Structural analysis of a chocolate chip cookie

I probably shouldn't have baked chocolate chip cookies yesterday, what with today being one of the two biggest chocolate-buzz holidays on the American calendar. But I did.

I've had a lot of trouble figuring out the best recipe adjustments for high elevation. My cookies have a tendency to puff up big, and then collapse into goo. The end results look like this:


All wrinkled around the edges, and flat in the middle. In fact, it looks like something I could map:


Those are fold symbols for the wrinkles around the edge, and normal fault symbols for the places where the crust broke open to reveal the goo beneath.

And that got me thinking about how I would interpret this if it were, say, a radar-mapping image from another planet. The folds imply shortening perpendicular to the hinge lines - that is, the cookie seems to have shrunk. (The Small Human would be upset.) But the normal faults imply that the cookie stretched perpendicular to the cracks - the cookie grew. Weird. Inconsistent stories. Makes no sense.

But a structural geologist is not bothered by confusing, totally messed up rocks cookies. This is what we live for. The next step should be to think through some possible explanations. Are the structures all the same age, or does this mountain range cookie represent two different events, superimposed? Are the old normal faults folded? Are the folds pulled apart?

Unfortunately, in this case I don't have any good cross-cutting relationships, and the interpretation remains ambiguous. (This is where a few good zircons might save my day. Unfortunately, cookies do not contain good minerals for dating. Or maybe that should be fortunately. Zircons are hard on teeth.)

In this case, however, I know what the cookies looked like when I checked the first pan before they were ready to come out. First the cookies puffed up, and then they collapsed. While they puffed up, their surface area increased, so the cookie crust was pulled apart. When the cookies collapsed, the surface area decreased again, and the cookie crust wrinkled as the dome tried to fit itself into a pancake. (Ediacaran's trilobites have similar features, though I suspect they don't taste as good.)

My model doesn't exactly explain my structures, though. When the cookie puffed up, I would expect it to crack in radial fractures, but it doesn't - the "normal faults" are parallel to each other. I can wave my arms and say something about the local stresses being perturbed by the chips or something, but I have no real clue what was going on.

And I can't go back and look for other features to test my models. I've already eaten the cookie. It may have been an imperfect modeling medium, but I bet it tasted better than the average sandbox experiment.

More like this

My reviewers commenters on yesterday's post on chocolate chip cookie deformation had some great points. (Some of them also seem to have been very hungry. For those who want me to experiment more, and to get to analyze the results: looks like I've got something that I can promise once the Donors…
Like so many moments of culinary inspiration, this plum clafoutis is nothing like what I was thinking of prior to actually wandering into the kitchen to make dinner. I was going to make pancake dome pancakes. Pancake domes are features on Venus. They are so named because they look like pancakes:…
By USA Science & Engineering Festival Nifty Fifty Speaker Jeff Potter Jeff Potter's Patent-Violating* Chocolate Chip Cookies. Photo by Jeff Potter One of the biggest advantages that home-cooked foods have over store-bought goods is time. Commercial products have to be shelf-stable, so…
I made a promise to myself that every month, I would at least look through the abstracts on my RSS feeds and note interesting articles that I wanted to find time to read. So now it's May 30, and I'd better do it before the June issues come out. So... articles in the May issue of Geology that look…

Then again, it also underwent a bit of metamorphosis.

By Lynn David (not verified) on 12 Apr 2009 #permalink

possibly less leavening? if it's puffing up quite large, then it's rising too fast and lacks the structure to hold up after the leavening gives out. depending on the sheet pan that you are using, (insulated versus non) the cookie will cook from the edges in. the tendency for the cookie to gain the tall ridges around the edges is a sign that the edges are cooking and firming up while the middle is undercooked. when all the air drops out and the sugar cools, the center collapses. same happens with cakes and bread. at altitude the water will boil at lower temperatures and cause premature puffing...

a couple of thoughts would be to not use an insulated sheet pan. raise the pan to the top of the oven to promote cooking from the top down. use a bit less leavening (like half,)or at least slower acting. removing a spoon or two of sugar, or add a bit of flour. both will lead towards a better structure that sets faster. also, there are varying attitudes towards the shape of the cookie before cooking, if you press it flat you can promote faster cooking near the middle. some people I know insist on forming the cookies as a ball, but that probably wouldn't work for you.

good luck... see if you can actually get 60 out of the nestle recipe that's on the back of the chip bag... I've only managed it once...

How important is the metamorphism to the structure in this case? The reactions involved certainly drive off lots of volatiles (cookies are much drier than their dough!), which are then lost to the atmosphere, since the cookies aren't surrounded by confining rocks. The non-radial nature of the initial faulting may have something to do with the binding nature of the egg?

My favourite chocolate chip cookie recipie contains a fair bit of rolled oats in addition to wheat flour. In my experiance, these are *much* less likely to collapse again, because the oats provide more support for the increased volume than does the simple flour-sugar batter of your cookies (yes, I can tell you didn't use oats from the photo). However, I haven't had a chance to play with it at higher elevations. Perhaps a dedicated experiment day is in order--find a variety of recipes, with and without oats and different proportions of other ingredients (invite a bunch of the small person's friends over to help consume the extra amount made) and take notes as to what variables have which sort of structural results, and which ones taste best (not necessarily related!)

