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The Food Lab: Baking Powder vs. Baking Soda

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Fluffy pancakes. [Photographs: J. Kenji Lopez-Alt]

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Baking powder and baking soda. Both of them are used so frequently in quick baking projects that unless you are a recipe developer, rarely do you consider what each of them actually does for your finished product. How come my scones call for baking powder, but my buttermilk biscuits call for a mixture of powder and soda? Is there an easy way to substitute one for the other if I don't have both on hand? And why do I have to bake my muffins right after mixing the batter?

This edition of the Food Lab is a quick and dirty guide to how they work, and how they affect the outcome of your recipe. For those of you who want an even quicker and dirtier guide, jump straight to the summary at the bottom of the page.

Back to Bases

Before we jump straight into the mix, let's take a quick look at the structure of leavened breads. I promise the science won't be too unbearable.

When you get down to it, leavened bread is simply a ball of protein filled with gas*. When flour is mixed with a liquid, two proteins naturally present in wheat called glutenin and gliadin link together to form a stretchy, resilient matrix known as gluten. Without a leavening agent—something to fill that gluten with air—baked goods would be nearly inedible.

*Side note: my bulldog puppy could also be described as a ball of protein filled with gas.

With traditional or "slow" breads, that leavening agent is a living fungus called yeast. As the yeast consumes sugars present in the flour, it releases carbon dioxide gas, forming thousands of teeny tiny air pockets inside the dough and causing it to rise. Once you pop that dough in the oven, those air pockets heat up and further expand, and a phenomenon known as oven spring takes place. Finally, as the gluten gets hot enough, it sets into a semisolid form, giving structure to the bread, and turning it from wet and stretchy to dry and spongy.

The only problem with yeast? It takes a long, long time to work. Enter baking soda. Unrestricted by the protracted timeframes of biological organisms, it relies instead on the quick chemical reaction between an acid and a base.

Baking soda is pure sodium bicarbonate—an alkaline powder (aka, a base). When dissolved in liquid and combined with an acid, it rapidly reacts, breaking down into sodium, water, and carbon dioxide. Just like with yeasted breads, this carbon dioxide expands upon baking, lightening the gluten protein matrix.

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This type of chemically-leavened bread is referred to as a "quick" bread, and is a broad category that includes everything from scones and biscuits, to banana or zucchini bread, and even pancakes.

Of course, for baking soda to work, a recipe needs to include a significant acidic ingredient. That's why you see so many classic recipes for buttermilk pancakes and biscuits or cake recipes that contain vinegar. The buttermilk is not just a flavoring agent—it provides the necessary acid to react with the baking soda and leaven the bread.

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Around the turn of the century, it was realized that rather than relying on the home cook to add an acidic ingredient to react with the baking soda, it'd be much simpler to add a powdered acid directly to the baking soda itself, and baking powder was born. Composed of baking soda, a powdered acid, and a starch (in order to absorb moisture and prevent the acid or base from reacting prematurely), baking powder was marketed as the all-in-one solution for busy housewives. In its dry state, it's totally inert. But once you add a liquid, the powdered acid and base dissolve and react with each other, creating bubbles of carbon dioxide without the need for an external acid source.

Neat, right? Of course, just like marriage and 24, it's not quite that simple.

All Your Base

The most interesting side effect of using baking soda in a recipe is that it affects browning in a major way. The Maillard reaction, named after Louise-Camille Maillard who first described its processes in the early 20th century, is the set of reactions responsible for that beautiful brown crust on your steak and the deep hue of a good loaf of bread. Asides from cosmetics, the reaction also produces hundreds of aromatic compounds that add an inimitable savoriness and complexity to foods.

As it turns out, the reaction occurs better in alkaline environments, which means that once you've added enough baking soda to neutralize the acid in a batter or dough, any extra you add will work to increase browning.

I made five batches of pancakes using identical batters made with a cup of flour leavened with a half teaspoon of baking powder, along with an egg, a cup of buttermilk, two tablespoons of melted butter, salt and sugar, and varying amounts of baking soda, starting with none, and increasing in 1/8th teaspoon increments up to a full half teaspoon.

Each pancake was cooked on a preheated griddle for exactly 1 1/2 minutes per side. The results very clearly demonstrate the browning effect of baking soda:

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The pancake all the way on the left is inordinately acidic, due to the un-neutralized buttermilk. It cooked up pale and bland. It was also under-risen with a flat, dense texture. The one all the way on the right, with a full half teaspoon of baking powder had the opposite problem. It browned far too quickly, lending it an acrid burnt flavor tinged with the soapy chemical aftertaste of unneutralized baking soda. Interestingly enough, this pancake was also flat and dense—the inordinate amount of baking soda reacts too violently when mixed into the batter. The carbon dioxide bubbles inflate too rapidly, and like an overfilled balloon, the pancake "pops," becoming dense and flaccid as it cooks.

The best pancake was the one right in the center with 1/4 teaspoon of baking soda. It cooked to a beautiful golden brown with a tender, well-risen crumb and had a clean buttermilk flavor.

