啤酒酿造过程中铁离子的来源，变化及其对啤酒质量的影响

研究了啤酒酿造水、原料、添加剂及助剂中的铁含量和铁离子在啤酒酿造过程中的变化规律。原辅料及添加剂中均含有不同浓度的铁,硅藻土含铁量最高,大米最低。麦汁中铁离子浓度均值在0．29mg／L,发酵过程中部分被酵母吸收,大部分随沉淀物排出罐外。成品酒中的铁离子会促进啤酒羰基类化合物的生成从而影响啤酒风味质量,游离态铁离子会使啤酒货架期前期浊度值升高,而对啤酒色度无显著影响。     

铁离子与啤酒喷涌

啤酒喷涌产生的原因很多,有原料霉变引起的,也有其它因素引起的。随着制麦工艺和管理水平的不断提高,原料霉变引起的喷涌大为减少,但喷涌现象仍时有发生。主要原因是我国大多数中小型企业尚使用碳钢设备,不注意防腐,酒中铁离子超标,引起喷涌。本文主要探讨铁离子与啤酒喷涌的关系,及如何预防啤酒喷涌提出解决办法。     

啤酒中的铁离子

铁离子可促进酵母生长发育;又可引起啤酒混浊、产生金属味,降低啤酒质量.啤酒中的铁离子主要来源于原辅材料、设备管件及酿造用水等.铁离子在酿造过程易发生氧化还原、催化和络合反应,对麦汁糖化、发酵及成品啤酒质量产生影响.控制铁离子含量的方法有:控制原辅料及所用水的铁离子含量;适当提高糖化醪液的pH值;选用优良、强壮的酵母种;选用含铁较少的硅藻土助滤剂;选用耐酸不锈钢容器和管道,并作好防腐措施.(孙悟)     

铁离子在啤酒生产中的作用及控制

铁离子是对啤酒生产影响较大的无机离子之一,本文对铁离子在啤酒生产中的作用进行了阐述,并通过检测数据的分析,对其浓度变化趋势和控制手段进行了探讨。     

氧对啤酒质量的影响及消除方法

啤酒是一种组分复杂的胶体溶液，许多成分极易与氧反应生成其它物质，啤酒生产过程中，自始自终都存在氧的影响，只有根据不同的生产阶段，采取不同的方法措施才能消除氧的危害。     

硅藻土对啤酒中铁离子含量及啤酒质量的影响

目前世界上使用的啤酒助滤剂中，硅藻土占75％～80％。硅藻土中含有可溶性铁，过滤时进入啤酒，铁离子含量过高，对啤酒质量有不利影响。如：易引起铁蛋白混浊、引发啤酒的喷涌病、带给啤酒金属腥味等等。本实验的目的在于，通过检测不同品牌硅藻土的可溶性铁含量，处理后滤发酵液中铁离子含量，结合TBA实验，来评估不同品牌硅藻土对啤酒中铁离子含量及啤酒质量的影响。     

发酵果汁啤酒质量影响因素研究

研究以果汁为原料之一 ,以啤酒酵母为菌种 ,通过低温发酵制作果汁啤酒。从质量影响因素出发进行研究表明 ,麦芽汁 :果汁以 6∶1混合发酵较好 ,最终产品酒精度 3% (V/V) ,糖度 5 5°Bx,pH值 4 4,可获得令人满意的口感     

啤酒贮存期间pH对风味老化的影响

通过设计一个模型试验,快速调整、降低啤酒的 pH 值,然后分析其在贮存期间化学萤光产物的升高,异律草酮和原花色素的降解。通过感官测试表明:添加 HCl 到新鲜的啤酒中,在贮存期间会加快啤酒风味老化;但是,添加 HCl 到贮存过的啤酒中,啤酒风味老化现象并没有明显加快。因此,可以认为:啤酒风味老化的加快,并不完全取决于啤酒 pH 值的降低。在降低 pH 值条件下,醛类物质从老化风味——醛类氧化物中解离出来。基于这样一个事实,说明降低啤酒 pH值,在啤酒贮存期间,加快了风味老化反应、自由基反应。     

减少啤酒中铁离子含量的几条措施

铁离子能够促进啤酒沉淀物的形成 ,加速啤酒老化现象的产生 ;铁离子与自由基的产生有直接的关系。因此 ,在啤酒中应降低铁离子的含量 ,以降低其对啤酒质量造成的影响。     

INFLUENCE OF pH ON FLAVOUR STALING DURING BEER STORAGE

A decreasing pH accelerated an increase in the chemiluminescence production and degradation of isohumulones and procyanidins during the storage of beer and using a model system. The sensory test showed that the addition of HCI to fresh beer accelerated the flavour staling during beer storage but that the addition of HCI to stored beer did not significantly accelerate the flavour staling. Therefore, it was thought that the acceleration of beer flavour staling is not dependent on a decrease in pH such that the decreasing pH isolates stale flavour aldehydes by a dissociation from staling-flavour aldehyde adducts but based on the fact that the decreasing pH accelerates the flavour staling reactions, free radical reactions, during beer storage.     

