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.     

Elucidation of the Role of Nitrogenous Wort Components in Yeast Fermentation

The Free Amino Nitrogen (FAN) content of wort prescribes efficient yeast cell growth and fermentation performance. FAN consists of the individual amino acids, small peptides and ammonia ions formed during malting, the relative amounts of which vary. In this paper, the individual constituents of FAN were dissected and their effect on both ale and lager fermentations determined. The patterns of amino acid and small peptide uptake and the changes in extracellular protease activity revealed the dynamic environment that develops during fermentation. Lysine and methionine, previously identified as key amino acids in wort fermentation, were investigated further.     

Effects of Magnesium,Calcium and Wort Oxygenation on the Fermentative Performance of Ale and Lager Strains Fermenting Normal and High Gravity Worts*

The effects of increased magnesium and calcium concentrations in oxygenated and non-oxygenated conventional and high gravity worts under static conditions were investigated. The addition of 500 Mg²⁺ to the oxygenated 1048 OG and 1080 OG worts resulted in the most favourable changes to key fermentation parameters leading to increased ethanol production, enhanced vitality, increased cell numbers and an initial increased rate of fermentation, by an ale and lager yeast strain. Elevated Mg²⁺ levels in the non-oxygenated worts led to increased ethanol production, enhanced vitality and increased cell numbers but to a lesser degree when compared with the oxygenated worts. The addition of 800 ppm Ca²⁺ resulted in decreased fermentation rates, reduced ethanol production, decreased vitality and lowered cell numbers by both the ale and lager strain, in both the conventional and high gravity worts. The detrimental effect of added Ca²⁺ was exacerbated in the non-oxygenated worts.     

The Yeast Vacuole ‐A Scanning Electron Microscopy Study During High Gravity Wort Fermentations

The yeast vacuole has been shown to exhibit morphological responses to environmental conditions when exposed to worts of different gravity during fermentation. Marked effects of high gravity wort (20° Plato) on yeast morphology compared to more conventional wort gravity (12° Plato) were observed. High gravity worts caused vacuolar enlargement compared to conventional gravity wort. These results suggested that yeast cells experienced severe alterations with the vacuolar tonoplast when exposed to high osmotic pressure and elevated levels of ethanol.     

125th Anniversary Review: Yeast Flocculation and Sedimentation in Brewing

Flocculation is prerequisite for bulk sedimentation of yeast during brewery fermentation. Although single yeast cells gradually sediment in green beer, this sedimentation rate is too slow without formation of large yeast flocs. The present review concerns the major determinants of yeast flocculation and sedimentation in brewery fermentations. Flocculation characteristics of yeast are strongly strain‐dependent and largely defined by which FLO genes are functional in each strain. In addition to the genetic background, several environmental factors affect flocculation. These can be, somewhat arbitrarily, classified as physiological factors, such as the calcium availability, pH, temperature and ethanol and oxygen concentrations in the medium or physical factors, such as cell surface hydrophobicity, cell surface charge and the presence of appropriate hydrodynamic conditions for the formation of large flocs. Once yeast flocs are formed, their size, shape and density and the properties of the surrounding medium affect the rate at which the flocs sediment. Higher gravity worts usually result in green beers with higher viscosity and density, which both retard sedimentation. Moreover, environmental factors during yeast handling before fermentation, e.g., propagation, storage and cropping, influence the flocculation potential of yeast in subsequent fermentation. Premature yeast flocculation (PYF) and the role of PYF factors are discussed. In conclusion, some potential options available to adjust yeast flocculation are described.     

