Sciencegeist: #FoodChem Thanksgiving Blogging Carnival

Originally posted November 16, 2012

Thanks to the CENtral Science blogging crew for putting this together! Rachel has been aggregating the incoming links. Go and have a read. Some great stuff here!

Thanksgiving is meant to be a time of gratitude. It is a day set aside to remember all that we have been blessed with and all that we are grateful for. Thanksgiving is a time to celebrate the season’s harvests, a time to recall the first harvest of the original European settlers to America.

Well, that’s what Thanksgiving is supposed to be.

What Thanksgiving is, however, is something entirely different. It is a day when we pretend to care about the Detroit Lions and Dallas Cowboys. It is a day when we remember just how much we dislike our relatives’ politics. It is a day when you drink one too many high balls and your grandfather starts making boilermakers with Canadian Club and Bud Light. And, it is a day of overeating.

When we sit down to lunch/dinner/leftovers, we are committing ourselves and confirming our faith in the glory of starch. Mashed potatoes. Sweet potatoes. Stuffing. Gravy. Corn. Dinner rolls. Cranberry sauce. Pumpkin pie. Our communal platters are awash in starch. We are bathed in its glory. And we pray that we never again have to succumb to Dr. Atkins and his damned diet.

Thanksgiving is a holiday because it is the one day where we don’t have to believe that starch is evil. Sure, it makes us sleepy (its seriously not the tryptophan). Sure, we put on some weight (but our bodies are just preparing themselves for winter, right?).

So let’s take a closer look at the chemistry behind our true national obsession. Starch is a really long molecule. Starch is a really long molecule that is made out of a single, small molecule that repeats itself, hand-in-hand, over a thousand times. That single small molecule is glucose. You all know glucose, it is sweet and delightful and makes our world a better place.

Now, if you take one glucose molecule and attach it to a second molecule and repeat this process a thousand times, you get one giant starch molecule.

Surely you’ve noticed that starch, itself, is not pleasant to eat. In my home, the cornstarch resides in a clear container right next to another clear container that stores our powdered sugar. (Genius, right?) The two powders may look similar, but their tastes are entirely different. And potatoes, which are called pomme du terre (apple of the earth) in french, are mostly just big balls of starch. (You won’t be catching me eating a potato like an apple any time soon).

How is it that this unpleasing molecule plays such a big role in the food that we eat? And, why are these foods so enjoyable?

It turns out that starch doesn’t just hang around on its own. Many molecules of starch cluster together and hang out in “crystals”. One way to think about a starch crystal is to imagine a sheet of paper. Take that sheet of paper and cut it into very skinny strips. (Each of those strips represents a single starch molecule). Now take those strips and crumple them up into a ball. This is what a starch crystal looks like.

As you know, starch, in its resting state, is “tough”. It feels a little bit gritty in your mouth. (Again, think of corn starch or a raw potato.) What happens to that starch crystal as you cook it constitutes one of the most important transitions in cooking.

As you start to heat a starch crystal in water, the molecules of water begin to seep into the interior of the crystal and it swells. As it continues to swell, individual chains of starch start to leach out of the crystal and into solution. This process proceeds until a molecular mesh is created within the water. When you are cooking with starch, this is what you are going for. Gelation. You want your starch crystals to swell, leach some of their contents, and mesh. This “softens” the starch and makes the liquid feel “thicker”. Of course, this process can be carried out for too long of a time and the starch crystals deflate. If this happens, all of the hard work you have been putting into cooking your starch will be destroyed.

All of this is particularly important when making gravy. When preparing gravy, you have two basic starch sources that you can use. Wheat starch (aka flour) and Vegetable starch (aka corn starch or potato starch or other). There are some differences between the gravies made with these. Corn starch gravy tends to have a more clear appearance and is less likely to clump. Gravies made with flour tend to have a richer flavor, are more cloudy in appearance, and have a greater tendency to clump. However, there are several methods that you can take such that you don’t make clumpy gravy. 1) Mix your starch in cold water before adding it to the drippings from the roasted turkey. Then add the liquid slowly to the hot drippings. In the case of flour, adding it too quickly to the hot liquid causes gluten formation (think bread) and the formation of clumps. Adding the starch slowly to the pan keeps the starch crystals dispersed in the gravy. 2) Coat the starch in oil (clarified butter) before adding it to the hot drippings. The coating of oil controls the swelling of the starch crystal. It keeps it from rupturing. It also adds a deeper flavor to your gravy.

In preparation of next weekend, I may have to cut back on my starch consumption. I am fully planning to be taken in by the magic of Thanksgiving dinner and the glory of starch. I do this in full knowledge that when the clock turns midnight next Thursday and the spell is broken, I will most likely turn into a potato.