Virtual Open Schooling Online courses available at Virtual Open Schooling (VOS), for more details kindly click here!
NIOS Silver Jubilee Year

Leavening Agents

Jump to: navigation, search

Mindmap.pngConcept Map

Conceptmap leavening.png


This OER enables you to:

  • Describe function of leavening agent in food preparation
  • Differentiate between types of yeast
  • List ingredients and proportion required for bread making
  • List precautions that need to be taken while using yeast



Let’s solve the Meena’s problem now by understanding the role of yeast in bread making. What is yeast? What are leavening agents? How does yeast react with other ingredients? What precautions should we take while using yeast?

Leavening agents –

Yeast is a leavening agent. Leavening agents are those materials which give products like cakes, breads, cookies, a rise and increase them in volume, gives shape and adds texture to the product. Leavening is production or incorporation of gases in the baked product. Leavening agents serve following purposes;

  1. makes the products light and spongy
  2. makes product digestible
  3. makes it soft and can be chewed easily
  4. makes it tastier and appetizing

Types of leavening agent

  • Chemical – baking powder, sodium bicarbonate, ammonium bicarbonate (by releasing carbon dioxide gas)
  • Biological – yeast (by fermentation)


  • Mechanical – beating, whisking (by means of air)

Mechanical leavening.jpeg

  • Lamination – rolling, folding
  • Steam – water vapour pressure

Functions of leavening agents in bakery products –

  • It increases the volume of the product.
  • It improves the product by making it tender and lighter.
  • It improves the crumb color, softness of the texture, taste and smell.
  • It improves the digestibility.

Visit following sites for more information


Yeast –

Yeast is a unicellular organism. It is biologically named as Saccharomyces Cerevicae (also called baker’ yeast). It was discovered by Louis Pasteur in the year 1859. Yeast is used for fermentation of bread, beer, and wine and is used in baking and fermenting of alcoholic beverages. Under favourable conditions, yeast cells multiply by a process called budding and produce CO2 gas and alcohol.

Production of yeast –

To produce bakers’ yeast the first requirement is to make a medium in which the yeast can grow. For this purpose two types of mediums are used. 1. Medium consists of a solution of molasses to which diammonium phosphate and acids are added. 2. In the second medium, barley is used. The barley is broken into small particles and soaked in water. Steam is passed through the mixture to gelatinized starch present in barley. Care must be taken not to boil the mixture and the temperature is kept 60˚C. With the help of enzymes the starch is converted into maltose and dextrin. When this liquid is poured into a large filler tank and wort or pure yeast culture is added. The temperature should be 27˚C. A little lactic acid is also added which prevents other bacterial growth. The pure yeast grows and increases in quantity. Air is passed through this mixture to quicken the process. Under this favourable condition the yeast grows rapid by budding. Several millions of yeast cell are grown in this manner. They are separated and collected by a machine and are packed in packets.

Types of yeast -

Dry yeast Yeast.jpeg Compressed yeastFresh yeast.jpeg
It is available in the granular form, and available packed. It is called as fresh yeast, or wet yeast.
It has a longer shelf life. Storage- up to six months at room temperature This has short life as 1 week of storage in the refrigerator
It has finer particle size It is available in a block form.

It is available in the granular form, and available packed. It is called as fresh yeast, or wet yeast. It has a longer shelf life. Storage- up to six months at room temperature This has short life as 1 week of storage in the refrigerator. Dry yeast causes rapid rising of the dough. It has finer particle size It is available in a block form.

Yeast + H2O + sugar + right temperature = fermentation (CO2)

Factors affecting process of bread making and reaction of yeast


Sugar.jpeg Sugar is food for yeast and it helps yeast to raise the dough. Ideally it is said that sugar concentration should not exceed 10 percent based on flour in dough using 0.5 to 1.0 percent yeast. Above this level yeast cell are destroyed due to high osmotic pressure exerted by sugar.



Salt controls the activity of yeast during fermentation and it has tightening action on flour protein. It should be dissolved completely before use as powdered salt or too much salt inhibits yeast activity, reducing the amount of carbon dioxide gas produced and decreasing volume of the dough.



Yeast cells are living cells. Water used in the process of bread making should be lukewarm as it provides favourable temperature for activity of yeast. Higher temperature of water can kill yeast resulting in no leavening. carbon dioxide is produced in the dough when yeast is added. Yeast is very sensitive to temperature fluctuations. Kneading the dough is done to develop the gluten. Gluten gives texture and elasticity to the bread.

Proving chamber


Proving chamber is a cupboard where temperature is set for yeast. So dough rises properly and yeast ferments at right temperature. After proving process is done dough should be handled gently so that the carbon dioxide gas formed in side should be retained to give desired texture to the product.

Methods of using yeast

Straight dough method

In this method 1 % of yeast is used and all the ingredients are incorporated in one long process of mixing and kneading. Dough is allowed to rise four times.

No time dough method

2 – 6 % of yeast is used in this method. Bakers use this method when they are in a hurry. The bread may have a strong yeast flavor due to more quantity of yeast present in the dough.


Production of carbon dioxide gives volume to the bread. Dough contains gluten which stretches and allows the dough to rise evenly by the expanding gases and at the same time retains them. Yeast grows best in the temperature 25˚ to 33˚ Celsius. Yeast slows down below 10˚ Celsius.

During winter percentage of yeast in the recipe should be increased. If dough requires long fermentation period to develop flavor in bread then one should reduce the yeast content. If dough requires fast fermentation the quantity of yeast should be increased to make the dough light and spongy.


1.Find examples of Bakery products where yeast is used. You may visit any bakery unit to know about this.

2. Also find out What happens if you use too much of yeast in bread making?

3. What will happen if you use too little yeast in bread making?

Precautions to be followed while using yeast:

Look at this bread sample. Would you buy it?

Let us know more about yeast that enhances quality of product

  • Yeast should have a pleasant, fresh, characteristic smell and taste. The smell should be yeasty, but not sour.
  • You should use lukewarm water for bread making. If the water is too hot then it will kill the yeast. And if the water is cold it will take long time to ferment the bread.
  • Fresh and quality yeast when mixed with water it should disperse quickly and easily therefore one should use fresh yeast.

Selection of fresh yeast

Over proving

  • We should avoid over-proving the dough as it will affect the quality and texture of the desired product, as over-proving creates too much carbon di-oxide in dough, which tries to escape from it.
  • The picture below shows an over proved dough


Dry yeast should be stored in air tight containers and away from heat. Compressed yeast should be stored in refrigerator and used within 1 week. Yeast should not be stored at high temperatures as this damages the cell.


  • Leavening is the increase in surface area of a dough or batter by the aerating agents such as air, carbon dioxide and water vapour. Baked goods can be leavened by biological, chemical mechanical, lamination and combination of above methods.
  • Not only yeast but also other ingredients play a vital role in fermentation process of bread making
  • Dry yeast or fresh yeast serves the same purpose, only shelf life is different.
  • Adding right amount of yeast and appropriate way of proving will give the bread good color, texture and taste.
  • Storage and application of yeast should be done at correct temperature ranges to get desired quality products.

Inkpot.png Assignments

Geeta is trying to make bread first time. She added boiling hot water to the yeast so it will rise quicker. Find out what must have happened during the fermentation. You may try yourself and write down suggestions to Geeta.