We all encounter yeast in our day to day life. Yeast is everywhere and man has found very many uses for it. But since it is an organism capable of virulence; control is lost and the yeast causes infection and makes man sick. It is therefore beneficial if we all first understand just exactly what we are dealing with here…

What is yeast?

Dutch naturalist Antoine van Leeuwenhoek in 1680 was the first to microscopically find the existence of these organisms but of course when he did find them he believed them to be non living. It was only 177 years later in 1857 that our greatest Louis Pasteur the French microbiologist who discovered the role of yeast in the production of alcohol.

“Yeast” is derived from the Old English gist, gyst, and also from the Indo-European root, it means to boil, foam, or bubble. One of the earliest domesticated organisms, man has used yeast for fermentation and baking throughout history. Archeologists and other historians have discovered ancient breweries and yeast making chambers from civilizations much much before us. It’s truly amazing to see the knowledge and ways of our ancestors.

These chemoorganotrophs are microbes which utilize organic compounds as their source of energy not like plants which require sunlight to grow. And unlike certain anaerobic bacteria which can survive in the absence of oxygen; yeast is a microbe very much in need of it; they may have an anaerobic component but can never be truly anaerobic. Their main source of carbon is derived from glucose, fructose, and maltose; they can metabolize ribose, alcohols and organic acids.

These microbes are temperature sensitive… As in they function in a temperature range of 10-37° with best results between 30 -37 °. Above this temperature the microbes become stressed and won’t divide properly. Above 50 they are incapable of surviving and hence this can be used to our advantage to control the pathogens. Freezing also causes a similar effect making them lazy and incapable of normal function, decreasing their viability.

I’m sure one or most of us would have the experience of finding yeast growths in odd places… Like in our food boxes which get locked up and left behind for some time when the holidays begin. The sheer joy of holidays makes forget to actually empty out our bags and then go have fun. For us the fun must begin right away right then lest it get snatched away by some unexplainable source… ? anyway as a result of this days later when we do get opening to emptying out that bag to get all neat and nice for reuse; that is when we find our scary looking friend- yeast. There are ubiquitous microbes which will set up camp at the closest favorable environment. Fruits like grapes, apples, peaches, some plant saps, cacti.

Therefore growing these organisms for various applications requires providing them with adequate environment so they help us when we help them. As long as this remains a two way street things move smoothly. In the laboratory in order to grow yeasts solid growth media or liquid broths are utilized- potato dextrose agar [PDA] or potato dextrose broth, Yeast Mould agar or broth (YM), Yeast Peptone Dextrose agar (YPD] etc… man’s other greatest discovery yet antibiotics [cycloheximide] are used to weed out certain species like Saccharomyces yeasts to grow the more wild varieties for research purposes. These organisms have sexual and asexual ways of reproduction. Asexually they either develop by binary fission or budding.