The Economic importance of yeast rem Gaye Kars

The Economic importance of yeast İrem Gaye Kars Lider Serçemeli

Objectives To appreciate that some microorganisms are useful to humans To recall an equation for anerobic respiration To understand the industrial production of alcohol and bread

Let’s learn bread production FİRST STEP Flour , sugar , water and salt are mixed with yeast. This process is called kneading and produces dough.

SECOND STEP The dough is rolled into shape , then kept in a warm (about 28 C) , moist enviroment. The yeast ferments the sugar , and the bubbles of carbondioxide are trapped by the sticky proteins of the dough. The dough expands or rises.

THİRD STEP Cooking at 180 celcius – baking : Kills the yeast and stops fermentation Causes alcohol to evaporate Hardes the outher surface to form a crust.

FİNAL STEP The product is bread , which should be : o Spongy in texture , because of trapped carbon dioxide. o Fresh smelling (partly alcohol vapour !). v

Yeast performs alcoholic fermentation Much of commercial use of microorganisms is based on the process of fermentation. This term covers any metaabolic process carried out by microorganisims using carbonhydrate as starting material. The bestknown fermentation reaction is anaerobic respiration of glucose by single-celled fungus yeast :

Glucose Carbon dioxide + ethanol + energy Since one of the products is ethanol this process is often known as alcoholic fermentation. As well as making alcohol , the carbon dioxide produced is valuable commercially. For the yeast , the useful product is energy – the alcohol and carbon dioxide are by – products.

Alcoholhas a high energy content and is toxic Alcohol contains a great deal of energy , a fact that is exploited when alcohol is used as a fuel source. Alcohol is also toxic (poisonous) and the yeast excretes it into the surroundings liquid medium. If the alcohol concentration in the medium gets higher then 8 -9% , the yeast is killed and fermentation stops.

Fine turning the fermentation process Because of the enormous commercial significance of these processes much research has gone into making them as efficent as possible. For example : Strains of yeast that are tolerant to higher concentrations of alcohol have been developed High-yielding strains of barley have been selectively bred. Genetic engineers have developed yeasts which can cover starch to maltose, and thus remove the need for the malting stages.