This post may be a little lengthy but if you like flaky crust, bear with me...
Pie Crust: The Science...
Like all baking, it is a science based on specific formulas. If the formula is out of balance, the results will be inconsistent.
Three Basic Categories of Ingredients:
Pie crust is based off three basic categories of ingredients. Within each category there are multiple choices to choose. It depends on the desired outcome and use of pie crust.
1. Flour - The Beginning Place for Flaky Crusts.
Recommended: All-Purpose Flour/Pastry Flour
Yeasted bread has a texture that is created by the formation of gluten, comprised of two proteins that when mixed with water creates a stretchy elastic network that is very dense. The density of the gluten structure is necessary for the gasses of the yeast to be trapped to create a light and airy texture.
While this may be desired for bread, it is the exact opposite with cakes, muffins, & pastries; and pie crust is no exception to this rule. This is because we want a tender outcome that is less bread-like and pleasant contrast on the tongue.
To achieve this, select flour that has less protein. All-purpose flour or pastry flour works best for pie crusts. Stay away from bread flour, or high-gluten flour.
If you would like more information how flour works in baking, here is a link to an article on the subject: http://www.smacznegoablog.com/2011/03/flour-difference.html
2. Fat - The Most Important Ingredient!
There are multiple choices to use for pie crust. Recipes vary from oil, sour cream, cream cheese, lard, butter, and even goat cheese. But what to choose from?
The flaky texture in pie crust comes from a very low moisture content in the crust. Also, by selecting a fat tha has a lower moisture content will also give you more control over the dough to prevent overworking.
Based on this information either Shortening or Lard has virtually a 0% moisture content and will provide the flakiest crust on the planet! But does this make it the best choice? Not necessarily....
Shortening: has a significantly higher melting point than the other fats; between 117 degrees & 119 degrees Fahrenheit to be exact. Why is this important? Because our body temperature is 98.6 degrees Fahrenheit. This means that the shortening will not start melting in your mouth creating a crisp, but a lack of taste & texture (something we call in culinary, an "unpleasant mouthfeel")
Butter: Butter on the other hand has a melting point of 90 - 95 degrees Fahrenheit (depending on type & grade). This means it will begin to melt in your mouth when you begin to eat it. However, this creates a problem all in itself. All butter crusts sometimes seem to have a pasty consistency because of the 7-10% moisture content contained within the butter. (Yes, 7-10% is enough to create a difference between flaky & pasty.)
The solution? Use a mixture of Shortening & Butter. The BEST ratio: Substitute 16% of the Shortening with butter. By mixing the two ingredients, the moisture in the little bit of butter will evaporate in the oven. The shortening will create the flakiness while the butter will begin to melt in your mouth creating the perfect eating experience.
3. Moisture: Moisture can be really anything liquid. I've seen recipes call for vodka, apple jack, club soda, and wine. For me, I use old fashioned ice water. Seems to work best for me.
Use about 1/4 cup per 2 cups of flour in the recipe. The amount of water is going to vary slightly each time you make crust. Use just enough to gather the dough together.
Those are the three categories of ingredients that influence the flakiness of pie crust. I always add a bit of salt & sugar into my crust too. But this has nothing to do with the flakiness, just a matter of taste preference.
Two Misconceptions/Myths of Pie Crust Making:
1. Add Vinegar to the Water, It Makes it Flakier!
The vinegar does not make the dough flakier. Many people add vinegar without realizing what is really happening. Vinegar is an acid that reacts negatively to the formation of gluten. This means that it is harder to overwork your dough. The vinegar in its self does not create a flakier crust. If you don't overwork your crust in the first place, there is no need to add vinegar, it will do absolutely nothing! If you are new at making pie dough, then yes, add a teaspoon or less to the water.
2. Use a Food Processor, it's the same thing as two knives or pastry blender.
This is completely false. The science of the fat being "cut" into the flour is an important concept to the flakiness of the final product. By "cutting", you are only cutting the fat into small pieces and coating it with flour so the water will make all the fat pieces stick together. This is because fat & water will not mix, but when flour is coating the fat, the water can work with the flour to create a dough of essentially fat pieces.
What a food processor does is completely different. It forces the flour to "mix" with the fat creating a more cookie-like consistency. The difference between "mix" & "cut/coat" the fat with flour is significant. It is for this reason I recommend to only use two knives or pastry blender.
TIPS FOR BETTER PIE CRUST:
The Colder the Better: Everything should be cold when making pie dough, especially the fat. Otherwise everything will mix rather than coat. Pop the shortening, butter, water & flour in the freezer for a few minutes before starting. Using a metal bowl will also help keep everything colder longer while you make the dough. Some people even go as far as to roll the dough on a chilled marble slab; while that may be excessive, it is pretty common in bakeries where the temperature can reach over 100 degrees in the kitchen. This makes the butter in the crust begin to melt and creates a sticky mess! However, in the home kitchen is not necessary, though some will argue otherwise.
Add a Tablespoon of Sugar to Crust: Sometimes pie crust can have a slightly bitter taste. The bit of sugar will help neutralize this.
Salt is Recommended: 1/2 - 1 tsp is all that is needed. Especially if you are using vinegar in your crust, salt is a necessity. Vinegar is an acid and can create an "off" taste. Salt is alkaline and neutralizes acid making the "off" taste completely disappear.
I hope this makes sense and helps you out. Below, I've summarized the recommendations. It may sound like a lot, but it really isn't. I've just incorporated a lot of scientific reasons in the post. Take out the reasoning and you have a straight forward method of pie making. There is also a sample recipe for the perfect flaky pie dough for you to try.
Summary of Recommendations:
1. Use All-Purpose Flour or Pastry.
2. Use a Mix of Shortening & Butter. 84% Shortening, 16% Butter.
3. 1/4 cup ice water per 2 cups of flour.
1. Use Two Knives or Pastry Blender.
2. Use Cold Ingredients.
3. Toss Water with Fork into Fat/Flour Mixture.
Pie Crust RECIPE:
Makes 2 pie crusts.
2 cups All Purpose Flour
1 Tbsp. Sugar
1/2 tsp. Salt
2/3 cup Shortening, chilled
2 oz. Butter, chilled
1/4 cup Ice Water
Sift flour, sugar, & salt together. Cut butter and shortening into fat with two-knives or pastry blender until resembles coarse sand. Drizzle ice water over fat/flour crumbs. Toss with fork just until it begins to form. Gently gather the mixture together and firmly press together to form two disks. DO NOT KNEAD, just press together! Wrap with plastic wrap and chill for 20 minutes. Roll out as desired.
To Make the Top Crust Shiny & Golden Brown, as pictured, whisk one egg white with a pinch of salt and brush on with a pastry brush before putting pie in oven.