Baking Science III – Baking Soda & Baking Powder

I remember once asking my mother what the difference was between baking soda and baking powder (in my head, I knew it was that one was used for making volcanoes and the other one wasn’t).  She was busy and distractedly told me that baking powder had baking soda in it and a bunch of other things, including salt. My mind skipped right over the “bunch of other things” and latched onto “salt”.  So for years, I thought that baking powder was simply baking soda with salt (and maybe some other, non-important stuff) in it.  This is completely wrong.

Recently, I decided to take a closer look at baking soda and baking powder since I began to suspect the difference hinged on a little more than just the presence/absence of salt.  Turns out, salt doesn’t even play a role in the matter.

I. Anatomy:

BAKING SODA – made of pure sodium bicarbonate.  It reacts chemically with acidic ingredients (ex. chocolate, honey, molasses, buttermilk, etc.) to produce carbon dioxide bubbles.  These bubbles expand during the baking process, creating a leavening effect.  Because baking soda is alkaline, it speeds up the Maillard reaction (the browning that occurs when you bake/cook/burn something) and can add a nice touch of color to your pastries.

BAKING POWDER – made from sodium bicarbonate, starch (a drying agent), and cream of tartar (an acidifying agent).  It can also contain sodium aluminum sulfate, another dry acid.  Cornstarch helps prevent clumping, keeps the sodium bicarbonate and cream of tartar dry (to prevent them from reacting in the container), and bulks up the powder to facilitate measuring/standardization.  There are two main types of baking powder: single-acting and double-acting.

Single-acting powder is set off by moisture (so reactions occur immediately).  They differ based on the acids they include.  Tartrate baking powders contain cream of tartar and tartaric acid; they react quickly with liquids, so batter containing them must be cooked immediately. Phosphate baking powders contain calcium phosphate or disodium pyrophosphate; they react a little slower, but most of the reaction still takes place before heating in the oven and should be cooked quickly.  SAS baking powders contain sodium aluminum sulfate; they react little until heated, but have a bitter taste.  SAS is often used in double-acting powders.

Double-acting powder reacts to moisture, also, but most of the reaction takes place during baking.  The first reaction creates the initial bubbles, which are trapped while the dough cooks and forms solid structure during baking.  Double-acting powder contains a dry acid as well as sodium bicarbonate (baking soda) which reacts when the powder comes into contact with liquid.

II. Baking:

Whether a recipe calls for baking soda or baking powder depends on the other ingredients.  Since baking soda is basic, it won’t react and leaven the dough unless it is combined with an acid ingredient.  It will also create a bitter taste unless countered by an acidic ingredient.  When combined with cocoa powder, it causes reddening.  Baking soda is commonly used in cookie recipes. Baking powder is used when there is no acidic ingredient or in combination with neutral ingredients (ie. milk).  Baking powder is commonly used in cakes and biscuit recipes.

If you have too much baking soda, you’ll get an end result with a soapy taste and a coarse, open crumb.

If you have too much baking powder, you’ll get a bitter tasting batter that will rise and collapse quickly (since the carbon dioxide bubbles become too big, they break and the dough falls).  The end result will have a coarse, fragile crumb and a fallen center.  Too little baking powder gives a flat, tough final product with a compact, dense crumb.

III. Substitutions:

Baking powder –> Baking soda: Unless you find a way of separating the sodium bicarbonate from the dry acid and starch, this substitution doesn’t work.

Baking soda –> Baking powder: Combine 1/4 of the amount baking soda called for in the recipe with an equal measure of cornstarch and twice as much cream of tartar.  It’s not a perfect substitution, however, and taste/texture may be affected.

*Generally, it’s best to keep your pantry stocked with both baking soda and baking powder

IV. Tips:

Baking soda reacts immediately, so bake recipes calling for it right away (or they’ll collapse and flatten).

Bake recipes calling for single-acting baking powder as soon as possible (or they’ll collapse and flatten).

Even though double-acting baking powder reacts twice, the initial liquid reaction is vital to your finished product (so bake right away, or your pastries will — what’s that? Yes, that’s right, collapse and flatten.  Well, not really, but you can’t rely on the second reaction alone to do all your leavening)

*There is yet another type of leavening agent similar to baking soda and baking powder: ammonium bicarbonate/carbonate.  Recipes that need a quick rise before the dough spreads in the oven (ie. cream puffs, some cookies, and eclairs) need the fast rate gas release provided by ammonium bicarbonate/carbonate.  However, ammonium bicarbonate/carbonate aren’t usually used in household cooking since they don’t store well and lose their reacting ability quickly. 