125th Anniversary Review: Diacetyl and its control during brewery fermentation

Diacetyl is a butter‐tasting vicinal diketone produced as a by‐product of yeast valine metabolism during fermentation. Concentration is dependent on a number of factors including rate of formation of the precursor α‐acetolactate by yeast, spontaneous decarboxylation of this acetohydroxy acid to diacetyl and removal of diacetyl by yeast via the action of various reductase enzymes. Lowering concentrations of diacetyl in green beer represents an expensive and time‐consuming part of the brewing process and strategies to minimize diacetyl formation or hasten its reduction have potential for improving overall efficiency of the lager brewing system. Here we review the processes that determine diacetyl levels in green beer as well as the various ways in which diacetyl levels can be controlled. The amount of diacetyl produced during fermentation can be affected by modifying process conditions, wort composition or fermentation technique, or by yeast strain development through genetic engineering or adaptive evolution. The process of diacetyl reduction by yeast is not as well understood as the process of formation, but is dependent on factors such as physiological condition, cell membrane composition, temperature and pH. The process of diacetyl removal is typically rate‐limited by the reaction rate for the spontaneous decarboxylation of α‐acetolactate to diacetyl. Copyright © 2013 The Institute of Brewing & Distilling     

安琪超级酿酒干酵母在酒精浓醪发酵中的应用

采用安琪超级酿酒干酵母，以玉米、木薯为原料的酒精浓醪发酵，最佳工艺条件为：①液化条件：耐高温α-淀粉酶10～20μ／g，60～70℃润料30min，90～95℃液化90min；②糖化条件：糖化酶100～200u／g，无糖化；③pH：4．0～5．0；④发酵温度：30～35℃；⑤酵母接种量：实验室小试接种量为原料的0．2％，中试接种量0．05％～0．1％，大生产接种量在0．02％～0．05％。采用双酶法连续发酵工艺，要求原料粉碎细，料水比适当（1：2．3～2．5）。（小凡）     

Acid Washing and Serial Repitching a Brewing Ale Strain of Saccharomyces cerevisiae in High Gravity Wort and the Role of Wort Oxygenation Conditions†

Acid washing pitching yeast is an effective method for removing bacterial contamination, but if the yeast is washed incorrectly decreased fermentation performance and beer quality problems may result. Various factors can affect the acid resistance of yeast strains during brewery fermentations. Yeast from shaking flask experiments was more resistant to the combination of high gravity and acid washing conditions than yeast cropped from static fermentations. Yeast harvested from static high gravity wort (20° Plato; 1.083 OG) fermentations was more adversely affected by acid washing than yeast from standard gravity (12° Plato; 1.048 OG) wort. Wort oxygenation resulted in enhanced yeast fermentation performance and healthier yeast crops when yeast was serially repitched into 20° Plato wort. Yeast cropped from fermentations with air saturated high gravity wort responded poorly when acid washed. These results suggest that the structure of the plasma membrane particularly the sterol and fatty acid composition, may have an important role in tolerating high gravity wort and acid washing conditions.     

Yeast Proteolytic Activity During High and Low Gravity Wort Fermentations and its Effect on Head Retention

The aim was to discover the effect of high gravity brewing on yeast protease activity during fermentation, on the loss of hydrophobic polypeptides from wort during fermentation, and on the foam stability of stored beer. The hydrophobic polypeptide content of low (10° Plato) gravity worts showed a steady decline throughout fermentation, but for the 20° Plato wort there was a rapid decline over the first 8 days of fermentation, followed by little change over the remaining period. The decrease in hydrophobic polypeptides was greater in the high gravity fermentation. Proteinase A increased during fermentations with the highest levels being present at the end of fermentations. High gravity fermentations exhibited levels of yeast protease that from the 3rd to 11th day of fermentation were at least twice the values of the low gravity fermentations. The high gravity brewed beer contained significantly higher levels of proteinase A activity than the low gravity brewed beer. The inclusion of FERMCAP™, an antifoam, in high gravity wort did not affect either the hydrophobic polypeptide levels or foam stability of the resultant beer. This suggests that proteinase A, rather than fermenter foaming, must be the major contributor to the lack of foam stability of high gravity brewed beer. Head retention measurements conducted on the high and low gravity brewed bottled beers, over a five month period, demonstrated a steady decline in foam stability for both beers. The declines in head retention did not occur in high and low gravity beers that had been pasteurised.     

