The Dynamic Changes of Proton Efflux Rate in Saccharomyces pastorianus Strains During High Gravity or Very High Gravity Brewing

The changes in the proton efflux rate (PER) during fermentation of normal gravity (NG), high gravity (HG) and very high gravity (VHG) wort by a lager yeast (Saccharomyces pastorianus) were monitored using an optimized PER test method. The values of the proton efflux rate in S. pastorianus decreased with increasing initial wort gravity. Moreover, the difference in the proton efflux rate values at the beginning of the fermentation was lower than at the end of fermentation from normal gravity to very high gravity brewing. These results demonstrated that the proton efflux rate in S. pastorianus was inhibited in the later stages of high gravity and very high gravity brewing. Furthermore, the changes of the proton efflux rate in S. pastorianus under the high ethanol concentration conditions appeared to depend on the concentration of ethanol in the fermentation liquid. A better negative correlation (P > 0.001, r = ?0.95) between the ethanol concentration at >4% (w/v) and the proton efflux rate was found. The changes of the proton efflux rate in the cells treated with exogenous ethanol confirmed that higher concentrations of ethanol could significantly inhibit proton efflux in S. pastorianus. This study offers a possible way to monitor and explain the performance of yeast in the complex environment of high gravity and very high gravity brewing.     

The Effect of Pitching Rate on Fermentation and Flavour Compounds in High Gravity Brewing

The effect of pitching rate on fermentation and production of flavour compounds was studied in high gravity wort using a lager yeast. Fermentation performance was followed by monitoring the total sugar content and yeast growth. Volatile compounds were evaluated by analysing higher alcohols, esters and carbonyl compounds at the end of fermentation. Faster fermentation rates and higher yeast counts were observed with the higher pitching levels. Lower amounts of 2‐ and 3‐methyl‐1‐butanols and higher levels of 2‐methyl‐1‐propanol were found at the increased pitching rates. The concentration of isoamyl acetate was reduced with an increased pitching rate. Higher amounts of diacetyl and 2,3‐pentanedione were obtained at the lower pitching levels.     

啤酒高浓酿造的研究

探讨了高麦汁浓度对酵母生长发酵的影响 ,研究了麦汁溶氧对酵母生长发酵的促进作用。实验结果表明 :随着麦汁浓度的增加 ,酵母糖降速率明显降低 ;相同浓度的麦汁 ,α 氨基酸含量低 ,酵母糖降速率下降 ;α 氨基氮含量高 ,酵母增殖密度明显增加 ,但单位α 氨基氮生成酵母细胞干重降低 ,即增加的α 氨基氮未被充分用于生成酵母细胞 ;充入纯氧能显著提高麦汁的饱和溶氧量 ,采用二次充氧比一次充氧能够显著提高啤酒发酵度 ,并缩短发酵时间     

高浓酿造技术研究进展

高浓酿造技术的主要优点通过有效降低糖化的用水，仅利用现有糖化、发酵和储存设备即可大幅度提高啤酒产量，缺点包括：降低糖化锅原料及煮锅酒花利用率，泡沫稳定性下降，酸洗效应，降低酵母存活率，酵母回用代数下降以及需要及时调整麦汁中二阶离子的浓度。     

高浓酿造过程中几个技术问题探讨

高浓酿造具有降低生产成本、突出啤酒淡爽风格等优点。本文对原料选择、粉碎方法、辅料等技术问题进行了分析了和探讨。     

Characteristics of High Cell Density Fermentations with Different Lager Yeast Strains

To improve the productivity of the beer fermentation process, several strategies can be adopted. One of these promising strategies could be the increase of suspended yeast cells in the reactor. Therefore, the fermentation characteristics of 11 lager yeast strains were studied in normal pitched worts (20 × 10⁶ cells/ mL) (LD) and in worts with a four‐fold higher pitching rate (HD). The fermentation rate was 2–4 times increased when high initial cell levels were used. The net yeast growth was somewhat similar between the LD and the HD fermentations, although the FAN uptake level was about 35% higher in the HD fermentations compared with LD. High viabilities were observed throughout the fermentations with high cell loadings. HD fermentations resulted in higher concentrations of all the measured fusel alcohols and higher maxima and residual concentrations of total diacetyl were observed. In contrast, higher levels of most of the esters were found at the normal pitching rate, although the results of isoamyl acetate were not significant. With the help of “Principal Component Analysis”, it became clear that the cell density had an important influence on the flavour profile, but that yeast specific preferences could not be overlooked as they determined the sensitivity of the yeast to the application of higher cell densities.     

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.     

