What Are Chemical Raising Agents?

While most of us are familiar with baking powder, there are many other chemical raising agents used to make bread, cake, and pastries. Also known as leavens, these different forms of raising agents release carbon dioxide during the baking process, causing bubbles and foaming to occur. This is what gives baked goods their light, fluffy texture. Although a simple enough concept, there’s a lot more happening beneath the surface than you might think, and it all comes down to the chemical reactions taking place.

Chemical Raising Agents Explained

There are several different raising agents used in baking, but in all cases there is one main principle: to create thousands of small air bubbles in the dough or pastry. This can either be done mechanically, biologically, chemically, and even with the use of steam or lamination. Here’s how each method works:

• Mechanical: This involves beating egg whites quickly until bubbles are created, which are essentially pockets of carbon dioxide. The egg whites can then be mixed with the dough.
• Biological: Yeast is commonly used to produce carbon dioxide in bread dough because it ferments sugars. This happens by the yeast feeding on the dough and releasing carbon dioxide.  
• Chemical: Chemical raising agents are the quickest and most popular way to aerate a baking mixture. ‘Leaveners’ produce carbon dioxide by reacting with water and acidic ingredients.
• Self-raising flour: This is a variant of using chemical raising agents. because this flour already contains baking powder. This means there’s no need to add any more raising agents to the mix. 
• Steam: Steam is also used to create air pockets inside dough or batter. This is the most common method used when cooking puddings, cantonese dumplings, and cha siu bao (steamed buns with meat fillings).
• Lamination: This is the method used to make croissants. In a nutshell, alternating sheets of dough and butter are rolled out. When folded, the butter becomes fully sealed within the pastry. This causes all the moisture to evaporate during baking, providing a lift to the pastry.  

While all of these are viable options, using raising agents is the most straightforward method. In the case of baking powder or baking soda, for example, carbon dioxide is released from the bicarbonate with the help of acidic catalysts, like yoghurt and buttermilk. The heat from the oven also helps the carbon dioxide bubbles to expand further, thereby raising the dough.

The other ingredients used in dough, pastry or batter mixtures, such as eggs, milk, and sugar, don’t usually chemically react with baking powder or other leavens. Instead, it’s the water that facilitates the chemical reaction because it causes the baking powder to form ions. Interestingly, the effect of combining baking soda with water can also be used to ease indigestion or heartburn because of its behaviour as an antacid. Commercially available baking powder is a mixture of sodium bicarbonate and potassium bitartrate (cream of tartar to you and me), as well as an alkaline and an acidic ingredient.

How Do Chemical Raising Agents Work?

Chemical raising agents are usually alkalis, and they work by reacting with acidic ingredients, like milk, to produce carbon dioxide. When dry, the alkaline and acidic substances may already be combined in the mixture, but they’ll be unable to react because they won’t be in ionic form. Only once water or moisture is added can the acid-base reaction occur. 

This reaction is slow at first, but it accelerates when the dough is baked inside the oven. During this process, the introduction of heat does more than speed up the chemical reaction – it also causes the pockets of gas to expand, forming larger bubbles. This means that while the dough grows in size, it becomes significantly less dense. Basically, the bigger the air bubbles, the lighter and fluffier the product. A cake, for example, has a lot of bubbles in it, which is what makes it less rigid than, say, bread. 

What Chemical Raising Agents Are There?

There are three main types of chemical raising agents used in baking. To achieve the right texture and structure for whatever it is you’re baking, it’s important to use the right kind of leaven. Here’s more about each one:

• Baking soda: Also known as bicarbonate of soda or sodium bicarbonate, this is probably the most popular and readily available chemical raising agent. It’s commonly used in soda bread and gingerbread. With the chemical formula NaHCO₂, this alkali is also used in many other applications besides baking.
• Baking powder: This is often confused with baking soda, and many believe they’re the same product, but there are distinct differences between these two leaveners. While baking soda is a base that reacts with acidic ingredients, baking powder is a mixture of baking soda and a dry acid, usually cream of tartar. This means that baking powder doesn’t need an additional acidic ingredient in order to react and produce CO₂. Because of this, baking powder is also the key ingredient in self-raising flour.  
• Cream of tartar: This is an acidic substance that is chemically known as potassium hydrogen tartrate, or potassium bitartrate (KC₄H₅O₆). As we just explained, this is combined with bicarbonate of soda to produce baking powder. In this dry powder form, cream of tartar and baking soda are stable – but they react once they’re dissolved in water, or when they’re mixed with a moist dough. Cream of tartar is also often added to whipped egg whites or whipped cream in order to stabilise them while increasing their volume. 

How Should Chemical Raising Agents Be Stored And Used?

Chemical raising agents are stable as long as they’re kept in a dry environment. Since these agents react with water, any amount of moisture is dangerous. Baking soda, for example, has an exothermic reaction with water that produces carbonic acid, so keeping it in a dry cupboard away from moisture is the best way to lengthen its shelf-life.  

Temperature is also an important factor. Even when sealed, chemical raising agents should be stored at moderate room temperature. If exposed to heat, like direct sunlight, they can potentially be ruined. Additionally, caking of the powder may occur if a chemical raising agent is stored for a very long time, and the powder becomes very compacted. 

So, when using a leavening agent:

• Make sure that it has been stored in a cool, dry place – but if it’s been in your cupboard for a few years (yes, we’ve all been there), it might be time to purchase a new one
• Only use the amount specified by the recipe; excess amounts can potentially ruin the taste of the bread, cake or pastry you are baking 
• Make sure that the acid-base reaction has completed as much as possible so that the optimal amount of carbon dioxide gets released 
• Thoroughly mix the chemical raising agent with the dough or batter so that it’s evenly distributed. This also happens when you knead or roll it out

While we’re on the subject, when a dough is kneaded it becomes more elastic. This happens because two proteins inside the mixture (gliadin and glutenin) combine to form gluten. So kneading and rolling are not only necessary to distribute the chemical raising agent, but also to create structure and strength of the dough.

This means that when dough is baked, its internal structure won’t readily collapse, despite the thousands of bubbles produced by raising reagents. Instead, the gluten strengthens the dough with its protein chains, which, coincidentally, are also what make bread and other baked products classed as high-energy food.