过控制麦汁的缓冲容量来实现对发酵过程pH的控制。     

啤酒酵母代谢副产物高级醇的影响因素研究进展

高级醇是啤酒酿造过程中产生的副产物的主要成分,是啤酒的主要香味和口味物质之一。高级醇的生成途径有降解代谢和合成代谢两种。适量的高级醇能赋予啤酒丰满的香味和口味,增加酒体的协调性,但过量存在也是啤酒异杂味的主要来源之一。高级醇含量超过100mg／L会使啤酒口味和受欢迎程度明显降低,啤酒中高级醇含量的标准值为：下面发酵啤酒60～90mg／L;上面发酵啤酒〈100mg／L。高级醇含量主要受酵母菌种、麦汁成分以及发酵工艺条件的影响．因此生产过程应控制好这几个因素。     

降低高浓啤酒发酵中高级醇含量的研究

为降低高浓啤酒发酵中高级醇的生成量,研究18°Bx麦汁啤酒酿造过程中的加糖浆方式、酵母接种量和麦汁中α-氨基氮含量对啤酒高级醇生成量的影响。结果表明：18°Bx麦汁发酵高级醇生成量显著高于12°Bx麦汁;分两次加入制备18°Bx麦汁所需的糖浆量、控制18°Bx麦汁的酵母细胞接种量为3×107个/mL以及麦汁中α-氨基氮含量为230mg/L麦汁时,均有利于降低18°Bx高浓啤酒发酵过程中高级醇的生成量。     

Alpha Amino Nitrogen and Fusel Alcohols of Sorghum Worts Fermented into Lager Beer

The levels of alpha amino nitrogen (AAN) and fusel alcohols during fermentations of lager worts produced from waxy sorghum grits either inoculated with yeast cultured in wort or yeast-malt media were performed. Worts produced from waxy sorghum grits had comparable AAN to commercial wort. The oxygen concentration in the reactor headspace changed from 20% at the beginning of fermentation to less than 1% after 72 hrs fermentation indicating a gradual change from aerobic to anaerobic conditions. The utilization of AAN for production of propanol, isobutanol and amyl-isoamyl alcohols from waxy sorghum grits was comparable to a control wort. Production of propanol, isobutanol and amyl-isoamyl alcohols followed the same trend over 144 hr fermentation. Isobutanol was produced in the lowest concentration. The initiation of propanol production occurred after 24 and 36 hr fermentation for worts inoculated with yeast cultured in wort and yeast-malt media, respectively. The final concentration of ethanol and fusel alcohols were within the expected range found in commercial beers. Worts produced from barley malt and waxy sorghum grits were an adequate substrate for Saccharomyces cerevisiae, and were comparable to a commercial wort. The utilisation of refined waxy sorghum grits as brewing adjuncts for lager beers was demonstrated.     

The effect of pitching rate on fermentation,maturation and flavour compounds of beer produced on an industrial scale

The aim of the study was to determine the effect of the initial number of yeast cells in the wort on the process of fermentation, maturation and the content of the volatile components of beer, as well as the viability and vitality of the yeast biomass. The experiments were performed on an industrial scale, with fermentation and maturation in cylindro‐conical fermentation tanks with a capacity of 3800 hL. Yeast for pitching was collected after secondary fermentation (third passage) and wort pitching levels were 5 × 10⁶, 7 × 10⁶ and 9 × 10⁶ cells/mL. During fermentation and maturation, the changes in the content of the extract, yeast growth, yeast vitality and selected volatile components were investigated. Experiments showed that the yeast inoculum had a significant impact on the course of the fermentation and metabolic changes. With increasing numbers of cells introduced into the wort, the content of the esters and fusel alcohols increased, while the acetaldehyde concentration decreased. These changes affected the final quality of the beer. Copyright © 2015 The Institute of Brewing & Distilling     

