The Mythical (Mystical?) Pie Crust Post

And I thought I spent a ridiculous amount of time researching pie crusts two weeks ago

As it turns out, I was capable of spending many more hours since.  I've finally had to commit myself to refraining from reading any more about it starting... now.  I fear that I'm on the verge of making this my full-time job.  Whether my co-workers liked the crust or not, I somehow doubt that they'd cover for me if I stopped actually doing anything related to my real job and instead spent my workdays ruminating on the essential components of a tender, flaky pie crust.  Then again, they might argue that I don't really accomplish anything of value during most workdays anyway.  Perhaps my greatest contribution is pie crust after all.  The jury is officially out.

I'd hate for any other aspiring pie crust makers to suffer through the same fate that I've experienced the past few weeks -- pie crust just can't be this difficult.  If, in addition, said aspirants have chosen to torture themselves by reading this blog, I can only convey to you my deepest condolences.  As an attempt at reconciliation, here's my layman's summary of the prevailing wisdom regarding making a great pie crust.  Read at your own risk, this post should be riddled with the usual disclaimers about varying results and no implications of responsibility.

Pie Crust Chemistry 101

There seems to be some agreement that there are three quantifiable aspects of a good (or bad, I suppose) pie crust.

• Taste
  
• Tenderness
  
• Flakiness
  

There are likewise three major components of a pie crust, that can effect the above three aspects.  

• Flour
  
• Fat
  
• Liquid
  

The proportion (as well as the specific characteristics) of the above components, along with the manner in which they're introduced to the final mixture, determine how the finished crust scores on the preceding aspects.  By specific characteristics, I mean that there are many types of the major components that could be used in a recipe.  A non-scientific (and undoubtedly wildly incomplete) list of some possible ingredients in each of those categories is:

Flour

Cake Flour

Pastry Flour

All-Purpose Flour

Fat

Butter

Vegetable shortening

Lard

Oil

Liquid

Water

Milk

Vinegar

Ethanol (ethyl alcohol)

Each of the aforementioned aspects can be influenced by the ingredient choices and incorporation methods that the artist1 makes.  The influence is fairly obvious for an aspect like taste.  For example, it makes some kind of intuitive sense that a crust of all-purpose flour, oil and vinegar might not taste the best for the banana creme pie that you're planning.  To understand how the other aspects are affected is much less obvious -- at least to me -- and much more of a chemistry experiment.  Once those impacts are understood, however, the grass is suddenly greener, the skies bluer and pie crusts so much more delicious.

Creating the perfect tender, flaky crust is generally about controlling gluten formation.  It isn't about preventing gluten formation completely, as it's important for structure, but about allowing just the right amount to form.  

The chemistry lesson of pie crust comes in two parts.

Part 1 (tenderness)

1. Gluten provides a crust with two characteristics, strength and elasticity.  Obviously those are both important, but if too much gluten is allowed to form elastic and strong becomes hard and tough (choose your own adjectives).
   
2. Gluten = flour protein + water
   

Part 2 (flakiness)

1. A flaky pie crust requires that pockets of air are formed in the cooked crust.
   
2. Pockets of fat in the unbaked crust will melt as the crust bakes.  Using fat components with varying melting temperatures can cause this process to occur over a longer time and yield increased flakiness.
   

From what I have read, and from my limited experience thus far, you don't get the second part without a reasonable degree of the first.  So, I think that controlling gluten formation is vital, and the real key, to a good crust.  The third aspect of a good crust is simply attained through using the crust components that either taste the best or inhibit flavors in the other components from dominating the overall taste.  In general, I think that fat choices in constructing a crust influence the flavor the most, although I'm sure there are ways around that.  Also, I'm sure that there's some interesting chemistry to creating a great flavor, but I haven't done any research into it and so am not focusing on that here.

Since I think that attaining flakiness is a more straightforward aspect of a pie crust than is tenderness (at least as I've defined them here), I'll put forward some thoughts on flaky crust here, and then finish with the gluten formation information.

