Tune in to SciFri on December 12, 2014 to hear
Cooking for Geeks author Jeff Potter talk cookie science.
One of the biggest advantages that home-cooked foods have over store-bought goods is time. Commercial products have to be shelf-stable, so manufacturers have to come up with clever tricks to mimic home cooking. What if we dug into the literature and tried using those tricks for ourselves?
A freshly baked cookie—“just like Mom used to make!”—ends up being crispy on the outside and chewy in the middle. Some enterprising researchers at UC Davis proved this by building a non-magnetic oven inside of their MRI machine and then baked cookies while watching what happened to the water in the dough as it baked. (I’d love to see the grant application for that one.)
A dozen cookies and MRIs later, they had proof: The edge of the cookie definitely dries out—and to a remarkable extent—during baking. After a day or two, however, the moisture evens back out and the cookies revert to having a uniform ductile, soft texture, losing that fresh-baked quality. (And a week later, the sugars recrystallize—that’s how the cookie crumbles!) How can we prevent that?
Crispy-chewy chocolate chip cookies are incredibly hard to make, at least commercially. Luckily, patent #4,455,333—originally owned by Proctor & Gamble, and which expired more than a decade ago—has the answers. And, thankfully, it has a useful, accessible description of how to create doughs that turn out chewy or crispy.
Soft cookies have a water concentration of six percent and higher, while crispy cookies are drier. Moisture is the key variable in a soft cookie, but one can’t just add more water into a dough. The dough needs to remain relatively compact as it starts to bake, otherwise it will spread out too quickly and you’ll get flat cookies with burnt edges.
A little later on, I’ll share my recipe for making a cookie that stays chewy on the inside and crispy on the outer edges. But first, here’s a little background on what makes one cookie crispy and another chewy.
Variables for Crispy Versus Chewy Cookies
Crispy cookies are actually the easier of the two to make: Create a dough that holds less water, or bake a dough longer, and the final product will be drier. To make chewy cookies, though, you have to formulate the dough so that it holds on to more water as it bakes. Here are the common ways of doing this:
- Substitute glucose/fructose-based sugars for sucrose. In baking, as the dough heats up, the sugar dissolves into the water from eggs and butter and forms a syrup, but—and this is the key!—different types of sugars will saturate that solution at different points. Sucrose molecules, being roughly twice the size of fructose and glucose molecules, won’t create a solution with as much water, cup per cup (in other words, for a given volume of the sugar in solution at full saturation, there will be less water present). This means you can hold on to more water by using simpler sugars such as glucose or fructose. Likewise, corn syrup—the sugar in corn syrup you buy is essentially 100 percent glucose—is also a smaller sugar and will hold on to more water in baking. While crispy cookies call for lots of white sugar (sucrose), chewy cookies use more brown sugar (which is nine parts white sugar to one part molasses; the molasses has fructose and glucose).
- Add corn starch. Corn starch doesn’t dissolve in cold water, but as it heats up, it will gelatinize, glomming onto water, and preventing that water from leaving the cookie as it bakes. (There’s another patent that adds ground-up gel into the dough, yet another clever trick for chewy cookies.)
- Use bread flour.
Gluten, too, will increase chewiness, as its elastic nature means that the baked good won’t fracture and break. Using a higher-gluten flour will modestly aid, but it's not common practice for chewy dough recipes. Water from butter, when melted, will help with gluten formation. (For more about gluten in flours, check out this section
in my book, Cooking for Geeks
- In addition to making dough that holds on to water better, there’s another obvious trick to making chewier cookies: Don’t bake the cookies as long! (Chilling the dough also falls into this category.) I looked at the baking time listed for the first six recipes I found on Google for “chewy chocolate chip cookie recipe”; the average bake time was 12 minutes, 20 seconds. For “crispy chocolate chip cookie recipe”? 14 minutes, 55 seconds—a full two-and-a-half minutes longer! (The average temperatures were only a few degrees off—essentially equivalent.)
In reality, crispy-versus-chewy cookies end up being a balancing act of all these tricks, along with more subtle ones, such as tweaking the dough’s pH or, depending upon the type of cookie, including humectants such as raisins.
