Saccharomyces because of its unique physiology and the

Saccharomyces cerevisiae (yeast) is a
sugar fungus used in different types of foods and beverages because of its unique
physiology and the key roles it plays in food fermentations. Yeast is naturally
found growing on the skins of fruits, plant leaves, surface of the skin, in the
intestinal tracts of warm-blooded animals, soil and on flowers. However, this
yeast is found in the skins of grapes and other fruits. Most yeasts will thrive
best in a neutral or slightly acidic pH environment and each type of yeast has
slightly different temperature range. Saccharomyces cerevisiae’s growth
temperature is between 32.3°C-45.4°C and can survive in the presences or
absence of oxygen. In the presence of oxygen, the yeast will undergo aerobic
respiration, converting carbohydrates into carbon dioxide and water. Luis
Pasteur was the person who first identified and used saccharomyces cerevisiae as
the key microbe for wine and bread making in 1856. It was around a year later
when it became popular for most industries to use it. This type of yeast has been
genetically manipulated and engineered to suit the specific needs for the fermentation
process. Saccharomyces cerevisiae has been labeled as GRAS (generally regarded
as safe) and is the most common yeast out there for food and beverage making.
It has been studied as a eukaryotic model organism and was the first to
completely sequence.

Saccharomyces cerevisiae chemical
formula is C:H (1.612): O (0.557): N (0.158). This means for every 1 mole of
carbon, there is 1.613 moles of hydrogen, 0.557 moles of oxygen, 0.158 moles of
nitrogen. On a much smaller scale, there is also 0.012moles of phosphorus,
0.003moles of sulfur, 0.003 moles of magnesium, 0.022 moles of potassium, and
0.001 of calcium.

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Fermentation systems ranged from
opened and closed squares to horizontal and vertical cylindrical vessels. The
most common style for batch is the cylindroconical fermenter, an enclosed
vertical cylindrical vessel with a cone shaped base because they are cheaper to
purchase and operate, the efficiency of production, and it doesn’t take up a
lot of room. Before any beer can be made, all the equipment must be sanitized,
and the operator must maintain good hygiene to ensure low unwanted microorganisms
getting into the beer. The chosen grain and barely are placed into a cheese
cloth and into the water.


They undergo mashing; the steeping of
grains, releasing the flavours and sugar that are needed for the fermentation
process. The mixture is heated and held at different temperature for periods of
time to activate the enzymes in the grain to convert the starches to
fermentable sugars (glucose, sucrose, fructose). This process can take up to
1-2 hours and as the result, the mixture is now mashed. The mixture now
consists of the freed starches and sugars. The cheese cloth with the grains are
removed, leaving the mixture of water and sugars, known as wort. The wort goes
through the boiling process for 45-90 minutes. Hops are added as a bittering
agent and to add aroma of the beer for 15 minutes or until “flame out”. Flame out
is when the heat source is either turned off or the boiling has stopped. The longer
the hops are in, the more of the piney or fruity smells are present in the
beer. The aroma and flavor of the beer depends on the kind of hop used. The
mixture must be cooled before the saccharomyces cerevisiae can be added because
it is temperature sensitive. This type of yeast can undergo both aerobic and
anaerobic respiration. For Fermentation, the yeast starts breaking down the
different forms of sugar present in the wort. The sugars are typically monosaccharides
glucoses and fructose which contain a single hexose (a 6-carbon chain). The
disaccharides present are typically galactose, sucrose, and maltose. The trisaccharide
present is maltotriose. The yeast first breaks down the monosaccharides by
using different enzymes both inside and outside the cell. Sucrose is broken
down into glucose and fructose by the invertase enzyme.  Once the complex sugars are broken down into monosaccharides,
the yeast can use them. In the presents of oxygen, aerobic respiration occurs
in the mitochondria of the yeast. Using other enzymes, two pyruvates produced
from glycolysis, are decarboxylase to form acetaldehydes and carbon dioxide. Last
step is to had hydrogen ions to the aldehyde to form ethanol. The hydrogen atom
is from the NADH made during glycolysis and converts back to NAD+. This forms a
defense that will make sure no bacteria growth on the mixture. However, some
bacteria are purposely added to the mixture for different tastes. Some breweries
used open fermentation vessels, which can expose the beer to infection but
improve the process of removing the yeast. On the industrial scale, the yeast
is removed by filtration and bottled. Conditioning and carbonation occur in a
secondary container, so the beer is not exposed to the dead yeast.


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