You've probably heard of the old adage "Cooking is an art, while baking is a science." So what does that mean? Why is baking a science? For starters, baking relies on chemistry and it requires precision. Throw in a handful of this or a pinch of that might work for cooking, but when it comes to baking, the outcome can change with just the slightest adjustment to a recipe.

If you are not precise when measuring baking powder, your cake could collapse; if you mix your batter using too many turns, you may end up with a hockey puck instead of a moist cupcake; and if you use butter that's a few degrees too warm in your pie crust, you could have a soggy crust.

When we bake, we rely on recipes to guide us through all the chemical reactions that take place while mixing or kneading, heating or baking, cooling or whipping. Baking involves all sorts of chemical reactions: protein coagulation, water evaporation, caramelization and browning, enzyme reactions, expanding gases, thickening starches and so on.

Take cakes, for example. Each ingredient has a job to do. The proteins in the flour bond and create gluten and this provides the cake's structure; baking powder and baking soda react with acidic and alkaline ingredients to release carbon dioxide, adding bubbles to the batter which helps the cake expand and have airiness; eggs bind all the ingredients together; butter and oil tenderize; sugar caramelizes, browns and tenderizes; milk and water provide moisture; and yogurt, juice, fruit sauces and other acidic ingredients help balance flavor, tenderize and add moisture, and they react with leaveners to help give rise.

Baking introduces your child to science in a fun and rewarding way, teaching them skills that will help them understand better how things work and the world around them.

Acidic and Alkaline Ingredients

The pH scale measures the degree of acidity and alkalinity of a substance on a scale from 0 to 14. The midpoint is seven and represents neutral; below seven is acidic and above seven is alkaline. Successful recipes have a balance of acidic and alkaline ingredients to achieve a neutral pH because this results in the best flavor and texture. Knowing the acidity or alkalinity of your ingredients and understanding how acidic and alkaline ingredients work together can help ensure your baked goods will turn out the way you intended. With practice, you will be able to develop your own recipes, which can be great if your child or another family member has allergies.

Baking soda, a chemical leavener, is alkaline and is used when there is an acidic ingredient in the recipe. Examples of acidic ingredients include applesauce, buttermilk, yogurt, honey, brown sugar, molasses, lemon juice, vinegar and regular cocoa powder (not Dutch-process or alkalized cocoa powder - which is neutral). When baking soda comes in contact with an acidic ingredient and is moistened, the alkali/acid combination creates carbon dioxide, and this helps the batter to rise.

If your chocolate cake recipe calls for buttermilk and you use regular milk, there wouldn't be a release of carbon dioxide to give it that fluffy texture that makes cake so special. The recipe likely calls for baking soda, which is alkaline, and it reacts with the acidic buttermilk to allow the cake to rise. In addition, the color of your cake and the taste won't be as appealing.

Adding the right amount is important too. If you were to add one-half teaspoon baking soda to your cookie dough when the recipe calls for one-quarter teaspoon, you might end up with over-browned, burnt-tasting cookies. And if you don't add enough, you might end up with something more like a muffin than a cookie. Too much baking soda can also create soapy off-notes, and too little will allow acidic flavors to come through too strong.

Baking powder, on the other hand, has both alkaline and acidic ingredients in it and is slightly acidic - almost neutral on the pH scale. It reacts in two phases - when moistened and when heated - and the gas won't be released until baked. You will usually see baking powder in a recipe that has an alkaline ingredient in it, such as milk, but it can be found in other carefully crafted recipes as well.

Here's how these leaveners work: the baking powder and baking soda start acting immediately when you put your cake batter in the oven. They expand the air bubbles previously beaten or mixed into the batter and held by the flour's gluten strands. At the end of baking, the flour's starches firmly set around the expanded air bubbles and the batter conforms to the shape of the pan and browns. When you cut your cake after baking, you should see tiny, evenly spaced holes or air pockets.

If the holes are big and uneven, you possibly added too much baking powder or baking soda, which can cause the gluten strands to weaken and not have the ability to hold in the excess carbon dioxide (air bubbles) before the cake's flour starches have set, thus spilling over. On the other hand, if you add too little baking powder the cake's structure may set too soon, it won't be able to rise - resulting in a hockey puck cake.

Yeast, another leavener, consumes available sugars and creates carbon dioxide as a byproduct. Whipped egg whites also act as a leavener when folded into batter.

Sugar, Salt, Eggs and Flour

Sugar has many functions in baking. It caramelizes foods when it breaks down from heat. It's also responsible for browning foods when it binds with amino acids - a process known as Maillard reaction. It also draws in moisture from the surrounding air, which helps slow the cake from hardening. When a cake begins to go stale, the starch starts to crystallize. Sugar will draw in moisture and prevent the starch molecules from forming and crystallizing.

Salt does more than just round out flavor. It draws water out of foods and in baking, it regulates fermentation. Yeast needs water to perform its function. Salt hinders the yeast and thereby slows the leavening process. It also helps strengthen the dough; without salt, the dough would be a sticky mess. The negative ions in the salt balance out the positive charge in the gluten. Too many positive charges push the gluten apart.

Eggs are filled with protein. When heated, their proteins unravel and realign to form a solid out of a liquid, giving structure to a baked good.

Flour has two types of protein - glutenin and gliadin. When water is added to flour, the proteins come together to form a new protein called gluten. When heated, the starch portion of the flour gels with the help of sugar and creates a web-like structure that traps water and provides moisture. The carbon dioxide from the leavener expands the cake and the gluten holds the bubbles in place.

It's important to know the protein content of flour. For example, you don't want to use a high-protein flour when making cookies. High-protein flour has more gluten than all-purpose flour and is better suited for bread as it gives strength and structure. Cookies are crumbly, chewy and crunchy. They need a lower protein flour.

There is a lot more science in baking than what we covered here - emulsification, friction, air pressure and heat are just a few things you'll learn if you bake frequently. If you know your ingredients and how they behave, you'll have a good chance at success.

Jennifer Poole is Assistant Editor at Washington Parent.