降低上面发酵小麦啤酒头痛感的酿造条件优化

啤酒上头的原因主要是较高的醇酯比和乙醛含量。为降低上面发酵小麦啤酒头痛感,对其发酵条件进行优化,并通过气相色谱（GC）检测啤酒中高级醇、酯类和乙醛等风味物质含量。结果表明,最优发酵条件为发酵温度18 ℃（醇酯比2.02、乙醛含量3.51 mg/L）、发酵压力0.12 MPa（醇酯比2.01、乙醛含量2.75 mg/L）和零代酵母（醇酯比2.20、乙醛含量2.76 mg/L）。在此条件下发酵的小麦啤酒醇酯比为2.0～2.5,乙醛含量＜4 mg/L,不易引起上头。     

A novel approach for the production of a non‐alcohol beer (≤0.5% abv) by a combination of limited fermentation and vacuum distillation

Despite the increasing demand, the production of non‐alcohol beers is still limited by unsatisfactory or artificial flavour and taste. In this study, a novel approach to producing non‐alcohol beer is presented, in which the alcohol‐reducing techniques, limited fermentation and vacuum distillation were combined. Starting from barley and wheat malts, wort with a low level of fermentable sugars was prepared by infusion mashing and lautering. Limited fermentation was carried out by Saccharomycodes ludwigii at 18°C. When the level of fermentable sugar was reduced by 25%, the fermented wort was quickly cooled from 18 to 0°C and held at that temperature for two days. The young beer was obtained after degassing and removal of yeast and was then subjected to vacuum distillation at 0.06 MPa to remove the alcohol. The concentrated extract is suitable for storage and transportation. The final product of non‐alcohol beer was obtained by dilution with deoxygenated water and carbonation with 6.0 g/L CO₂, followed by addition of 8–12% of regular beer and equilibration for 2–3 days to develop normal beer aroma. The results showed that the non‐alcohol beer had several favourable properties, including the alcohol level of <0.5% (v /v), colour 7.0 (EBC), thiobarbituric acid value of 1.05 and ratio of alcohols to esters of 1.08. Compared with other methods for the production of non‐alcohol beer, this novel approach produced a favourable alternative to regular beers with similar flavour characteristics and satisfactory stability. Copyright © 2017 The Institute of Brewing & Distilling     

HORACE BROWN MEMORIAL LECTURE A REALISTIC VIEW ON THE ROLE OF RESEARCH IN THE BREWING INDUSTRY TODAY

Present-day economic pressures stimulate technological innovations toward more rapid processing and to minimise both capital and production costs. Fermentation and maturation practices in most production plants are essentially unchanged from the low productivity batch processes. In terms of process economics two alternatives exist—moving to greater volume accelerated-batch processing and applying fully continuous high rate fermentation systems. Central to these issues are the growth controlling aspects of yeast performance in brewery fermentations. The importance of dissolved oxygen on lipid metabolism, yeast growth and beer flavour, the precise role of storage carbohydrates and the critical nature of the glycolytic/gluconeogenic junction in controlling fermentation performance are reviewed. The objectives of process optimisation are to build up sufficient yeast concentrations to gain optimal rate and extent of attenuation and desired flavour development whilst balancing but not over-expending wort nutrients for growth and maintenance. In this regard great promise may lie with new technologies including yeast oxygenation and immobilised cell systems. Particular emphasis is placed upon the ways in which this may be technically achieved and attention is drawn to the complexity of innovation management. Practical implications of factors benefiting and adversely affecting fermentation efficiency and beer flavour in both traditional and continuous immobilised cell systems are discussed.     

