This, however, is a blog about science, so I want to talk about the science behind éclairs. The dough is very simple to make. First water, butter, and milk are brought to a boil, then flour is stirred in all at once. The dough that forms is stirred and cooked for a few minutes on the stove to swell the starch. Then you transfer the dough to a mixer bowl and eggs are beaten in, one at a time. The dough is piped onto cookie sheets and baked in a hot oven.
You notice that there is no chemical leavening agent included in the dough, such as yeast or baking soda, and yet it forms lots of wonderful air pockets during baking. How does this happen? Steam forms as the puffs bake and the strong gluten structure formed by beating the dough stretches to hold the steam. With the steam trapped, the heat then coagulates the gluten and egg proteins forming a rigid wall that will hold its shape. If done properly, the puffs will be golden brown, with a hollow center crisscrossed by a soft network of dough filaments.
Each ingredient plays a part in making a good puff. First the water, milk, and butter need to be boiling so that when the flour is added it will swell (hydrate) the starch granules and gluten (gluten is made up of two proteins gliadin and glutenin). The more butter you add, the more tender the cream puff will be, but if you have too much it will interfere with the gluten stretching and the cream puff will collapse.
The eggs that are beaten into the dough act as the leavening agent. The yolks add fat and act as an emulsifier for a smooth and even texture in the finished product. Egg proteins add to the structure of the cream puff as it cooks.
Baking any dough is a delicate dance between two processes: the expanding of gas and the coagulation of gluten and gelatinization of starch. If the oven temperature is too low, the trapped air will expand and escape before the gluten and starch have set. The puff will collapse and be a tough mass. Also, the puffs depend on steam production to cause the to rise: if the temperature is too low there won't be enough steam to cause the puff to rise, and if the temperature is too high, the proteins and starch will set and brown before the gas has expanded to its full size. This will again lead to unpuffed puffs.
This recipe was an exciting start to our membership in the Daring Bakers Club. I felt like many of the components were unnecessarily complicated--for example, the best glaze for eclairs I've ever tasted (and had great success with) is a simple 5/4 chocolate/cream ganache. It doesn't get any easier than making it in the microwave. The glaze recipe we were instructed to follow to the letter never set up, not even after time spent in the cool of our freezer for a while. It included silly component recipes (which tasted great as ice cream toppings) but did nothing to further our desire to repeat this recipe experience. The choux recipe chosen for us by this month's host was a good one, although many important instructions were omitted from the instructions--like how wide the puffs should have been in addition to how long, and whether they should cool on racks or on sheets or on parchment paper pulled off the sheets and placed on a counter/table. Dave complained that it seemed like this recipe was intended to dirty as many dishes as possible, and because he is our "dishwasher," he should know. We thought the double chocolate hit from the pastry cream and the glaze would be too much (even for confirmed chocolate lovers), so we opted for a hazelnut pastry cream that we created from our vast store of experience making hazelnut gelato and it turned out really nice. We WILL be making that part again. All in all, this was supposed to get us cooking together in the kitchen, which happened three nights in a row this week for us to get all our components together. So, in that way, despite my quibbling, it was an unqualified success! ---Dave's lab assistant
