Thanksgiving Turkey Science – Part 1

BY: NORA IDRINA

The first time I had Thanksgiving turkey was about four years ago during my first year living and studying in America. Before that, the most exposure I got to the concept of stuffing and roasting a whole turkey was limited to what I saw on TV. Each year, as Thanksgiving rolled around, cooking shows, sitcoms, movies, even the news to some extent were filled with turkey talk. So even though Thanksgiving never was a part of my culture or upbringing, it’s always been impressed upon me that besides the act of giving thanks, the only other thing unparalleled in its importance on Thanksgiving Day is the turkey.

Because of the importance placed on making the perfect whole-roasted turkey, I’ve always been curious about how it gets done. Everyone seems to have a unique way of doing it, and everyone swears that their way is the best. Funny enough, while most folks disagree on which specific way is fool-proof, they will generally agree that cooking a perfect turkey is not easy.

To someone with limited experience, it can be daunting trying to sift through all that information to figure out what works and what doesn’t. It’s hard to tell what it is about turkey that makes certain steps necessary and its even harder to tell which steps should be prioritized. In light of this confusion, I believe having a better understanding of the science behind cooking a turkey, its components, and how they affect the way its cooked, will aide in our ability to cook a perfect turkey (:

The Composition of Meat

Turkey meat, just like any other kind of meat, consists of muscle fibers, connective tissues, and fat. The muscle fibers within the meat are composed of myosin and actin. These are thin protein filaments arranged in bundles responsible for muscle contraction, and thus, motion. These proteins denature once heated to temperatures above 120⁰ F/50⁰ C (1) and once denatured, they contribute to changes in meat color, texture, and flavor (2).

Actin and myosin within a muscle fiber (By WhySad on Flickr)

Cooking the heat-sensitive muscle fiber proteins causes them to clump together in the form of light-scattering complexes. This is why poultry breast meat starts out a translucent pale pink but eventually turns an opaque white once cooked. The clumping together of denatured muscle proteins also results in the muscle contracting, shrinking, and squeezing out water. The longer heating continues and the higher the meat temperature climbs, the more denaturation occurs resulting in more contraction, more shrinkage, and more moisture loss. Cooking at an appropriate temperature for an appropriate amount of time results in a firm and juicy piece of meat. However, cooking the meat too hot for too long increases the likelihood that it ends up dry, stringy, and chewy (2).

The connective tissues in meat are responsible for attaching the bundles of muscle fibers to bone and are composed of collagen, elastin, and reticulin. In cooking, the most important of these proteins is collagen, the main component of the connective tissue. Uncooked, collagen is too hard to even bite into but when it’s heated to about 160⁰ F/70⁰ C for long enough, the tough, indigestible collagen eventually transforms into soft and sticky gelatin (1). The formation of gelatin adds to the tenderness of the meat and improves its palatability.

 

 

 

Collagen in connective tissue surrounding muscle fibers (By 5W Infographics on Flickr)

The difficulty in cooking any kind of meat lies in determining the most suitable cooking time and temperature. Ideally, meat should be cooked in such a way to make it tender and juicy. To do so requires controlled moisture loss and controlled denaturation of muscle fibers while still converting as much collagen to gelatin as possible. The problem is simply that meat must be cooked fast at temperatures within 130-140⁰ F/55-60⁰ C to keep moisture loss and muscle fiber denaturation to a minimum. However, at the same time, to turn collagen into gelatin, meat needs to be cooked for a long time at 160⁰ F/70⁰ C or higher (2).

To prioritize one over the other is to sacrifice the overall quality and edibility of the cooked meat. So, the inevitable conclusion to this dilemma is that there is no ideal way to cook meat and the only way to gain the best possible outcome is to adjust the cooking method to the type of meat. This is where cooking whole turkey presents an additional problem beyond finding the balance in accommodating moisture loss, muscle fiber denaturation and collagen breakdown. If you’ve ever eaten the different parts of a turkey, you’ll notice it doesn’t taste the same way all the way through. The different flavors and textures in different parts of the bird are the result of turkeys being made up of two kinds of meat: white and dark.

