yeast process production

8/3/2019 Yeast Process Production

1/32

Yeast Process Production


2/32

Yeasts can be considered mans oldest industrial microorganism.

Its likely that man used yeast before the development of a written language.

Hieroglyphics suggest that that ancient Egyptians were using yeast and theprocess of fermentation to produce alcoholic beverages and to leaven bread

over 5,000 years ago.

The biochemical process of fermentation that is responsible for

these actions was not understood and undoubtedly lookedupon by early man as a mysterious and even magical

phenomenon.

It is believed that these early fermentation systems for alcohol

production and bread making were formed by natural

microbial contaminants of flour, other milled grains and from

fruit or other juices containing sugar.

Such microbial flora would have included wild yeasts and lactic

acid bacteria that are found associated with cultivated grains

and fruits.


3/32

It was not until the invention of the microscope followed by thepioneering scientific work of Louis Pasteur in the late 1860s that yeast

was identified as a living organism and the agent responsible for

alcoholic fermentation and dough leavening. Shortly following these discoveries, it became possible to isolate yeast in

pure culture form.

With this new found knowledge that yeast was a living organism and the

ability to isolate yeast strains in pure culture form, the stage was setforcommercial production of bakers yeast that began around the turn of the

20th century. Since that time, bakers, scientists and yeast manufacturers have been

working to find and produce pure strains of yeast that meet the exacting

and specialized needs of the baking industry.


4/32

Yeasts are single-celled fungi.

As fungi, they are related to the other fungi that people are morefamiliar with.

These include edible mushrooms available at the supermarket,

common bakers yeast used to leaven bread, molds that ripen blue

cheese and the molds that produce antibiotics for medical and

veterinary use.

Many consider edible yeast and fungi to be as natural as fruits and

vegetables.

Yeast Cells


5/32

Bakers yeast is used to leaven bread throughout

the world and it is the type of yeast that people are

most familiar with.

Bakers yeast is produced from the genus and

species of yeast called Saccharomyces cerevisiae.

The scientific name of the genus of bakers yeast,

Saccharomyces, refers to saccharo meaning sugar

and myces meaning fungus.

The species name, cerevisiae, is derived from the

name Ceres, the Roman goddess of agriculture.

Bakers yeast products are made from strains of this

yeast selected for their special qualities relating to

the needs of the baking industry.


6/32

The typical yeast cell is approximately equal in size to a human

red blood cell and is spherical to ellipsoidal in shape.

Because of its small size, it takes about 30 billion yeast cells to

make up to one gram of compressed bakers yeast.

Yeast reproduce vegetatively by budding, a process during

which a new bud grows from the side of the existing cell wall.

This bud eventually breaks away from the mother cell to form aseparate daughter cell.

Each yeast cell, on average, undergoes this budding process 12

to 15 times before it is no longer capable of reproducing.

During commercial production, yeast is grown under carefully

controlled conditions on a sugar containing media typically

composed of beet and cane molasses.

Under ideal growth conditions a yeast cell reproduces every

two to three hours.


7/32

Yeast is the essential ingredient in many bakery products.

It is responsible for leavening the dough and imparting a

delicious yeast fermentation flavor to the product.It is used in rather small amounts in most bakery

products, but having good yeast and using the yeast

properly often makes the difference between success and

something less than success in a bakery operation.


8/32

In the production of baked goods, yeast is a key ingredient and serves three

primary functions:

Production of carbon dioxide:

Carbon dioxide is generated by the yeast as a result of the breakdown of

fermentable sugars in the dough. The evolution of carbon dioxide causes

expansion of the dough as it is trapped within the protein matrix of the

dough.

Causes dough maturation:

This is accomplished by the chemical reaction of yeast produced

alcohols and acids on protein of the flour and by the physical stretchingof the protein by carbon dioxide gas. This results in the light, airy

physical structure associated with yeast leavened products.


9/32

Development of fermentation flavor:

Yeast imparts the characteristic flavor of bread and other yeast

leavened products.

During dough fermentation, yeast produce many secondary

metabolites such as ketones, higher alcohols, organic acids,

aldehydes and esters.

Some of these, alcohols for example, escape during baking.

Others react with each other and with other compounds found in the

dough to form new and more complex flavor compounds.

These reactions occur primarily in the crust and the resultant flavordiffuses into the crumb of the baked bread.


10/32


11/32


12/32


13/32


14/32


15/32


16/32


17/32


18/32


19/32


20/32


21/32


22/32


23/32


24/32


25/32

The bakers yeast production process flow chart attached

before can bedivided into four basic steps.

In order these steps are, molasses and other raw material

preparation, culture or seed yeast preparation,

fermentation and harvesting and filtration and packaging.The process outlined in the flow chart takes approximately

five days from start to finish.


26/32

The basic carbon and energy source for yeast growth are sugars.

Starch can not be used because yeast does not contain the

appropriate enzymes to hydrolyze this substrate to fermentablesugars.