THE DETERMINATION OF IRON COPPER AND CALCIUM IN BEER

The atomic absorption methods for iron, copper and calcium in beer, published by the American Society of Brewing Chemists, are recommended.     

CHARACTERISATION OF BEER PARTICLE CHARGES AND THE ROLE OF PARTICLE CHARGE IN BEER PROCESSING

Streaming current measurement has been shown to be an effective tool in measuring the net charge of beer particles. Using this method, it was demonstrated that non-microbiological particles of a number of beers could be either positively or negatively charged. Copper fining has been shown to significantly affect the net charge of the NMP in the resultant beer. Increasing the copper fining rate enhances the negative net charge of the NMP to a limiting value at which the addition of further copper finings has no effect. This is believed to correspond to the complete removal of all of the positively charged NMP by copper fining. The reduction in pH during fermentation results in the production of further positively charged NMP. The presence of positively charged NMP has been shown to have an adverse effect on isinglass fining performance. These results suggest that choice of raw materials and process conditions play as much of a role in defining fining performance as does careful consideration of fining rates .     

COLORIMETRIC DETERMINATION OF IRON IN BEER BY FLOW INJECTION ANALYSIS USING THE MERGING ZONES TECHNIQUE

A flow injection analysis system with colorimetric detection for the iron determination in beer is described. The methodology is based on the formation of a complex produced by the reaction of iron (II) with 1,10-phenanthroline, after reduction of iron (III) to iron (II) by ascorbic acid. The asymmetric merging zones technique was used to allow the sequential blank and sample absorbance readings. The results obtained with the developed system were in good agreement with those provided by the reference method (relative deviations lower than 4%) and exhibited a precision (relative standard deviation) better than 7%. A sampling-rate of 60 determinations per hour can be achieved.     

THE INSTITUTE OF BREWING ANALYSIS COMMITTEE DETERMINATION OF IRON AND COPPER IN BEER BY ATOMIC ABSORPTION SPECTROSCOPY

Methods for the determination of iron and copper in beer by atomic absorption spectroscopy are recommended on the basis of collaborative studies. The methods have better reproducibilities than the colorimetric methods currently recommended.     

THE INSTITUTE OF BREWING ANALYSIS COMMITTEE DETERMINATION OF IRON IN BEER

The method recommended for the determination of iron in beer utilizes a technique devised by the Alfred Jorgensen Laboratory. After reduction to the divalent state, iron is estimated spectrophotometrically as the coloured complex with 2,2′-dipyridyl, the absorbance of the final solution being measured at 528 mμ.     

THE ROLE OF ACTIVE AND INACTIVATED PAPAIN IN BEER CHILLPROOFING

The mechanism of chillproofing of beer by papain has been studied in a series of three experiments. Changes in the molecular size of proteins and polypeptides have been monitored by chromatographic profiles on Sephadex G-25 columns. Simultaneously the production of free amino acids and changes in the colloidal stability of the beer were determined. The addition of active papain to beer affected all three parameters. By contrast when inactivated papain was added to beer neither the chromatographic profile nor the concentration of free amino acids were altered but an increase in colloidal stability occurred. The removal of active papain from beer did not affect its colloidal stability but the removal of inactivated papain from beer stabilised with this agent eliminated the chillproofing effect.     

EFFECT OF CALCIUM IONS IN SORGHUM BEER MASHING

One of the problems in sorghum beer brewing is that of sugar production. This is because sorghum malts are low in diastatic activity, the grist contains a high proportion of adjunct and in some brewing processes conversion is carried out at pH 4. Since the positive effects of calcium ions on alpha-amylase activity are well described, the use of additional calcium in sorghum mashing was investigated. Mashing at pH 4.5 in the presence of 0.1% calcium acetate (227 ppm Ca) resulted in almost complete conservation of diastatic activity during conversion and higher reducing sugar production compared with tap water (31 ppm Ca). At a mash pH of 4, a calcium ion concentration of approximately 200 ppm gave maximum reducing sugar production and wort yield and increased extract. Under these conditions, some alpha-amylase activity was detected at the end of the conversion, whereas without calcium no alpha-amylase activity was detected. It, therefore, appears that improved conversion took place due to the conservation of alpha-amylase activity by calcium ions. The inclusion of additional calcium ions in sorghum beer mashes also enabled the same amount of sugar production compared with straight tap water but using a substantially lower proportion of malt in the grist.     

三种黄酮类化合物抗自由基的研究

通过连苯三酚法测定金银花和葛根超声波提取液清除超氧自由基的能力。结果表明：金银花和葛根提取液其清除超氧自由基的能力与作用时间成反比,抗超氧自由基的能力与提取液浓度成正比。通过DPPH法测定金银花、葛根和栗子叶提取液清除自由基的能力。结果表明：它们清除能力与提取液浓度成正比,提取液清除自由基的能力为：金银花〉葛根〉栗子叶。     

蜂胶抗氧化作用研究

研究蜂胶清除自由基和抗油脂氧化作用的能力。结果表明，蜂胶提取液清除·OH自由基的能力与总黄酮含量呈正相关；蜂胶具有良好的抗油脂氧化能力，其能力略高于同浓度的二丁基羟基甲苯（BHT）。