You know it when you see (and taste) it. Perfect pie crust. Flaky but not crumbly. Substantial enough to hold the filling but not tough. Buttery and delicious. For many, the key to a perfect crust lies in years of practice and for others, it’s all about praying to the right pie gods. Our secret pie baking power? Science.
Pie crust has one of the shortest ingredient lists: Flour + a little Salt and Sugar + Fat + Water. When flour and water come together the result is a complex network of gluten proteins. And the key to a good pie? Enough of a gluten network for the pie to hold its shape but not too much for it to become tough and chewy. Enter the wonder ingredient of fat. Many baking fats are actually a matrix of water droplets and fat. During baking this water does double duty – helping form gluten and, as it evaporates, creating air pockets that make flaky layers. Meanwhile, the fat keeps the crust from getting too tough by inhibiting the gluten connections. All of these happenings are part of the baking reaction.
The other major chemical process in pies is the Maillard reaction. In the Maillard reaction amino acids interact with reducing sugars at high temperatures (140-165oC) to produce a range of complex molecules. This reaction is the driving force behind the great tastes of everything from baking breads to grilled steaks to roasted marshmallows. In pies, the Maillard reaction is why the final crust is brown and tastes a little caramelized. It’s also responsible for the delicious aroma that comes from the oven once the pie reaches around 300oF.
In principle, these reactions are straightforward and simple. But like many chemical reactions executing them can be a little more challenging and take some practice. Here are some biochemically verified tips and tricks that can help you on your way to pie success. (Note that they’re also based on my own baking experiences. If you’ve found conflicting data please let me know!)
- Choose a Fat: There are a lot of potential pie fats out there and each has a unique melting temperature and moisture content. Butter has one of the highest moisture contents. Remember that water leads to steam leads to air pockets, so butter based pies have an edge when it comes to flakiness (a good thing in pie crusts). But butter brands also vary anywhere from 12 to 20% water so check before. Other fats like shortening, margarine, or oil can also be used, but, because they don’t have water in them, they work better if you first make a fat-water emulsion.
- Hold the Acid: Vinegar is a well-known tenderizer, and you may have heard that a splash of vinegar can help your crust. Unfortunately, adding just a small amount of vinegar creates a mildly acidic environment (pH ~6) which actually promotes gluten formation and slows the Maillard reaction. To get any real tenderizing effect you’ll need to bring the dough pH way down by adding a lot of vinegar. Yet this can make the dough too wet to work with and can also create a more sour-tasting crust.
- Try an Alcohol: Substituting alcohol for water or a mixture of alcohol and water can also help with flakiness. Most dough mixes need a bit of a liquid boost at the end to make them malleable. Alcohol, unlike water, doesn’t promote the formation of gluten. At the same time it’s important to know that most alcohols don’t burn off completely during a typical pie’s baking time. As only a tablespoon or two of liquid is used per pie the substitution won’t make you tipsy but it can add a slight taste or be an issue for guests with strict dietary restrictions.
- Amp up the Maillard Reaction: A running theme of pies is limiting proteins within the crust. On the surface, it’s a different story. The extra protein here increases the buttery brownness by providing more amino acids for the Maillard reaction. So you can increase the deliciousness of your pie by brushing on a top layer of beaten egg yolks or heavy cream.
- Pay attention to incubation times and temps: Like many experiments, cooling and heating are powerful tools in pie making. Many pie recipes require multiple chilling periods. These keep the fat in the crust from melting and prematurely releasing water. The actual amount of cooling required varies depending on the environment and the chosen fat’s melting temperature. However, a good standard operating practice is to keep all the ingredients as well as the bowl, measuring cup, and rolling pin below 70oC. Heating times also vary depending on the crust and filling type so here’s a good place to carefully follow the recipe. If you’ve ever wondered what’s happening in the oven as the pie cooks here’s a universal timeline: Fat melts and releases water @ 35-40oC (internal temperature) –> Steam forms and creates air pockets @ 100oC (internal temperature) –> Maillard reaction occurs @ 154-165oC (internal temperature).
Happy Pie Making!