Thanksgiving: A Scientific Look Back

Editor’s Note: This article was submitted before Thanksgiving, and would’ve been a fine read on your Turkey Day. Alas, said editor was out of town and the article is only now being published. Said editor is eternally sorry and grateful for our resident food scientist Kelley Putt’s continued patience and knowledge.

We have Norman Rockwell to thank for the image of Thanksgiving being that of a gorgeous golden brown turkey as a centerpiece on a table filled with generations of family. But when most of us list what we are thankful for, more often than not, it is the “side” dishes that take center stage in the drama that is Thanksgiving. The true beauty of the holiday, more than the shared happiness of friends and family, is the massive spread. So, let’s take a moment to consider all the co-stars in the production that is Thanksgiving dinner.

Since it’s technically Turkey Day, it seems right to start closest to the star of the show. For some, closer than we ever want to be to any star of any show. We’ll start with one of the greatest debates of my personal thanksgiving career: stuffing. Though the name alone implies an item that is forcibly put inside another item, some have questioned whether stuffing should be cooked inside or outside the bird. The scientific basis of this argument (at least that’s what it is in my family), is some pretty basic microbiology. Everyone knows that a pink slice of turkey probably isn’t good to eat. What’s not so obvious is that the same things that make you sick in that pink piece of meat can also stick around in your stuffing. In addition to contact with the raw exterior of the turkey, during cooking the stuffing inside the bird gets soaked with delicious juice streams carrying a whole lot of flavor, but also a whole lot of something else: Salmonella (not as delicious as Salmon, don’t be fooled). To ensure the complete destruction of these pathogenic bacteria, the stuffing must get up to at least 165˚F. If you’ve read my last post (Tryptophan, Turkey, and You), then you hopefully realize how disastrous this would be. Cooking a turkey to achieve an interior cavity temperature that high would most definitely result in an overcooked exterior (the part you actually want to eat). For this reason, some have chosen to prepare and serve this dish outside of the bird. Once this decision is made, the name “stuffing” loses a bit of its meaning, and “dressing” becomes more apt. Or maybe, if you live in the south, stuffing is always dressing. In that case, please disregard.

No matter if your turkey is stuffed or dressed, as time-honored tradition dictates, it should be smothered in gravy. The list of possible gravy flavors, ingredients, and preparations is endless. And everyone truly believes their gravy is the best. So to avoid adding any unnecessary drama to your family meal, let’s not get into that. But regardless of whether it’s your aunt’s secret recipe or your brother’s questionable canned contribution, the basic chemistry of all gravy is the same. Gravy is a solid (well, liquid) example of an emulsion. Simply put, an emulsion is a mixture of two things that normally wouldn’t be mixed.  Oil and water are immiscible. If you’ve ever seen an oil spill, you know what I’m talking about. They don’t mix, no matter how hard you try. Just like your parents and your brother’s newest girlfriend. Without the help of surfactants (surface acting agents), separation will always occur. But stable emulsions can be formed when surfactants disrupt the interfacial tension between oil droplets and water molecules, maintaining them in suspension. Though hopefully more tasty, you can think of your gravy as an oil spill. Usually, it includes fat (either drippings from the bird or from turkey stock), water (often more like broth), and flour. While the flour works to increase the viscosity, it’s not the only thing stabilizing the emulsion. In addition to fat, turkey is a good source of protein, a great emulsifier. As long as this emulsion holds, your gravy, from a functional standpoint, will be a success. To be considered a success in the eyes of your family and friends, however, it might require a little more than an emulsifier or two.

If gravy isn’t your thing, your turkey could alternatively be smothered in something a little sweeter. Since its invention in 1941, thousands of Americans have turned to canned cranberry sauce as the deliciously sweet complement to all things Thanksgiving. While it’s super convenient and is definitely the most socially acceptable store bought contribution to the meal, the can (in addition to your love life, career choice, and recent weight fluctuations) might (and maybe should) come into question. This is because cranberry sauce could possibly be the easiest thing to make, and it’s far more delicious when you do. Basically, it requires three ingredients: cranberries, water, and sugar. It might seem like magic that when you put these three ingredients together into a saucepan over heat, you end up with gelatinous cranberry sauce, and that’s because it kind of is magic. But the magician, unfortunately, isn’t you. It’s actually pectin, a polymer found naturally in cranberries. Polymers are long chains of repeating subunits called monomers. In the case of pectin, these monomers are α-(1,4) linked D-galacturonic acid units. In fresh cranberries (and other plants), this polymer is found in the cell walls, acting as the cement holding them together. When heated in your saucepan, these cell walls begin to break down and release pectin. As these long chain molecules leach from the cell walls, they begin to interact with other surrounding molecules like sugar and water. As more pectin is released, the polymers begin to cross-link with each other, forming a continuous three dimensional network. During this process (known as gelation) sugar and water molecules are trapped within the growing pectin network, stiffening the mixture from a solution to a gel. The longer the sauce is cooked, the more pectin is leached, and the firmer the gel. In addition to cooking time, multiple factors can influence the gelation of pectin, including temperature, pH, and sugar content. It is, therefore, fair to say that not all cranberry sauces are created equal, and that some (homemade) can be better than others (canned)*.

So, before stuffing our turkeys and then stuffing our faces this Thanksgiving, let’s all consider that to produce that idyllic Rockwellian experience it takes a lot more than a turkey on a platter. Because after all, the recipe for the perfect holiday meal calls for equal parts art and science.

* n=1, based on data collected through 24 years of Thanksgiving experience, not representative of the population as a whole. Please don’t be offended.

Categories:   Celebrations, Smarts


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