Dark vs White Meat

At the foundational level, turkey meat is still made up of muscle fibers and connective tissues, like any other kind of meat. A closer look at the different parts of the bird reveals, though, that due to the way turkeys move when they’re alive, the build of the muscle varies in different limbs. For live turkeys, every day is essentially leg day. They don’t fly much and they don’t really need to because they have powerful legs and thighs well adapted for regular, continuous use. In other words, their primary mode of locomotion is simply walking. When they do fly, its only as a means of providing a quick burst of speed to get away from danger so their breast and wing muscles are better adapted for explosive movements (3).

The legs and thighs of the turkey consist of dark meat. These muscles move frequently and consistently, so they rely on aerobic respiration to split ATP and release energy at a slower continuous rate. They are fueled mainly by fat, which can only be metabolized with oxygen from the blood. To accommodate this necessity, the muscle fibers are well equipped with blood capillaries and mitochondria-rich myoglobin. It is because of these capillaries and myoglobin that the leg and thigh meat have its characteristic deep color and gamey flavor (3).

Additionally, since these muscles are well-exercised and well-used, the muscle fibers in turkey legs and thighs are constantly contracting to generate movement. They need to be strong and withstand regular use, so these muscles enlarge over time by generating more protein filaments and more connective tissue (2). The resulting cuts of meat from these parts of the bird are thus, not just colorful and flavorful, but also pretty tough.

Conversely, the breast and wings of the bird consist of white meat. These limbs contain muscle fibers mainly fueled by glycogen, which unlike fat, can be metabolized with or without oxygen to generate energy. Without oxygen, however, the process of breaking down glycogen to release energy creates lactic acid as a waste product. With enough use, the lactic acid accumulates in the muscle and rapidly causes fatigue. These muscles are only required for short bursts of movement, so they have no need for extra capillaries or myoglobin. Therefore, white meat is comparatively lighter in color and less flavorful than its darker counterpart. Also, unlike dark meat, the muscles in white meat experience less exertion in live turkeys, so they tend to be lower in collagen and thus, more tender.

Dark meat from turkey leg (By David Bill on Flickr)

White meat from turkey breast (By Artizone on Flickr)

 

The conflicting demands of meat composition and meat type

To achieve a perfectly cooked whole turkey seems to me, to some extent, an act of sacrifice. It is a long, laborious process that needs a lot of hard work and patience. In addition to a loss of time and sanity, sacrifices also need to be made in terms of how much collagen you can denature into gelatin before you start to dry out and overcook the muscle fibers in the meat. To recap, you need to stay within 130-140⁰ F/55-60⁰ C to minimize moisture loss and muscle fiber denaturation but you need prolonged heating above 160⁰ F/70⁰ C to turn collagen to gelatin.

If you take different kinds of meat into consideration, you also now have the additional problem of balancing cook temperatures and times for white and dark meat. Going beyond 155⁰ F/68⁰ C is a sure-fire way to end up with overcooked white meat. Dark meat, on the other hand, will be undercooked unless cooked at temperatures above 165⁰ F/73⁰ C (2). Unless you break down the turkey into separate parts and cook them according to their compositions, it is very difficult to achieve a bird that is perfectly cooked all the way through.

Problems with turkey size and shape

Furthermore, as if these two issues weren’t sufficiently intimidating, you also now have the uphill climb of getting a turkey cooked all the way through without overcooking the outside meat. The shape and size of the bird is inconvenient to say the least. A whole turkey is large and round, almost spherical, and in a hot oven, the outside of the bird would be ready much sooner than the inside. According to FSIS (USDA Food Safety and Inspection Service), turkey meat is safe to consume once the center reaches 165⁰ F/73⁰ C (4). Depending on the size of the bird, that could take a long time.