Beet and cane molasses are commonly used as raw material

because the sugars present in molasses, a mixture of sucrose,

fructose and glucose, are readily fermentable.

In addition to sugar, yeast also require certain minerals, vitaminsand salts for growth.

Some of these can be added to the blend of beet and cane

molasses prior to flash sterilization while others are fed

separately to the fermentation.

Alternatively, a separate nutrient feed tank can be used to mix

and deliver some of the necessary vitamins and minerals.

Required nitrogen is supplied in the form of ammonia and

phosphate is supplied in the form of phosphoric acid.


27/32

Each of these nutrients is fed separately to the fermentation to

permit better pH control of the process.

The sterilized molasses, commonly referred to as mash or wort,

is stored in a separate stainless steel tank.The mash stored in this tank is then used to feed sugar and

other nutrients to the appropriate fermentation vessels.

Bakers yeast production starts with a pure culture tube or

frozen vial of the appropriate yeast strain.

This yeast serves as the inoculum for the pre-pure culture tank,

a small pressure vessel where seed is grown in medium under

strict sterile conditions.

Following growth, the contents of this vessel are transferred to

a larger pure culture fermentor where propagation is carriedout with some aeration, again under sterile conditions.

These early stages are conducted as set-batch fermentations.

In a set-batch fermentation all the growth media and nutrients

are introduced to the tank prior to inoculation.


28/32

From the pure culture vessel, the grown cells are transferred to

a series of progressively larger seed and semi-seed fermentors.

These later stages are conducted as fed-batch fermentations.

During a fed-batch fermentation, molasses, phosphoric acid,Ammonia and minerals are fed to the yeast at a controlled rate.

This rate is designed to feed just enough sugar and nutrients to

the yeast to maximize multiplication and prevent the

production of alcohol.

In addition, these fed-batch fermentations are not completelysterile.

It is not economical to use pressurized tanks to guarantee

sterility of the large volumes of air required in these fermentors

or to achieve sterile conditions during all the transfers throughthe many pipes, pumps and centrifuges.

Extensive cleaning of the equipment, steaming of pipes and

tanks and filtering of the air is practiced to insure as aseptic

conditions as possible.


29/32

At the end of the semi-seed fermentation, the contents of the

vessel are pumped to a series of separators that separate the

yeast from the spent molasses.

The yeast is then washed with cold water and pumped to asemi-seed yeast storage tank where the yeast cream is held at

34 degrees Fahrenheit until it is used to inoculate the

commercial fermentation tanks.

These commercial fermentors are the final step in the

fermentation process and are often referred to as the final or

trade fermentation.


30/32

Commercial fermentations are carried out in large fermentors with working

volumes up to 50,000 gallons.

To start the commercial fermentation, a volume of water, referred to as setwater, is pumped into the fermentor.

Next, in a process referred to as pitching, semi-seed yeast from the storage

tank is transferred into the fermentor.

Following addition of the seed yeast, aeration, cooling and nutrient additions

are started to begin the 15-20 hour fermentation.

At the start of the fermentation, the liquid seed yeast and additional water

may occupy only about one-third to one-half of the fermentor volume.

Constant additions of nutrients during the course of fermentation bring the

fermentor to its final volume.

The rate of nutrient addition increases throughout the fermentation because

more nutrients have to be supplied to support growth of the increasing cellpopulation.

The number of yeast cells increase about five- to eight-fold during this

fermentation.


31/32

Air is provided to the fermentor through a series of

perforated tubes located at the bottom of the vessel.

The rate of airflow is about one volume of air per fermentor

volume per minute.A large amount of heat is generated during yeast growth and

cooling is accomplished by internal cooling coils or by

pumping the fermentation liquid, also known as broth,

through an external heat exchanger.

The addition of nutrients and regulation of pH, temperature

and airflow are carefully monitored and controlled by

computer systems during the entire production process.

Throughout the fermentation, the temperature is kept at

approximately 86 degrees Fahrenheit and the pH in therange of 4.5-5.5.


32/32

At the end of fermentation, the fermentor broth is separated by nozzle-type

centrifuges, washed with water and re-centrifuged to yield a yeast cream with

a solids concentration of approximately 18%.

The yeast cream is cooled to about 45 degrees Fahrenheit and stored in a

separate, refrigerated stainless steel cream tank.

Cream yeast can be loaded directly into tanker trucks and delivered to

customers equipped with an appropriate cream yeast handling system.

Alternatively, the yeast cream can be pumped to a plate and frame filter pressand dewatered to a cake-like consistency with a 30-32% yeast solids content.

This press cake yeast is crumbled into pieces and packed into 50-pound bags

that are stacked on a pallet.

The yeast heats up during the pressing and packaging operations and the bags

of crumbled yeast must be cooled in a refrigerator for a period of time with

adequate ventilation and placement of pallets to permit free access to thecooling air.

Palletized bags of crumbled yeast are then distributed to customers in

refrigerated trucks.

yeast process production

Documents