This browning phenomenon isn't just limited to pancakes, of course. Cookie recipes routinely include baking soda to aid browning—even when there isn't an acid for them to react with. The Colombians rub pork skin with baking soda before cooking it into crispy chicharrones, in part to increase flavorful browning (as Chichi will demonstrate later this week).

Double Bubble

If there's one major drawback with chemically leavened breads, it's that they need to be cooked pretty much immediately after they are mixed. Unlike a yeasted bread dough, which is generally low in moisture and kneaded until a tough, elastic gluten network forms to trap in the massive amounts of carbon dioxide produced, a quick bread dough must be made with an extremely moist batter—baking powder simply doesn't produce enough gas to effectively leaven a thicker dough. Batters have relatively little gluten formation, meaning that they aren't all that great at trapping and holding bubbles. Once you mix a batter, your baking soda or baking powder immediately begins producing gas, and that gas almost immediately being trying to escape into the air.

So your goal is to cook the batter and set the proteins within it before the gas has time to fully escape.

Take a look at these two pancakes, both made from the exact same batch of batter:

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The first one was cooked within a few minutes after mixing, resulting in a light, tall, fluffy interior. I then let the batter sit on the kitchen counter for 30 minutes before cooking the second pancake. As you can see, the second pancake is dense, gummy, and altogether unpleasant.

But wait a minute—there are still some bubbles in there, right? Where did those come from?

Well, pretty much all baking powder is what is referred to as "double acting." Just like the name denotes, it produces gas in two distinct phases.

The first occurs right when you mix it with water. The sodium bicarbonate and one of the powdered acids, typically potassium bitartrate (a.k.a. cream of tartar) dissolve and react immediately, producing the first batch of bubbles. The second phase of the double act occurs only at higher temperatures (around 170 to 180°F), when a second powdered acid (typically sodium aluminum sulfate) reacts with the remaining sodium bicarbonate, producing another round of bubbles.

You can see that in action for yourself by performing the following easy experiment (see the image below):

1. Put a teaspoon or so of baking powder into a small bowl.
2. Add a couple of tablespoons of water. You'll notice that the baking powder immediately starts bubbling and fizzing (if it doesn't, throw out your baking powder and buy a new can). This is the first reaction occurring between the cream of tartar and the sodium bicarbonate.
3. After 30 seconds or so, all action will cease, and you'll end up with a still pool of chalky-looking liquid.
4. Now microwave that same liquid for about 15 seconds to bring it up to around 180°F. A second, vigorous batch of bubbling should occur, a result of the sodium aluminum sulfate. You may also notice the liquid thicken slightly—this is a side effect of the starch used to keep the baking powder dry. It absorbs water and gelatinizes, thickening your liquid as it heats.

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Now isn't that way cooler than that baking soda volcano you built for your fourth grade science fair?

The Quicker and Dirtier Guide

So after all that, we're basically left with the following short, simple explanation:

Baking soda is sodium bicarbonate. It reacts with acids immediately upon contact to produce carbon dioxide. Carbon dioxide gets trapped within batters and expands upon baking, leavening your quickbreads. Because it reacts immediately, quickbreads made with baking soda must be cooked immediately after mixing. Because of its alkalinity, it can also hasten browning reactions, adding color (and thus flavor) to things like pancakes, cookies, and muffins.

Baking powder is sodium bicarbonate mixed with a powdered acid and a starch. It does not require an external acid in order to activate. Most baking powders are "double acting," meaning they produce carbon dioxide once upon coming in contact with moisture, then again after heating. Because of this, baking powder-leavened goods are generally lighter and fluffier than those that rely on baking soda alone. This doesn't mean that you can let a baking powder batter just sit around expecting the second batch of bubbles to do all the leavening for you—the initial reaction is vitally important to the texture of your baked goods.

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With this knowledge, it should be clear that while it's possible to substitute baking powder in a recipe that calls for baking soda (use a ratio of three measures of baking powder for every measure of baking soda), you can't expect the flavor profile to remain the same with all the extra acid that baking powder adds to the mix.

On the other hand, it's quite simple to substitute baking powder with your own homemade mixture of baking soda, cornstarch, and cream of tartar. For every teaspoon of baking powder, use 1/4 teaspoon of baking soda, 1/2 teaspoon of cream of tartar, and 1/4 teaspoon of cornstarch. But do bear in mind that your homemade mixture will not be double-acting, requiring you to be extra hasty to get your pancakes on the griddle or your zucchini bread in the pan immediately after mixing the batter.

To make pancakes and waffles even quicker and easier, I like to make a large batch of pre-mixed dry ingredients, to which all I need to do is add the liquids. Breakfast on the table in ten minutes. This is a great way to fool house guests or future wives into thinking you're a really much more put-together-type-guy than you really are.

And now, if you'll excuse me, I've got a breakfast date with the dog. We've got a few dozen pancakes to down, and they aren't getting any fluffier.

You see all the exciting things I get up to when my wife is away for the week?

Continue here for Light, Fluffy Pancakes »

About the author: J. Kenji Lopez-Alt is the Chief Creative Officer of Serious Eats where he likes to explore the science of home cooking in his weekly column The Food Lab. You can follow him at @thefoodlab on Twitter, or at The Food Lab on Facebook.

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