The Combined Effects of Oxygen Supply Strategy,Inoculum Size and Temperature Profile on Very‐High‐Gravity Beer Fermentation by Saccharomyces cerevisiae

The timing and concentration of oxygen supply to wort are of particular relevance in industrial beer brewing where tank volumes exceed brewhouse capacity, thereby necessitating fermenter filling in a multiple‐brew fashion. A simple technique for accurately controlling dissolved oxygen concentration is presented to model industrial, multi‐brew fermentations at bench and pilot scales. This method was employed to identify an effective oxygen supply strategy for batch fermentations conducted with very‐high‐gravity (VHG) wort. Addition of 25 ppm dissolved oxygen to the fermenting wort, 12 h after inoculation, was the most effective oxygenation strategy and reduced fermentation time by 33% compared to the control conditions. Pilot‐scale trials were subsequently conducted to further optimize VHG batch fermentation performance through simultaneous manipulation of key fermentation process parameters, including increased yeast inoculum size, early and increased free‐rise timing and temperature, and optimized oxygenation strategy. This approach reduced the time to achieve end of fermentation targets by 34% compared to trials conducted under control conditions. The improved fermentation profile was consistent over three successive inoculations and minimal impact was observed on key flavour volatiles. Employing the optimized process for VHG batch beer production would be industrially desirable due to the potential for improved process efficiency and cost‐savings.     

Wort composition and its impact on the flavour‐active higher alcohol and ester formation of beer – a review

The most significant factors influencing beer quality are the variety of aroma flavours that stem from a complex system of interactions between many hundreds of compounds. With increasing demand for flavour control and enhanced productivity, the presence of consistent and balanced amounts of higher alcohols and esters are critical aspects of process control. Extensive research has focused on the formation of flavour compounds by the brewing yeast and the factors that influence their synthesis. Fermenting wort is a complex medium from which the brewing yeast utilizes nutrients for living and growth and to where it places its metabolic by‐products. Thus, changes in wort composition will greatly influence final beer aroma. The current paper reviews up‐to‐date knowledge on the contribution of wort composition to the flavour quality of the final product, in particular higher alcohols and esters. Different wort constituents involved in the biosynthesis of these aromatic substances, and which therefore require control during brewery fermentations, are reviewed. Copyright © 2014 The Institute of Brewing & Distilling     

酵母菌株对低浓度啤酒酿造的影响

啤酒酵母BY - 1,BY - 2 ,BY - 3和BY - 4分别接入 6°P、7°P、8°P麦汁中 ,10℃发酵。监控发酵过程中的酸度、pH值、酒精度 ,并对过滤啤酒进行感官品评。相同麦汁浓度下 ,4株酵母的发酵液酸度、pH、酒精度值无较大差异。发酵后 6°P麦汁pH值下降约 1.5 ,7°P、8°P麦汁下降约 1.2。发酵 6°P、7°P和 8°P麦汁时 ,BY - 2酵母所酿啤酒风味最佳。     

125th Anniversary Review: The importance of learning

Learning has been at the heart of mankind's advances from ‘hunter gatherer’ to ‘organized’ and continues to be at the core of the development of our civilization. Learning takes many forms – we can learn by observation and by demonstration and we can learn from outcomes and from deliberate experimentation. Acquired knowledge is preserved and new knowledge added ‘to the bank’ through the written word and through the wisdom of individuals. Knowledge underpins how and why we do things and forms the basis of developing new ideas. If knowledge is not shared and then acquired by individuals, then those individuals will be at a competitive disadvantage to their peers. Organizations that develop and nurture their knowledge pool will demonstrate superior performance and engender a more innovative and dynamic working environment. Copyright © 2012 The Institute of Brewing & Distilling     

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。     

玉米原料超高浓度酒精发酵

以全磨玉米为原料,研究了超高浓度条件下传统工艺与生料工艺的黏度变化。采用传统工艺,在超高浓度条件下,物料的糊化、液化会变得非常困难。而采用生料工艺,黏度始终维持在合理的水平。对高浓度传统工艺和生料工艺发酵的结果进行对比,证明生料工艺可以产出更多的酒精;对超高底物浓度(35%绝对干物)生料发酵时采用温度梯度控制,使用市售酒精干酵母,在98 h内发酵醪液酒精浓度可达20%以上。     

