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The DCC [Dark Chocolate Chip + Sea Salt] is a cookie loved by all [well, personally, I prefer the MCC [Milk Chocolate Chunk + Sea Salt], because I think it’s a better cookie…but hey, that’s me…]. But just the other week, a first time experience with this cookie single-handedly turned someone off of Rogue Bakery cookies FOREVER. The person bought the cookies at The Hills Market, and while they loved the store, they didn’t love the cookie. This person’s experience with the DCC was so bad, that the person said they would never buy Rogue Bakery cookies ever again. I know, that’s quite sad and disappointing. But what was it that was so wrong with the cookie?

The person said there were only two chocolate chips found in each cookie.

I was crushed reading that. Then I thought, “Wait, how is that possible??” In the 3 years of baking and delivering delicious cookies, I have never had a complaint that there were less than an adequate amount of chips or ingredients in any cookie. Also, in the first year of baking, did you know that I made sure that each DCC had at least 5 chocolate chips in each cookie? I am totally not joking. I would make sure that, before each ball of dough was baked, it had five chips in it. This was back in the day, when the DCC only had one kind of chocolate chip. I then moved to having two kinds of chocolate chips in the DCC. Why the change? Because SCIENCE.

When this “chip-less cookie” complaint came in, I kept thinking of the dough making process over and over again. How would it be possible that a cookie would only have 2 chocolate chips in the whole cookie?? This was definitely a cookie statistical anomaly. It’s hard enough trying to scoop cookie dough to avoid chips; it’s a total game of chance when scooping randomly. It’s like winning the lottery, the chip-less cookie lottery. One in a million…or maybe more like one in a thousand. Still, the odds are in one’s favor of getting a cookie with chips in it.

Back to SCIENCE…why the move to two kinds of chips? Well, believe it or not, the distribution of chips in a chocolate chip cookie is not random. Far from it. You have a mixer going, with dough being mixed by the beater blade. You pour in some chips. They get mixed around randomly…or so you think. This is not the case. Even with the rotating orbital movement of the blade, things are not really being mixed as well as they could be. Ever mix something in your KitchenAid, and notice that there are ingredients stuck on the side of the bowl that don’t get mixed in? Or have you ever mixed something, and then stopped to take off the blade, and see that there are ingredients that have not mixed in, that were stuck on the blade? This shows what we’re actually doing when we’re using a mixer, and this is where SCIENCE comes into play.

Wave Motion in a Fluid a.k.a. Mixing Cookie Dough

Physics Lesson Warning! Be prepared to learn!

The dynamics of wave motion are fascinating, because what you think you see isn’t what is happening at all. Imagine a fluid, like water, and a bunch of stuff dispersed in the fluid. There are two different kinds of wave motion that we typically see in situations like this. Longitudinal waves are waves that propagate parallel to the particle displacement i.e. things go sideways. Check out this animated gif!

Animation courtesy of Dr. Dan Russell, Grad. Prog. Acoustics, Penn State.

It’s like waves coming in from the ocean, right? Well, not quite. There’s a second type of wave motion that we typically see: transverse waves. In these waves, wave propagation is transverse to particle displacement i.e. things go up and down. Look! Another animated gif!

Animation courtesy of Dr. Dan Russell, Grad. Prog. Acoustics, Penn State.

This is a wave that you would make if you took a jump rope between two people, and just started moving it up and down. You’d get these cool wave shapes on the rope.

I mentioned waves in a fluid, like water. Waves in water are actually a combination of both longitudinal and transverse waves, which is kinda freaky, if you can get your mind around it. Not only are the waves propagating parallel to particles displacement, they are also propagating perpendicular to particle displacement. What would that look like? GIF TIME!

Animation courtesy of Dr. Dan Russell, Grad. Prog. Acoustics, Penn State.

Kinda weird, huh? But it does remind you of what you see in waves at the beach, right? Now that we understand wave motion in fluids, how the hell does this relate to mixing chocolate chips into cookie dough?? In each one of these animations, keep your eye on one little dot [in the first and last animations, the dots you can look at are colored red and yellow, respectively], and pay attention to how it moves. Notice something weird? The dot doesn’t move anywhere at all. In fact, all it does is oscillate back and forth, and stays within a certain area. And this is the key to understanding wave motion. When we create waves in a fluid, all we are doing is adding energy to the fluid; the energy then propagates through the fluid, but it has little to no effect on the particles dispersed in the fluid. Think of those dots up there as chocolate chips, and the wave motion as our mixer blade spinning around and around. The energy from the mixer blade is not mixing up the chips. The chips just oscillate back and forth. Also, some chips don’t move at all [keep your eye on a dot at the bottom of the last pic]. These animations with “dots as chips” are for an idealized situation, though. All those “chips” up there are already distributed evenly in a grid-like pattern. In the real world, there are tons of other factors, like friction, for instance, but as a a physicist, I am comfortable throwing stuff out like that, so I can focus on what’s important to me. 😉

Different chips for different folks…?

So the key to having a homogenous chip mixture in your cookie dough is NOT to mix it longer. That won’t do it…well, I mean, in time, things will get mixed up okay, but increased mixing time means your dough will get warm, which means your cookies may spread more…but that’s a whole other post. As with most things you mix in your electric mixer, you have to go in, and every so often, stop the mixer, and mix it up yourself, either by scraping up the sides of the mixing bowl yourself, by hand. Then you’re adding some randomness to the mixture, which is needed to change up the regular-ness of the chip distribution that happens when using the electric mixer, because as we’ve seen above, some chips will just move back and forth.

Another thing you can do is use the fact that smaller particles in a fluid in which a wave propagates have a different displacement than larger particles in the same fluid; adding in friction forces of the things and the fluid, this would allow the particles to move to different parts of the fluid. Of course, these “particles” I speak of are chocolate chips. To combat the problem of even chip distribution [and so I didn’t have to make sure 5 chips were in each cookie], I took this approach, and combined larger, but flatter dark chocolate chips with smaller, but taller dark chocolate chips, into the dough. The displacement of the chips would be different, possibly aiding in chip distribution in the dough. And for the most part, it has worked beautifully. But then you win the lottery, and someone gets a cookie with 2 chips in it. Oops. So now what?


This idea of different sized chips to aid in a more homogenous distribution is sound, in my experience, but there is still a chance of having a bite of a cookie without a chip. To reduce this chance, I have decided to add more chips to the DCC. But not just any chips, they have to be chips of different sizes, that are dissimilar to those already used.

The DCC now has FOUR kinds of delicious dark chocolate chips, ranging in size, as you can see above. The two chips in the middle are what were originally in the DCC. I have now added the mini chips on the far right, and the larger, flatter chips on the far left. Hopefully, the addition of these chips will combat the dreaded “chip-less” cookie, and will allow for a more even distribution of chips, so you’ll at least get one of the chips in each bite.

So there you go. Four different kinds of dark chocolate chips, all in one cookie. And why? Because SCIENCE. Do you know any other cookie bakery that obsesses over problems in such an analytical way, and uses the laws of physics to combat these problems? Hells no. But if you do, let me know, because I’d like to discuss some other theories I have regarding the heat equation and convection and conduction of energy through aluminum sheet pans.

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