关于提高啤酒质量与稳定性有效途径的研究

获得良好的啤酒风味稳定性及混浊稳定性是酿造人员多年来治理致力要解决的问题,啤酒中的高级醇、醛类、双乙酰、有机酸、脂类及含硫化合物等对啤酒质量风味有着重要的影响作用,为了提高啤酒质量与改善和预防这些风味缺陷必须从原料、糖化、发酵、麦汁过滤、卫生管理等工序上进行控制。     

Application of Plackett–Burman experimental design for investigating the effect of wort amino acids on flavour‐active compounds production during lager yeast fermentation

Aroma‐active higher alcohols and esters are produced intracellularly in the cytosol by fermenting lager yeast cells, which are of major industrial interest because they determine aroma and taste characteristics of the fermented beer. Wort amino acid composition and their utilization by yeast during brewer's wort fermentation influence both the yeast fermentation performance and the flavour profile of the finished product. To better understand the relationship between the yeast cell and wort amino acid composition, Plackett–Burman screening design was applied to measure the changes in nitrogen composition associated with yeast amino acids uptake and flavour formation during fermentation. Here, using an industrial lager brewing strain of Saccharomyces pastorianus , we investigated the effect of amino acid composition on the accumulation of higher alcohols and volatile esters. The objective of this study was to identify the significant amino acids involved in the flavour production during beer fermentation. Our results showed that even though different flavour substances were produced with different amino acid composition in the fermentation experiments, the discrepancies were not related to the total amount of amino acids in the synthetic medium. The most significant effect on higher alcohol production was exercised by the content of glutamic acid, aromatic amino acids and branch chain amino acids. Leucine, valine, glutamic acid, phenylalanine, serine and lysine were identified as important determinants for the formation of esters. The future applications of this information could drastically improve the current regime of selecting malt and adjunct or their formula with desired amino acids in wort. Copyright © 2017 The Institute of Brewing & Distilling     

Maintaining yeast viability in continuous primary beer fermentation

Continuous fermentation is a long known and vastly studied process. The use of immobilized cell technology (ICT) is exploited in a significant number of studies owing to the associated high volumetric productivity, time savings and low capital demand. This work was aimed at solving one of the most relevant obstacles to implementing ICT on a large scale in beer fermentations, namely the control of biomass and the maintenance of cell viability in a gas‐lift bioreactor. For this purpose, foam fractionation by skimming was proposed as a tool for control of continuous biomass concentration. The consequences of foaming on lignocellulosic yeast carrier losses were assessed and discussed. A steady consumption of sugars from wort, as well as consistent ethanol production, were achieved. The viability of the suspended cells in the reactor was compared with that of the cell population in the foam using flow cytometry. Results suggest that foam might be used as a promising tool to skim non‐viable biomass out of the gas‐lift reactor, thus ensuring the maintenance of a cell culture with optimum viability. Copyright © 2014 The Institute of Brewing & Distilling     

Response surface methodology optimisation of immobilised Lactobacillus acidophilus banana puree fermentation

Fermentation temperature (34–40 °C), total inoculum level (1%–3%, v/v) and peeled-fruit-to-water ratio (12.5%–37.5%, w/v) were combined to study their effects on the fermentation of banana media by free and Ca-alginate or κ-carrageenan-immobilised Lactobacillus acidophilus. A three-variable and three-level design method, analysed by response surface methodology (RSM), was used. These factors, except peeled-fruit-to-water ratio, were found to be significantly effective on viable cell numbers and 1-kestose (GF₂) concentrations. Contour plots were generated using a graphing software package (Surfer Mapping System, Version 5.0; Golden Software Inc., Golden, CO, USA, 1994) based on fitted quadratic regression equations. Optimum conditions for the highest viable cell number and higher GF₂ concentration were found to be around 35 °C fermentation temperature, 1.2% inoculum level and 25.0% peeled-fruit-to-water ratio for Ca-alginate immobilised cell fermentation, and around 39 °C fermentation temperature, 1.8% inoculum level and 25.0% peeled-fruit-to-water ratio for κ-carrageenan immobilised cell fermentation. For free cell fermentation, conditions for the highest viable cell number and higher GF₂ concentration could not be obtained. The predicted optimum conditions of immobilised cell fermentation and the experimental values were consistent. This verified the adequacy of these predicted models. It was concluded that RSM was appropriate for the optimisation of banana puree fermentation using cell immobilised L. acidophilus , and products with better synbiotic effects could be obtained. The consumer palatability of the immobilised cell-fermented banana puree was found to be acceptable.