高浓酿造技术在啤酒工业中的应用

高浓酿造技术在啤酒工业中的应用越来越广泛，其主要特点是在不增加设备的基础上能大幅度提高产量，对高浓酿造技术在啤酒工业中的应用进行了较为详细的论述，总结了高浓酿造的特点、高浓麦汁的制备、啤酒酿造糖浆的选择等。最后，讨论了高浓酿造技术对酿造工艺过程、啤酒酵母及最终产品的影响。     

高浓酿造与啤酒风味协调柔和性

本文主要介绍了啤酒风味物质、风味类型，在此基础上对当前啤酒界普遍采用的高浓酿造技术进行了总结和阐述，并分析了此工艺对啤酒风味物质组成及感官品评特性的影响。     

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.     

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.     

酿造单宁在啤酒高浓酿造中应用效果的评价及其影响因素的探讨

将酿造单宁应用于高浓酿造啤酒生产中,研究发现,酿造单宁能明显提高啤酒质量,改善啤酒风味,提高其稳定性和抗老化能力,延长保鲜期,缩短生产周期,改善成品啤酒的感官特征等。应用酿造单宁后,啤酒中的总多酚含量变化不大,经风味评价,啤酒的主要风味物质无明显变化。啤酒中Ca2+含量在适宜范围内(30～85mg/L),酿造单宁不会对啤酒酿造产生影响;但若Ca2+含量超出合理范围,则会对啤酒的浊度产生一定的影响。异α-酸含量在一定范围内,尚未发现对酿造单宁应用效果产生影响。     

酿造水对低度啤酒质量的影响——诠释红石梁的酿造用水

近来低浓度啤酒在中国较受欢迎,尤其在南方地区更为突出。但是随着原麦汁浓度的降低,啤酒的各种异杂味易露头,因此酿造用水的质量对低度啤酒的口感起着非常重要的作用。通过对酿造水的改良,可以解决低度啤酒质量中遇到的口感酸涩、非生物稳定性差等一些技术难题,提高啤酒质量。     

啤酒高浓酿造中氨基酸对酵母发酵性能和啤酒色值的影响

探讨在24?°P高浓啤酒发酵过程中8?种氨基酸（Met、Phe、Trp、Arg、His、Ile、Leu、Lys）的不同添加量（分别为原麦汁中相应氨基酸含量的0.5、1?倍和2?倍）对酵母生理特性、发酵性能和啤酒色值的影响。结果表明：8?种氨基酸的补充可显著提高麦汁发酵度、乙醇产量,促进酵母生长,提高酵母活细胞率,改善啤酒色值。其中,补充1?倍氨基酸的高浓麦汁发酵性能较好,与对照组相比,发酵度、乙醇产量、最大悬浮酵母细胞数和发酵结束时的酵母活细胞率分别提高了6%、17%、11%和10%。添加氨基酸的高浓酿造啤酒经稀释后,啤酒色泽依然鲜亮,且添加1?倍氨基酸酿造而成的啤酒经稀释后色差（ΔE）最小,色泽最接近青岛纯生啤酒。     

浅色焦香麦芽在低度淡爽型啤酒酿造中的应用

浅色焦香麦芽含有较多的类黑素等高分子物质，研究采用添加6％的浅色焦香麦芽酿造低度淡爽型啤酒。结果表明，添加浅色焦香麦芽可使啤酒口味更加柔和醇厚；明显增加麦芽香味；不影响啤酒的色度；可增加啤酒的泡沫性；成熟啤酒的各项指标符合GB4928要求；该麦芽适合酿造低度淡爽型啤酒或酿制高辅料比啤酒。     

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。     

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。     

The Loss of Hydrophobic Polypeptides during Fermentation and Conditioning of High Gravity and Low Gravity Brewed Beer

The object of this study was to investigate the loss of hydrophobic polypeptides, which are important for foam quality and stability in finished beer. Loss of hydrophobic polypeptide due to fermenter foaming occurs during transfer of fermented wort since a gradient of hydrophobic polypeptides towards the surface is created during fermentation. Due to higher polyphenol levels in high gravity (20°Plato) wort, more hydrophobic polypeptides are lost due to cold break (cold trub) precipitation compared to low gravity (12°Plato) wort. Another important factor affecting the loss of hydrophobic polypeptides could be proteinase A activity during fermentation, especially in high gravity fermentation where the yeast is exposed the higher stress. During high gravity fermentation, where osmotic pressures are higher, ethanol levels become greater, and nitrogen‐carbohydrate ratios are lower, more proteinase A is released by the yeast. This release of proteinase A into fermenting wort could have implications for the foam stability of the finished product.     

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.     

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。