5.5 understand the role of yeast in the production of beer

5.5 •yeast is used for brewing beer

                •1. get the sugar out of the grain 

                •2. yeast is added to the mixture and is incubated

                          •the yeast ferments the sugar into alcohol, to stop unwanted microorganisms and air getting in

                          •the rising concentration of alcohol (ethanol) is due to anaerobic respiration, eventually starts to kill the yeast - as it dies fermentation slows down

                                    •different species of yeast can tolerate different levels of alcohol 

                •3. clarifying agents are added to remove particles 

                •4. the beer is pasteurised - to kill any yeast left and stop fermentation 

                •yeast has: chitin cell walls, mitochondria, cytoplasm, cell membrane and nucleus 

                •feeds by saprotrophic nutrition and reproduces by mitosis (single-celled) 

                •glucose —> ethanol + carbon dioxide - ethanol is the alcohol  

                •C6H12O6 —> 2C2H5OH + 2CO2 (yeast is a catalyst)