Sidenote: Time & Temperature
Everyone has his or her own opinion about when a cookie is done baking. When baked at 350°F, six minutes is too short (see the left-most cookie in the photo agove; you can’t even pick it up!). If baked too long (~18 minutes; right-most cookie), the cookie is beyond saving, even when dunked in milk. Somewhere in the middle is perfect. Rough rule of thumb: A 1/2-ounce cookie, at 350°F, will be gooey at 8-10 minutes, chewy at 10-12 minutes, and crispy at 12-14 minutes. But remember that the dough formulation matters, too. If your favorite cookies aren't coming out the way you like in terms of gooey-chewy-crispy, and you’re following a recipe that ought to work, the first thing to change is the time and temperature that you bake them.
How to Make Patent-Violating* Chocolate Chip Cookies
*Patent #4,455,333, which is thankfully now expired
The trick to making a shelf-stable cookie that seems fresh-baked—crispy on the outside, chewy in the middle—is to make two different doughs! Use a chewy dough for the center of the cookie and a crispy dough for the edge. Rolling these two doughs together and slicing them is a technique used in “refrigerator cookies,” where dough is rolled into a log, chilled, and then sliced. Normally this is done with multiple doughs to create cookies with visual differences—for example, those with a red colored center and a white edge. In this case, we’re using two doughs to change the texture in different regions, which in hindsight is obvious, but it’s not at all obvious at the outset.
A normal chewy dough recipe would call for more brown sugar and shorter baking times, but neither of those will work—we don’t want the center to be a darker color, and we can’t bake the crispy part longer, because, well, physics. I’m using corn syrup in this version to increase the simple sugar ratio in the chewy dough, but given the framework above, feel free to experiment!
1. “Crispy dough”: Make a batch of chocolate chip cookie dough, starting with a standard recipe, such as the Toll House® Chocolate Chip Cookie recipe. Instead of 3/4 cup white sugar and 3/4 cup brown sugar, use 1 cup white sugar and 1/2 cup brown sugar. This batch will be our “crispy” dough.
2. “Chewy dough”: Make a second batch of chocolate chip cookie dough using the same recipe. Instead of 3/4 cup white sugar and 3/4 cup brown sugar, use 1/2 cup white sugar and 1/2 cup brown sugar, and add 1/2 cup corn syrup. This dough will be the “chewy” dough. (You’ll notice that it’s also stickier and wetter. Normally this would be a problem, as a wet dough would spread out, but in this case, it’ll be surrounded by the other dough).
3. Transfer the chewy dough from the bowl onto a large sheet of parchment or wax paper, form it into a log shape about one inch in diameter, and then fold the paper over to surround the log. Roll it a few times to ensure it is round. Place in freezer and allow to chill, around 30 minutes.
4. Meanwhile, spread the crispy dough out onto another sheet of parchment or wax paper and form a large rectangle that’s the length of the chewy dough log and wide enough to wrap around the log. (You can place a second sheet of paper on top of the dough and then roll it out, if necessary.)
5. After 30 minutes—that is, once the chewy dough log has stiffened enough to be workable—place that log on top of the rectangle of crispy dough. Wrap the log with the crispy dough, joining the ends together.
6. If the conjoined doughs feel too soft to slice, place the whole log in the freezer again to chill, or let it rest overnight in the fridge. (Some people swear that resting the dough overnight matures the dough and improves the flavor—but I’ll save that for another time.)
7. When ready to bake, preheat your oven, slice the dough into cookie-sized discs, and bake per direction. I recommend using parchment paper
Note: If you don’t have corn syrup and you’re itching to try this right now, honey is a potential substitute as well: At 38 percent fructose, 31 percent glucose, it’s remarkably similar to high-fructose corn syrup in sugar composition (approximately 17 percent water and approximately seven percent maltose are the other major substances). Of course, honey will bring its own flavor and color to a cookie, but that might be interesting, depending upon the type of cookie you make. Crispy-chewy oatmeal cookies, anyone?