Aeration and Fermentation

Brewing is a fermentative process which converts carbohydrate rich raw materials into beer using yeast catalysts such as Baker’s yeast and species of Saccharomyces. Water quality and aeration conditions influence beer quality to a greater extent. Of these two, aeration plays a vital role. Aeration and Fermentation: Studies revealed that yeast cells propagation was doubled when cultured under prolonged aerobic conditions as compared to discontinuous aeration. Moreover, increase in cell growth was proportional to aeration volume, mainly due to the synthesis of sterols and unsaturated fatty acids which are important elements of the yeast cell membrane. Under batch fermentation, aeration affected 1st fermentation; nevertheless, successive fermentation was yeast strain dependent. Chul (2002) observed significant differences in levels of aroma compounds obtained with yeast propagated under different aerobic conditions. However aerobic conditions were not found to affect the levels of diacetyl.   According to Chul et al (2007), continuous aeration during yeast propagation directly influenced yeast metabolism, fermentation ability and beer quality. Microbial contamination risks: Certain groups of micro-organisms pose contamination risk in brewing. Most hazardous beer spoilage microbial agents are the species of Lactobacilli, Pedicocci and Micrococcus kristinae. Lactobacilli are gram-positive, facultative, anaerobic bacteria. Some species of Lactobacilli which are the common beer spoilage organisms are said to operate using homofermentative metabolism, by lowering the pH of fermentation process by producing lactic acid. These species are generally resistant to hop compounds. Lactobacillus brevis has the ability to ferment dextrins and starch and its contaminations in beer cause turbidity and super-attenuation (Vaughan et al. 2005). Pediococci are also homofermentative bacteria, which normally grow in pairs or tetrads, and are found in finished beers and wort fermentations. Presence of Pediococci leaves behind fermentable sugars in beer even after fermentation, thus causing ropiness. Micrococcus kristinae is an aerobic, gram-positive coccus occurring in tetrads or groups of four, forming pale cream to pale orange colonies. The primary habitat is the mammalian skin (Microbial glossary). Most of the strains are non-pathogens but some tend to be opportunistic pathogens. These species can grow in beer with significantly lower levels of alcohol and hop compounds and at pH values above 4.5 (Vaughan et al. 2005) and produce a fruity atypical aroma. Gram negative anaerobic bacteria such as Pectinatus cerevisiiphilus, Pectinatus frisingensis, Selenomonas lacticifex, Zymophilus raffinosivorans and Zymomonas mobilis are also potential beer spoilage microbes. Pectinatus species have found to greatly affect non-pasteurized beers rather than pasteurized ones. These anaerobic organisms ideally grow in packaged products between 15 and 40 °C with an optimum at 32 °C and at a pH of 4.5 (Vaughan et al. 2005). They are found to produce significant amounts of acetic acid, propionic acid and acetoin in wort and packaged beers. They also produce hydrogen sulphide and methyl mercaptan and cause considerable turbidity and an unpleasant ‘rotten egg’ odor in beer. Zymomonas mobilis is an organism widely used in the bio-ethanol synthesis. However, this species contaminates beer when it produces significantly higher levels of acetaldehyde and hydrogen sulphide. Gram negative aerobic bacteria such as Hafnia protea and Enterobacter cloacae also other agents which cause beer spoilage and are capable of surviving beer fermentation. Certain species of Saccharomyces are also organism causing beer contamination. Works Cited: Cheong, Chul.   Wackerbauer, Karl. and Kang, Soon AH. â€Å"Influence of aeration during propagation of pitching yeast on fermentation and beer flavor.† J. Microbiol. Biotechnol. 17(2). 2007: 297 – 304. Microbial glossary – Environmental Diagnostic Laborarory, retrieved from http://www.pureaircontrols.com/glossary.html Vaughan, Anne. O’Sullivan, Tadhg.   and Sinderen, Douwe Van. â€Å"Enhancing the Microbiological Stability of Malt and Beer – A Review.† Publication no. G-2005-1316-408. The Institute of Brewing Distilling. 111 ( 4). 2005: 355 – 371.

Nanotechnology Annotated Bibliography Example | Topics and Well Written Essays - 1250 words

Nanotechnology - Annotated Bibliography Example The purpose of the site is to explain the basic concepts related to nanotechnology and refer to the latest news, events and articles. The author Earl Boysen was a co-author of the book Nanotechnology for Dummies (Richard Booker & Earl Boysen, Wiley Publishing). He started the website with view to explaining the concepts in book in simpler understandable format. I am recommending this site because the website contains excerpts from the book Nanotechnology for Dummies further explaining the concepts in detail. It is a good resource for gaining a basic understanding of the field and to remain in touch with the latest research activities. It provides links to resources and articles for further reading, lists the descriptions of jobs available in the field. It even provides a simple lesson plan for the students of middle and high schools. The purpose of the site is to host a complete book related to the basics of nanotechnology online. The author Drexler, K. Eric, Ph.D., is an active researcher and author of a number of conference and journal articles besides this book. His work mainly focuses on the advanced nanotechnologies and the directions of the current research. He also served as Chief Technical Consultant to the Technology Roadmap for Productive Nanosystems and is currently working with World Wildlife Fund exploring nanotechnology-based solutions to global problems such as energy and climate change. I am recommending this site because the entire book is available online in html format. The book covers the basic context, concept and possible applications of nanotechnology and therefore can be used as a good creative study reference guide. The purpose of the site is providing latest research and development news, articles, resources and a blog on nanotechnology and its applications as well as any raised issues. The publisher, Foresight Institute is a

Not deciding yet Essay Example | Topics and Well Written Essays - 500 words

Not deciding yet - Essay Example In other words, we can also say that the gradual increase in the minimum wage rate will show relatively negative values of the employment rate in the US labor market. The maximum wage rate will result into the highest negative value of the employment rate. These statistics are shown in the research study conducted by the Federal Department, which was conducted to check the implications of the proposal of increase in the minimum wage rate maximum up to $ 9 – 10 / hour. In case of a perfect competition in the market among different firms, all the resources are equally available to all the possible market players. The firms are facing a neck-to-neck competition between each other competitive firm. In this situation, every decision should be taken very carefully because the firm managers will have to compete with many other game players also. Therefore, according to my opinion an increase in the minimum wage rate in case of a perfect competitive market will cause a decrease in the employment rate of that particular labor market. Because if any State or Government is increasing the wage rates then firms or the employers still have other options available to hire the cheap labor from where it is available. In case of a monopolistic competition, all the firms have individual products and services; they are not competing directly with each other just because of the reason that their products are not exactly substitute to each other. In case of a monopoli stic competitive market, the increase the minimum wage rate may also cause an increase in the employment rate just because of the reason that every firm will require certain skills and expertise for their production. They cannot hire any available labor if they are cheap as compare to the home market. The products and services of the firms are not similar to each other therefore; there will be certain set of skills, which is required by any manager of the firm. Therefore, we can predict that in case of a