The majestic turkey: huge, round, and hard to cook (By Ashish Sharma on Pexels)

Turkeys are usually roasted around 450⁰ F/230⁰ C. As the bird sits and roasts in the oven, the heat from the oven travels down a temperature gradient from the outside of the turkey to its center. The surface of the bird benefits from the high heat and develops brown flavors via the Maillard reaction but as you wait for the inside of the turkey to catch up, the outer breast meat can end up dry and tough once cooked beyond 155⁰ F/68⁰ C (2).

The thighs and legs of the bird that are rich in dark meat and connective tissue. They need to be cooked to above 165⁰ F/73⁰ C for the muscle fibers to denature sufficiently and the connective tissue to be broken down. Without enough heat for enough time, the meat is undercooked, tough, and chewy (2). The way the bird sits in the oven further complicates matters as compared to the breast meat, the thighs and legs are relatively sheltered from the heat it sorely needs to finish cooking.

Ultimately, it seems that the best way to cook a turkey and accommodate the stringent requirements of all its different parts would be to separate the different cuts of meat and then cook them according to their respective needs. To do so, however, means giving up the magic of serving up a whole, unaltered roasted bird – the main attraction of the Thanksgiving table.

So how do you cook a whole turkey if it’s so hard to get it right?

The science behind the cooking steps

Many people successfully roast whole turkeys every year without a hitch. Many recipes online and in cookbooks provide step-by-step guides that take you through the process of turkey-roasting from start to finish. Looking through these recipes and cookbooks, you’ll notice that to achieve the perfect roast, there is no specific fool-proof method. Some say brining is key, some will tell you to baste the turkey, some suggest flipping the turkey part-way through cooking it, some say you need to “tent” the bird with aluminum foil as it roasts. The trouble is deciding which methods work best for you.

Any turkey must be cooked all the way through before you can eat it, but a good turkey needs to also be flavorful and moist. This is where steps like brining and basting come in: to offset the inevitable moisture loss that occurs as you roast a turkey to completion and to add flavor. Brining involves soaking the uncooked turkey in saltwater solution, and then waiting for the salt to enter the bird where it imparts flavor, disrupts muscle fibers and creates a region of high solute concentration so that water can travel into the bird via osmosis. This helps keep the bird moist as it cooks (5). Basting, on the other hand, involves pouring liquids (melted butter, pan drippings, broth) over the turkey as it cooks to impart flavor and to keep the meat from drying out from the high oven heat. Essentially, the liquid that’s poured onto the turkey surface evaporates and cools down the meat so that it cooks more evenly (6).

Turkey flipping and tenting with aluminum foil may not help very much with imparting flavor, but these steps are recommended to help the turkey cook evenly and to keep it from drying out as it cooks. By flipping the turkey upside down, you expose the otherwise shielded parts of the bird like the legs and thighs to more heat while allowing the typically exposed turkey breast to face away from excessive heat. The result is that the dark meat in the turkey legs and thighs get to cook more evenly while the easily overcooked white meat in the turkey breast is less likely to overcook and dry out (2). Tenting with aluminum foil is less labor-intensive since it just involves covering the turkey breast meat with foil to shield it from heat and to prevent too much browning (1).

These steps are important to help produce a Thanksgiving turkey of good quality but thanks to an overlap in the goals of each step, it’s hard to settle on which ones to choose. All the steps are recommended to prevent moisture loss, but which one would offer the most success? If a turkey has already been brined, would it be overkill to also baste it? Or should a combination of steps be used in succession? Stay tuned for the next article, where I’ll go into more detail on these different methods and how useful they really are.

References:

  1. https://phys.org/news/2005-12-cook-turkey-scientific.html
  2. http://wtf.tw/ref/mcgee.pdf
  3. http//thegood-one.com/content/uploads/2013/10/The-Science-of-Cooking-Turkey.pdf
  4. https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/poultry-preparation/lets-talk-turkey/CT_Index
  5. http://www.virtualweberbullet.com/brining.html
  6. https://www.thekitchn.com/is-it-necessary-to-baste-the-thanksgiving-turkey-102290

 

 

Science Meets Food

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1 Comment

  1. I love this article! Funny and informative. Well done!

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