I would only expect the cookie to get radial fractures if the force was only punching up through the centre. As it is, the entire top of the cookie rises, but stops as the dough cooks. As it cooks from the edges in, it creates something more like a stepped pyramid/dome. A series of points near the edge set, but the middle keeps rising and pulls away, creating concentric stretch lines.

As a former geology student who then went on to be a professional cook, (don't ask, it made no sense then, it makes less sense now) I am glad I'm not the only person in the world who views their food as rocks. I have been known to play with bowls of flour, and tap them to get fractures and slip, build mountain ranges which I then erode with milk or egg, and watch the way stress lines occur depending on the direction I roll out shortbread or pastry. It's also fun to watch the volcanoes when you pour boiling water on jelly (jello) crystals.

I've never cooked at altitudes that affect the way things rise, but have very light hands so used to have a problem with all cookies and cakes rising to the point where they flopped. As someone else suggested, reduce the sugar content a bit, adding honey or jam to a cake mix always makes it stickier and more prone to collapse. Be more brutal with the mix. All the tips you see for getting nice light cakes and biscuits, do the opposite (eg. I NEVER sift flour). I often add almond meal (ground almonds) to cakes to give them more oomph (is that a term Americans are familiar with?), wholemeal flour does that too, but almonds are yummier - especially in self-saucing butterscotch pudding. Adding almonds also proportionally reduces the amount of raising agent. Living in Aus I use self-raising flour, so in a mix that calls for two cups of SR flour, I might use 1 1/2 cups SR flour and up to 1 cup of almond meal (it's less absorbent than flour).

The other thing that makes a big difference to the puffiness is oven temperature. Even 5 degrees Celcius can make the difference between cakes and cookies that rise nicely, and ones that rise too fast and look more like volcanoes. At that point I get both concentric and radial fractures. Another five degrees with too much air incorporated can turn a cake volcano into a caldera. OTOH too hot an oven produces cookies that are brown around the edges and gooey in the middle, and yours look pale all over, so maybe you need to increase the temperature a bit.

Looking closely at the photo, it looks like the mix was too wet and too sticky. A spoonful or two more flour would be my first plan of attack, along with kneading the dough a bit more to develop the gluten more.

By eleanora. (not verified) on 13 Apr 2009 #permalink

Actually Alton Brown did a show on CCCs and came up with three different recipes - depending on preference. They are:

The Puffy
The Chewy
The Thin

Also - the fact that the faults seem to follow the edges suggests that perhaps heat differentials (batter close to the sheet being hotter) might have something to do with the distribution. But that is pure confection convection conjecture.

best post of the day so far

I think the chips had a huge influence on the distribution and style of structural deformation ... but, I think you'll have test that by making various batches of cookies w/ varying amounts and compositions of chips. The Small Human will likely be happy about that.

Perhaps the gluten in the flour is affecting things. There is also the question of scale. The weights we are dealing with here are far less than what geologists are used to dealing with. No technical background myself but guessing these might be factors.

Obviously more experimentation is required. Multiple batches testing variations in leavening, temperature, moisture content and mixing time. To eliminate bias, mark the batches by number or letter and send them to me for testing. Always glad to help in the name of science.

How interesting. One of my geology texts used a frozen pizza as an analogy for structural geology. I wonder if there's something about structural geology that just makes people hungry.

Fun post! and yummy! But FYI, your interpretation is WRONG on this part: First the cookies puffed up, and then they collapsed. While they puffed up, their surface area increased [No, it decreased!], so the cookie crust was pulled apart. When the cookies collapsed, the surface area decreased again [No, it increased!], and the cookie crust wrinkled as the dome tried to fit itself into a pancake.

as the flat proto-cookie heats up, it expands DECREASING surface area (becoming more sphere-like, a sphere always has the least surface area of anything).

A pancake has far far more surface area exposed than a ball of dough. A 'domed' cookie is in between the two.

Lots of structural geologists confuse this, I don't know why. The way to make a sphere have more surface area than a pancake is if the sphere is hollow with a hole to the outside, like an open pot, where both the inside and outside are exposed. Right?

Ediacaran's trilobites have similar features, though I suspect they don't taste as good.

Since trilobites are related to crabs, lobsters and shrimps, they may have tasted something like them. On the other hand, they could have tasted something like chicken.

The person who said it was the flour was right. The answer to this is to add more flour to the recipe. .25-.5 cups should do it if it's a normal-size batch.

A better geo-analog might be salt collapse structures.

Been baking cookies at high altitude for decades now; and elin is correct, add flour. Also, add a bit more vanilla to balance the flavor.

Nice blog, by the way, from a fellow Colorado structural geologist.

By oblate sphereoid (not verified) on 21 Apr 2009 #permalink