Flakiness

Flaky pie crust is the result of intermingled layers of fat and flour in the unbaked crust.  Creating these layers allows the fat to melt away, leaving flour layers with air pockets in between (i.e. flaky crust).  There are any number of ways that this layering can be attained and many/most recipes will allude to one or more of them, although few explain just why you're doing a particular step or using a particular technique.  As far as I can tell, instructions referring to the following are all related to flaky/layered crust:

1. Use more than one fat:  since lard, shortening, and butter melt at varying temperatures, the time-delayed nature of their melting can lead to more air pockets and a flakier crust.  To most people's palate, butter provides the best taste of the three and so is generally used in combination with one of the other two.  This is not the case in all recipes or for all people, but seems to generally be true. 
   
2. Use cold ingredients:  most recipes will recommend using cold fat, flour, and/or liquid.  Using cold flour and water prevents the fat from melting during crust preparation.  If the fat melts, then the flour will absorb that fat, rather than it being left for layers as described above.  Using cold fat likewise slows the breakdown of the fat components so that when the crust is actually rolled out there are still pockets of fat in the dough.  Again, this results in layers and flakiness in the finished, baked crust.
   

The above instructions appear in many recipes and as far as I'm concerned make sense from a pseudo-scientific perspective.  Now for the interesting stuff...

Tenderness (Gluten control)

As was noted earlier, gluten forms when flour protein is combined with water.  Basically, as more more of each is combined with the other the resulting dough becomes more structured and elastic.  This is the desired effect for bread, for instance, where you want a great deal of structure, the dough to rise (with the assistance of yeast), all that jazz.

For a pie crust, however, the goal is to create enough gluten to give the crust some structure and strength, but not so much that it gets tough and hard when baked.  So, to really make a fool of myself, here's a reasonably comprehensive list of ways that gluten production can be regulated when making a basic pie crust.  Notice that the following items can be related pretty closely to the original proposition that ingredient choices and incorporation methods can be tied to the chemical reactions that when a pie crust is created and baked.

Ways that gluten formation can be controlled

• Use flour with lower glutenin and gliadin (the major wheat proteins) content.  
• Different flour types have varying amounts of the above proteins available for gluten formation.  From least to most...
  

1. cake flour
   
2. pastry flour
   
3. all-purpose flour
   
4. bread flour
   
• Most recipes call for all-purpose flour, although some specify pastry flour.  Using a lower-content flour produces less gluten.

• Limit the total amount of water in the dough
  
• weighing dry ingredients instead of measuring makes adding the correct amount of liquid easier (measured flour can be quite inaccurate due to packing)
  
• use as little water as possible, while still creating dough that can be rolled into a usable crust
  
• Limit water exposure to proteins
  
• Coat the flour with a portion of the fat prior to adding water.  This partially water-proofs some of the wheat protein and prevents it from forming gluten when the water is introduced.  Aggressive working of the fat and flour prior to the introduction of water will not result in a tough end product.  
• Use a liquid other than water
• Ethanol (ethyl alcohol) provides moisture to the crust, but does NOT promote gluten formation, so
• Vodka2 (only 60% H2O), or
• Vinegar (most forms are fermented ethanol, but obviously taste must be taken into consideration)
  are options to use with or instead of water.
• Handle the mixture as little as possible once the liquid has been introduced.
• Minimize mixing time
• Refrigerate the finished dough prior to rolling, mainly so that you are better able to...
  
• Roll the crust only one time.  Rolling a second time will cause increased gluten formation.

In Summary...

Having written all of that over the course of a disturbing number of sessions, I'm starting to wonder if it shouldn't have just said...

Follow this recipe, shut up and don't ask questions.  (Chris Kimball, of course, is the snobby foodie from America's Test Kitchen.  As Christina noted, you can't go wrong with American's Test Kitchen).

1) the way that some pie crust snobs drone on, you'd think there was some kind of art to it, so artists it is...

2) there is some debate regarding whether or not the alcohol "burns" off when cooked.  As far as I have been able to find, it does not completely burn off, although the amount of alcohol that still remains in the crust is extremely small.