LOTS and lots of cookie chemistry questions in this week. Interestingly, several people asked whether (other than losing some of the caramelly flavor notes) there are any significant consequences to using all white sugar in chocolate chip cookies instead of the standard 50-50 white sugar, dark brown sugar mix. The answer is: oh my, yes.
Ever had a chocolate chip cookie that tasted sort of, well…off? Thinking back to my days as a lad attending block parties, I ate some very nasty chocolate chip cookies indeed. Thankfully bad cookies were very rare in the neighborhood, though I can remember thinking: how can anyone mess up a simple cookie this badly? Did Mrs. Murphy put laundry detergent in these things by mistake? It took me many years before I realized what had happened — that lacking brown sugar on the afternoon of the party, Mrs. Murphy simply used all white sugar. A small thing in the broad scheme of things, but one that had disastrous consequences for her poor cookies.
We can look to the leavening reaction for a clue to what happened. Chocolate chip cookies employ baking soda to give them some of their lift (the rest comes from the creaming of the butter and sugar). Baking soda is an alkaline substance that needs an acid to react with in order to produce bubbles. But where is the acid in a chocolate chip cookie batter? Scanning down the ingredients list, it isn’t obvious. Flour? No. Butter? No. Eggs? No. Keep looking…
Give up? Why, the brown sugar of course. Molasses (the “brown” in the brown sugar) is acidic. Take it away and not only does the cookie not rise very well, the unreacted soda remains in the dough. If it simply sat there and gave the cookies a bitter aftertaste, that would be bad enough. However it doesn’t. It finds another chemical partner to dance with: the fat (butter). As all you back woods hill folk reading me today know, when you mix an alkaline (like say, lye) with animal fat and apply heat, a very interesting thing happens. Saponification is its technical term for it, a process whereby the fatty acid chains of a triglyceride molecules are broken off their glycerol “backbones” to create plain glycerol and…soap.
The same thing happens in an all-white sugar chocolate chip cookie. Not terribly appetizing as a secret ingredients goes, is it? But such are the wages of corner-cutting in the world of chemical leavening. All you crispy chocolate chip cookie lovers out there take note: you’ll want to scale back your soda relative to the amount of brown sugar you take away. If you remove all of it, make up for the lack of leavening by adding back a couple of teaspoons of baking powder. You’ll get a different cookie, but better that than a chocolate chip-flavored bar of Boraxo with your glass of milk.