Baking Science I – The Egg

I remember when I was a little girl and just learning to bake with my Mom, how magical it was that you could put a bunch of ingredients into a bowl, mix them, bake it, and have the whole thing turn into a cake.  As I grew a little older, I stopped wanting the magic and I started wanting the science.  I wanted to know why butter melts as it grows warmer, but an egg turns solid as it gets hotter.  I wanted to know why you put flour into a cake when it always makes the batter taste worse and why my randomly dumping ingredients together never produced a tasty result.  Recently, I’ve started researching the science behind baking and it’s been incredibly illuminating.  Baking is not a mysterious magic trick, but a fantastically precise art.  Learning these basics has transformed baking into a wonderful sort of edible alchemy.

For the first section, I wanted to start with the ingredient I was first, and most, curious about: the egg.

I.  The Anatomy

So, everyone knows an egg has two parts: yolk and egg white (and there’s also the shell, of course).  But that’s not really true.  An egg is far more complex than you may think.  There is a yolk, an egg white, and a shell, but there’s also a chalaza, middle albumen, vitelline membrane, nucleus of pander, germinal disk, yellow yolk, white yolk, air cell, and several more.  Prepare to get science-y.

There is a really great (and very in-depth) article on the anatomy of the egg, but here’s the quick summary:

Albumen (aka Egg White) – provides additional nutrients for the embryo.  It’s an excellent source of riboflavin and protein.  Egg whites are composed overwhelmingly of water, with the rest made up of proteins.  They contain little to no fat nor carbohydrates.  Since they contain so much protein, it is possible to whip them into a stiff foam by breaking and releasing the proteins (more on cooking foams later).

Chalaza – this is the thick, twisted, white mass found in the egg white.  It helps keep the yolk centered and is a good indicator of freshness; the more twisted the chalaza, the fresher the egg.

Yolk – feeds the developing embryo.  Some of you may not know this, but yolks are an excellent source of vitamins and minerals (including vitamins A, D, E, and K).  The yolk also contains a fair amount of protein.  However, the yolk is where all of the egg’s fat and cholesterol can be found.  According to the USDA, one standard egg yolk contains an average of 210mg cholesterol and 4.5g of fat.  It also contains an emulsifier, lecithin, which helps thicken and bind non-combining ingredients (like oil and water).

Air Cell – forms when the insides of an egg contract as they cool after being laid.  Air cell size is used to grade eggs; the smaller the air cell, the fresher the egg.

II. Baking:

If you have baked, you have probably baked with eggs.  But, if you’re like me, you didn’t know exactly what those eggs did.  I understood that egg whites make something fluffier and egg yolks make it moister, but I didn’t know how or why.  Now I do, and here’s a brief explanation of how it works:

Eggs are often used as binding agents in cooking (due to the function of lecithin as an emulsifier).  They can be used to make the consistency of a mixture more even and help ingredients like fats and water combine smoothly.  Egg whites are used as leavening agents; when heated, the proteins inside break open and expand, causing the pastry to rise.  However, they also push out moisture, which can leave the pastry dry.  You can also break open and release the proteins by beating or whipping the egg whites, which creates a foam and can be used to add airiness to a pastry.  Egg yolks are used to moisten and combine baked goods; they add richness help create a smooth texture.  Egg yolks can leave your pastry too wet, however, if the correct proportions are not used.

III. Tips:

Peeling Eggs – to more easily peel boiled eggs, run them under cold water and start peeling from the air pocket

Preventing Eggs from Cracking – to prevent eggs from cracking while boiling, prick a small hole in the air pocket. Eggs crack because the air becomes heated, expands, and pushes at the shell, cracking it.  You can also let the eggs come to room temperature and, most importantly, place them in the water before you turn on the heat; do not place eggs straight into boiling water.

Judging Freshness – heavier, fuller eggs are fresher because, as eggs age, water evaporates through their porous shell.  Therefore, in water, an old egg stands on end, a rotten one floats, and a fresh egg sinks. A small air chamber is another sign of a fresh egg; to test, hold an egg up to the light and look for the air cell.  When cracked, the egg white should be thick, solid, and slightly cloudy.

Whipping Eggs – when whipping eggs into a foam, make sure to start with room temperature eggs.  This makes it easier to release the proteins and helps them create a stronger structure.