ABSTRACT
The effects of temperature on the growth of yeast and on its metabolic activity in distiller’s malt wort have been studied. In un-aerated fermentations, maximum yeast production takes place at about 30° C. whereas the growth rate in aerated cultures is highest at 35° C. The lag phase of the yeast studied fell from 6 hr. at 20° C. to 2-8 hr. at 25° C. and was not thereafter greatly affected by increases of temperature until 42° C. was reached, at which point growth ceased. Maltase activity was maximal at 25° C. when considered in terms of unit quantities of either yeast or fermenting wort, but the optimum temperature for initial fermentation velocity varied according to the time over which the measurement was made, being maximal at 40° C. for 0-5 hr., and at 35° C. for 2 hr. Alcohol production was highest at 25° C. whereas glycerol and higher alcohol formation took place optimally at 30° C.
CHAPTER ONE
1.0 Introduction
The word “Yeast” comes to us from the old English gist, gyst and from the indo-European root yes-meaning boil, from or bubble. Yeast microbes are probably one of the earliest domesticated organizing. People have used yeast for fermentation and baking throughout history. Archaeologists digging in Egyptian ruins found early grinding stones and baking chambers for yeasted bread, as well as drawings of 4,000. years- old bakeries and breweries. (Phillips 2012) in 1680, the Dutch naturalist Anton van leeuwenhock first microscopically observed yeast but at the time he did not consider them to be living organisms but rather globular structures (Huxley, 1871) in 1857 French microbiologist louis Pastear. Proved in the paper “memire sur la fermentation alcoolique” that alcoholic fermentation was conducted by living yeasts and not by a chemical catalyst. (Barntt 2003). Pasteur showed that by bubbling oxygen into the yeast broth, cell growth could be increased but fermentation was inherited as an observation cater called the “Pasteur effect”
- YEAST
Yeast is any of various one called fungi that can cause the fermentation of carbohydrates producing carbon dioxide and alcohol. Bakers put it in bread to make it rise. Yeast is also used for the production of beer and wine. Yeast that are used commercially consist of masses of microscopic yeast organism.
