There are several kinds of leavening agents which fall into the categories: natural leavens, chemical leavens and mechanical leavening.
|The three most common leavening agents displayed.|
There is one natural leaven that we use: yeast. Yeast is a living organism which, given moisture, will convert sugars into gas. This gas is trapped in the gluten of the dough, which creates the air pockets we see in our breads. Yeast requires moisture and sugar to activate and will often ask for warmer temperatures to speed up the rising process. Generally it takes 1-2 hours for a dough to double in size. There are several types of yeast such as fresh, dried, fast-action dried and easy blend dried yeast. Most people will prefer a dried yeast because of the ease of use and storage, but fresh yeast is considered to be superior in flavour and reliability. Because of it's pronounced taste, yeast is most often used in savoury items.
Not always does one need to add yeast to benefit from it's leavening properties. Yeast spores occur naturally in flour, dairy products, plant matter, spices and even the air around us. Sourdoughs rely on these wild yeasts. With enough flour and water a batter will start to ferment spontaneously if it is given sugar or starch to feed it. This type of dough can be used for a long time if it is occasionally fed with flour and water to keep the process going and will even become more flavourful over time.
|Buttermilk scones made with baking powder and baking soda|
For most of our sweet bakes we turn to chemical leavens. Unlike yeast, chemical leavens don't create airpockets of their own, but instead they release carbon dioxide. This carbon dioxide will quickly saturate the dough and is then released into the air. This enlarges the air bubbles that are already present in the batter through mixing, creaming, whipping and beating the ingredients.
One of these chemical leavens is Baking Soda or Bicarbonate of Soda. Baking soda requires moisture and an acidic component to activate. Acidic ingredients include yogurt, buttermilk, chocolate, citrus juice, fruits, honey, sour cream, cream of tartar and molasses. When baking soda comes into contact with one of these acids and moisture, there is an instant reaction of chemicals and the leavening process is started. Because of it's fast acting nature baking soda is always added last to a batter, which is placed in the oven shortly after. The heat of the oven sets the gluten and proteins around the air pockets before it has a chance to collapse.
Another chemical leaven we often use is baking powder. This is the agent used in self-raising flour. Baking powder is a mixture of baking soda and acidic chemicals (often cream of tartar). It has the same properties as baking soda, but because it includes it's own acidic component, there is no need of including any acidic ingredients. Baking powder comes in two variations: single-acting and double-acting. Single-acting baking powder works the same as baking soda instead simply requiring non-acidic ingredients. Double-acting baking powder, just like baking soda and single-acting baking powder, starts it's leavening process once it comes into contact with moisture. Unlike the other two however, double-acting baking powder continues it's leavening process once the batter is heated in the oven.
|Baking powder in action.|
There are still more natural and chemical leavening agents to discuss, however these aren't used as often. Think of brewer's yeast or ale barm. This was the only known leavening agent until around 1800. Because of it's bitter taste it is no longer used for bread making, but you may still find it in old recipes. Baker's ammonia or hartshorn is another leavening agent you will rarely hear of. It is a type of baking powder, which gives very light and airy textures as result and is most often used in German or Scandinavian cookies. Pearlash or potash is another unknown leaven similar to baking powder, often used together with baker's ammonia. In most modern recipes these two leavens have been replaced by baking soda.
There are sponge cakes, pound cakes, soufflés and a lot of other baked goods that will rise without using any of the leavening agents we mentioned above. Through the 'mechanical process' of mixing, creaming, whipping and beating our ingredients we incorporate air into our batter. Once the batter is baked the moisture in the batter will turn to steam which increases the size of the air pockets, at the same time the gluten will harden and trap the air inside. But there is a magical ingredient here: eggs. Eggs, especially the whites, can hold a lot more air than any of your other ingredients can achieve. The elasticity of the proteins in the egg will ensure the air stays in the batter. Egg proteins tend to set fairly quickly when heated (around 70°C/160°F), thus trapping the air inside before it has a chance to collapse. Eggs also provide a lot of steam to enhance the leavening. Thus eggs cause cakes to rise through the incorporation of air before baking and providing steam during baking as well as ensuring the batter does not collapse by setting quickly.
|Savoiardi are made with only sugar, flour and eggs, yet still rise.|
Bread by Christine Ingram and Jennie Shapter
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