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�Leavening agents are products that release gaseous substances, which give the dough its porosity.�

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Raising agents

Raising agents include anything that causes rising within foods and are usually used in baked goods.

Raising agents are added to baked products during the preparation stage. They create gas, air or steam which expands when heated and causes the food to rise.

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Raising agents

When heated, the gas that is trapped within the product expands. This is because heating causes the molecules in the air to move more rapidly and apply more force.��This rising results in a light and airy texture within foods.

Examples of mixtures that require aeration are:

cakes, bread, batters, pastries, meringues, soufflés.

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Different types of raising agents

There are different types of raising agents that can be used.

These can be:

mechanical;
chemical;
biological.

Different foods may use one or more of these to achieve a desirable end product.

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Mechanical raising agents

Air is a commonly used and effective raising agent. It can be added to a mixture in a variety of ways:

sieving flour or lifting flour when rubbing in fat, e.g. pastry, scones, cakes;
creaming fat and sugar to incorporate air, e.g. creamed cake mixture;
whisking to trap air e.g. eggs, whisked to create a foam for sponge cakes, meringues, soufflés;
beating ingredients together helps to trap air, e.g. beating eggs into a creamed mixture;
rolling and folding pastry (creating laminations) traps air, e.g. flaky pastry, rough puff pastry.

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Steam as a raising agent

Steam is a common physical raising agent. It is produced from the liquids (e.g. water, milk, eggs) that are added to mixtures, or from water contained in a solid component (e.g. butter). ��Examples of recipes which use steam as a raising agent are batters (e.g. Yorkshire pudding) and choux pastry. They require a high oven temperature to produce the steam to raise the mixture.��This produces a light, open texture with large pockets of air left after the steam has escaped.��Steam also works with air and carbon dioxide in cakes and bread, as well as with air in pastry, to help increase their volume.

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Chemical raising agents

Chemical raising agents are those that require a chemical reaction to function. Common examples of chemical raising agents include:

baking soda (bicarbonate of soda);
baking powder (bicarbonate of soda + cream of tartar);
self-raising flour.

�Baking soda is an alkali that reacts with an acid (in the presence of water) to produce carbon dioxide, which causes rising. Baking powder is baking soda with an acid (e.g. cream of tartar) already present, so only water need be added.

Self-raising flour is flour that already contains baking powder, and therefore only requires water to be activated.

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Biological raising agents

Yeast is a biological raising agent. There are different types of yeast available that can be used to make bread and bread products. These are: fresh yeast, dried yeast and easy-blend yeast.

Given the right conditions (warmth, carbohydrates and moisture) yeast converts sugars to alcohol and carbon dioxide. This is called fermentation.

The carbon dioxide in the bread dough will expand when placed in a hot oven; steam is also produced to help raise the dough.

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Yeast consists of microorganisms (yeast fungi) made up of individual, non-motile cells that multiply very quickly under favorable conditions.

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Biological raising agents

Yeast is dissolved in water at a temperature of 30~35*С
Dry yeast is sold as a powder, granules, or tablets. It has a yellowish-gray color and a moisture content of 8-9%.
The shelf life of fresh pressed yeast in the refrigerator is only 12 days, while dry yeast lasts about 6 months, and some instant yeast can last as long as 5 years.
When preparing yeast dough, the yeast ferments the sugars into alcohol, and carbon dioxide is produced. As a result of the development of these microorganisms, the dough acquires a sour taste.

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Biological raising agents

The conditions that affect yeast fermentation are:

temperature: the best temperature range for yeast is between 25° - 35°C. If the temperature is too high the yeast cells are destroyed, if too low the action is slowed;
moisture: this is provided by the liquid in the dough; this should be at the correct temperature;
food: this is supplied by the starch in the flour.

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Biological raising agents

Other ingredients can also affect the action of the yeast. These include:

salt: excess will slow the action of the yeast by drawing the water out of the cells and destroying them;
fat: a high fat content will slow the action of the yeast; rich dough recipes often have a higher proportion of yeast to flour;
sugar: normally, adding sugar will speed up yeast growth, but large excesses of sugar can bind water and actually inhibit yeast growth.

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Combining raising agents

The different types of raising agents are sometimes used together to aerate a mixture.

A creamed cake mixture is a good example.

This uses:

mechanical: air is added by sieving the flour, creaming the fat and sugar, beating in the egg;
physical: steam is formed from the liquids during cooking;
chemical: carbon dioxide is released from the baking powder or self-raising flour when the liquid is added and during cooking.

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How raising agents work - summary

The appropriate raising agent is added to the mixture and is evenly distributed. When it is heated one or more of the following will take place:

air will expand;
steam is produced from liquids and enlarges the air cells, the steam escapes and is replaced by air;
carbon dioxide is produced when moisture and heat act on baking powder (or similar), the carbon dioxide enlarges the air cells and aerates the mixture. The gases expand when they are heated;
carbon dioxide produced by yeast cells expands due to the heat of the oven.

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How raising agents work

Additional information�

gluten in flour allows mixtures to stretch as the reactions take place;
mixtures must rise before the protein in the flour/egg coagulates during the cooking process;
when coagulation takes place, the mixtures sets in its risen shape.

The type of raising agent used will affect the final texture and appearance of the dish.

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Raising agents

https://youtu.be/2NOokxWpFgw

This resource meets the Guidelines for producers and users of school education resources about food.

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What is the purpose of leavening agents in dough:�a) impart porosity; b) improve flavor; c) change color;�2. What type of leavening does yeast do?�a) mechanical; b) biological; c) chemical��3. At what temperature is yeast diluted with water?�a) 30-35; b) 20-25; c) 45-50 degrees�4. What type of mechanical leavening agent is used?�a) egg whites; b) yeast; c) baking soda�5. What type of leavening method is used to make shortcrust pastry?�a) mechanical leavening; b) biological leavening; c) chemical leavening.�6. What type of yeast can be stored for longer than 6 months?�a) compressed; b) dry;