125th Anniversary Review: Water sources and treatment in brewing

At one time the raw water naturally available influenced the development of typical regional beer styles. With the development of reliable and efficient water treatment technologies, breweries became independent of the local raw water quality. The proliferation of large breweries is still closely linked to progress in water treatment. The prevailing question is always how to best condition the raw water for the different purposes within the brewery in the most efficient way. The raw water starting points are very different and can range from well water, to surface water, to municipal water, and in some cases to more exotic water sources such as rain or even treated wastewater. The impact of different water ions on the brewing process is discussed, with a special focus on technological requirements, as well as microbiology and corrosion issues. The requirements of divergent water types commonly used for brewing, dilution, service and boiler feed water, and available treatment steps based on examples of large‐sized plants are discussed, including traditional methods such as lime softening and ion exchange, as well as more recent treatment systems. Membrane technology is highlighted, as it has had a great impact on treatment technology. Following the success story of reverse osmosis, and more recently developed ultrafiltration, there is now more focus on special applications such as the substitution of lime saturators to produce clear lime water with membranes. This requires higher performance and robustness of the membranes. Finally, some future challenges for water treatment in breweries are outlined. Copyright © 2012 The Institute of Brewing & Distilling     

同步糖化浓醪发酵影响因素的探析

目前发酵法生产燃料乙醇普遍存在着成本较高,耗能过大的问题,解决这些问题已成为今后发酵法生产技术的发展方向。高浓度酒精发酵为生产企业提高经济效益,节约能源,保护环境起到积极的促进作用,在浓醪发酵工艺基础上,采取同步糖化工艺措施能够进一步降低原料消耗及综合能耗,符合燃料乙醇生产技术发展方向,具有重要的推广价值。充分探讨同步糖化发酵过程的影响因素,在工业装置上摸索出同步糖化浓醪发酵过程的控制手段,在传统发酵酒精浓度12％vol的基础上,发酵酒精浓度增加到14％vol。     

125th Anniversary Review: The Role of Hops in Brewing

Although hop technology has been a substantial part of brewing science for the last 130 years, we are still far from claiming to know everything about hops. As hops are considered primarily as a flavour ingredient for beer, with the added benefit of having anti‐microbial effects, hop research is focused on hops as a bittering agent, as an aroma contributor and as a preservative. Newer fields in hop research are directed toward the relevance of hops in flavour stability, brewing process utilisation, the technological benefits of hops in brewing as well as hops as a source of various substances with many health benefits. However the more we find out about the so‐called “spirit of beer” the more questions emerge that demand answers. While hop research was only an ancillary research field for decades, during the last ten years more universities and breweries have determined that hops must play a meaningful role in their research efforts. This article gives an overview of the up‐to‐date knowledge on hop aroma, hop derived bitterness, and the role of hops in flavour stability as well as light stability. Hop research is a wide field, therefore in this review only selected topics are reviewed. Other research areas such as hops utilisation, the antifoam potential of hops, or the advances in knowledge pertaining to the physiological valuable substances of hops go beyond the scope of this article.     

125th Anniversary Review: Advances in analytical methodology in brewing

Comprehensive sets of chemical, microbiological and sensory methods have long been available to characterize individual beers and explore the relationships between raw materials, process conditions and the outcome of the brewing process. Although the majority of major brewers are increasingly using quality assurance as opposed to quality control as the basis of operation, the need to use chemical analyses is still perceived as an essential prerequisite to brewing. The requirement to meet the various legislative codes and the need to manage the consistency of international brands arising from several individual breweries make the possession of robust analytical procedures essential. In many breweries there is a trend towards devolving traditional analytical tasks from central quality control laboratories manned by dedicated technicians to satellite stations, where the analyses needed to support production are performed directly by process workers. Parallel to these changes is a desire to achieve a greater understanding of the complex relationships between beer analysis and overall quality, in particular, the identification of markers that allow for the identification of processes such as beer ageing. This review summarizes the ways in which brewing analytical methods and the suppliers of analytical apparatus are evolving to meet the needs of the current modern industry. Copyright © 2012 The Institute of Brewing & Distilling