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Tuesday, July 22, 2014

Cookie Hacks - Part II: Eggs and Fats

This series of "Cookie Hacks" gives an overview of some of the ways in which you can customize a recipe to make a cookie that is exactly to your liking. Crispy, chewy, dry, moist, soft or dense... it's all about knowing which levers to pull.  Time to play mad scientist in the kitchen.


Cookie Hacks - Part II

#3 - Eggs:

"An ingredient in three parts"

Eggs and flour are the structural elements in cookies - they both contain proteins that come together to give a cookie its form.

An egg can be thought of as three separate ingredient: The egg yolk, the egg white and the whole egg (sorry, not the shell). Each has a unique composition of proteins and fat which will greatly change the characteristics of your cookies. 

Why do I need to use eggs in the first place?

When it comes to kitchen staples, eggs are a sort of culinary magic. A whole egg contains a well-balanced mix of protein and fat which provides both structure and richness to a dough.  The balanced composition stands in contrast to the (nearly) protein-only characteristics of wheat flour. A dough can be made with just flour and be structurally sound, but the lack of fat makes for a lean and potentially dry end product. Eggs are the complete package.

  • Whole Egg: A whole, large egg weighs approximately 55g. Most of that weight is water, while 7g are protein and 6g are fat.
  • Egg Yolk: The yolk accounts for 1/3 of the weight of an egg, or 17g. 3g are protein and 6g are fat. As you can see, all of the fat in an egg comes from the yolk. And less than half of a yolk's weight comes from water.
  • Egg White: The white accounts for 2/3 of the weight of an egg, or 38g. 4g are protein. The rest of the weight is water. There is no fat in the egg white.

When an egg is heated, the individual proteins collide with increasing force. Eventually, the individual proteins break down and subsequently form tangled bonds with the other broken down proteins. This network of tangled protein bonds captures the liquid in the egg to form a moist solid.

Different types of proteins (there are many in an egg) break down and form bonds at different temperatures. As a result, egg whites thicken at 145 degrees Fahrenheit and become solid at 150 degrees Fahrenheit. By contrast, egg yolks thicken at 150 degrees Fahrenheit and become solid at 158 degrees Fahrenheit, because they contain less protein and some interfering fats.

Overheat an egg, and you get a curdled mess. The protein bonds become too tight and squeeze out all of the loosely held moisture. Hope you like rubbery chunks floating in water, because that's what you'll get!

The ability of eggs to become solid changes with the other ingredients in a dough - primarily the fat and sugar. More on this later, but the tangled network of protein bonds needs to be tighter/strong to hold milk and sugar in the mix. As a result, the eggs must be heated to a higher temperature. A whole egg mixed with 1 cup whole milk and 1 tbls sugar will not set until it reaches approximately 175 degrees Fahrenheit.

What happens if I bake with only egg whites?

A dough with only egg whites will have an extremely sturdy structure. Consider meringues, which are confections made by whipping egg whites and sugar into stiff peaks. The high protein content (and complete absence of fat) actually makes it possible for egg whites to form a semi-solid through whipping alone. But anyone who has eaten a meringue knows that they are crispy and flaky to an extreme. The absence of fat means there's no tenderness whatsoever.

Cookie Hack: Increasing the amount of egg whites in a dough will improve a cookie's structure, but without the addition of some form of fat, the cookie will not be tender.

What happens if I use only egg yolks?

The yolk is more balanced with a near 2:1 ratio of fat and protein. As a result, a dough with just egg yolks will be tender and modestly structurally sound. Consider a jiggly (yes, jiggly) custard or flan. It can barely hold its form outside of a mold. However, when combined with flour, greater structural integrity is possible.

Cookie Hack: Increasing the amount of egg yolk in a dough will improve a cookie's tenderness.

Rarely will a recipe call for only egg whites or only egg yolks. More often, whole eggs are used, and then the mix is supplemented by one or two egg whites or egg yolks to swing the balance more towards structure or tenderness. 

Raw Egg and Shell

#4 - Fat:

"Butter & beyond"

So flour and eggs have created a structurally sound cookie... but too much structure can be a bad thing. A good cookie should be tender too. 

Fats help tenderize a cookie by interfering with protein bond formation (it prevents the formation of gluten bonds in flour). Fats also bring a welcomed richness to a dough. The challenge is introducing the right amount of fat to achieve the desired tenderness without destroying the structure. Ah, the baking balancing act!

Which fat is best?

Let's face it - as a species, we know our fats... we know them really well. In baking, there are three common options.

  • Butter: It's admittedly a personal bias, but I think butter is the god of fats. At 80% fat, butter is sufficiently fat-dense while also containing flavor-enhancing milk solids. Unlike other fats, a good butter not only enhances the texture, but also the flavor, of a dough. One word of caution - only use unsalted butter... you should be in control of your recipe's salt content    
  • Shortening: Shortening has a much higher melting point than butter. Adding shortening to a dough results in cookies that "spread" less when baked. And while most shortening is without flavor, butter-flavored varieties do exist. Then why use butter instead of butter-flavored shortening? While the higher melting point of shortening reduces spread, that melting point is higher than our internal body temperature of 98.6 degrees Fahrenheit. As a result, shortening does not melt in the mouth and cookies and frosting made with shortening can leave a greasy mouth feel
  • Oil: Oil is rarely used as the fat of choice in cookies because it is extremely disruptive to the formation of protein bonds and, while it results in amazingly tender baked-goods, the structural integrity is very hard to maintain. When using oil, it's important to use neutral flavored options (canola, corn, vegetable). Fats are very good at carrying flavor in cookies, so the strong flavor of olive oil or, if you're crazy, white truffle oil, would be very noticeable if used (although this may be intentional).

Cookie Hack: Increase the amount of fat in a recipe to improve the richness and tenderness of the cookie. Consider using shortening to increase the melting point of the fat and reduce "spread". Use oils to create extremely tender (potentially too tender) cookies.

Fats: Butter, Shortening, Margarine and Oil

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