The Science of Aging Meat

There is a phenomenon that frequently occurs in the world of gastronomy in which food that was once considered lowly, crude, or simple is transformed into the prized fare of the rich and well-heeled. What was once referred to as "peasant" food often finds itself, many centuries later, on the tasting menus of the world's best restaurants. Aged meat is one of those wild, ancient foods that has seen a meteoric rise in demand and price in the last century.

Aging is the controlled decomposition of meat first employed as a form of preservation. Without refrigeration, hunters and farmers would store cuts of animal flesh in cool, dark cellars or caves where molds, microbes, and enzymes would do the work of preserving the meat. A bonus to the preservation process was the meat's tendency to become more flavorful and tender through aging. Much like cheese, those early-aged meats were inoculated with strains of penicillium molds and other microbes that create the funky, umami flavor that is so highly sought-after today. It speaks to the deep memory of human genetics that what we crave most are the flavors of slight decay, something our ancestors would have known well.

Managing Decay

The aging process begins the instant an animal dies. Enzymes in the muscle tissue begin to digest long strains of glucose molecules called glycogen. The enzymatic digestion creates lactic acid within the muscle, which maintains a low pH level that is inhospitable to harmful bacteria and microbes. However, when an animal is stressed just before death, its body uses the excess glycogen stored in the muscles. It leaves nothing for enzymes to digest, creating an environment within the tissue that could allow bacterial growth. Livestock slaughterhouses will bleed animals immediately after stunning them to remove as much blood as possible from the carcass to ensure proper aging. Game animals may be more difficult to age properly due to the inevitable stress that can occur after the animal is shot and the fact that it is not feasible to bleed the animal.

Rigor mortis sets in between one and four hours after death, depending on the animal's size. Rigor occurs when calcium enters the muscle cells as they begin to fail, and the muscle filaments contract and lock in place. Hanging an animal before rigor sets in allows the muscles to remain stretched out rather than bunching into a tight ball that will be difficult to cut and unpleasant to eat. Approximately 48 hours after the onset of rigor, enzymes called calpain and cathepsins begin to break down the proteins binding the muscle filaments and dismantle connective tissues, causing rigor to cease.

The Science of Flavor and Tenderness

As the aging process progresses, enzymes inside the muscles create molecules that increase the flavor and tenderness of the meat. Proteins are broken down into amino acids, such as glutamate (also found in MSG), that we recognize as savory or umami. Glycogen is dismantled into molecules of glucose which are the sugars that create the caramelized browning on seared meat, also known as the Maillard reaction. Fats turn into aromatic fatty acids.

The length of time you can age a piece of meat depends on the type and amount of fat present in the animal. More fat will allow for extended aging due to slow moisture loss and a more significant protective barrier around the meat. Rancidity occurs as fat is broken down by oxygen and exposure to light. Minimizing those two elements is key to the aging of any meat. Unsaturated fat ages less gracefully than saturated fat, meaning that animals such as pigs, poultry, game birds, and fish are highly susceptible to fat rancidity.

During the aging process, enzymes act upon muscle first and then connective tissue. As the enzymes work, proteins are broken down, and connective tissue fibers become dismantled. This process occurs above 32 degrees and increases in activity until around120 degrees. That is why slow-cooking a piece of tough meat causes it to become fall-of-the-bone tender; enzymes become frenetic right up until the 120-degree point, speeding up the aging process in a matter of hours in your crockpot.

Proper Aging

Most failed meat-aging attempts are caused by poor temperature regulation, especially after rigor has set in. During the dry-aging process, humidity, temperature, and air circulation can make or break the finished product. The temperature should range between 34 and 40 degrees, with humidity between 70%-90%. Ensuring the meat stays above freezing but below 40 degrees allows for maximum enzyme action while keeping harmful bacteria at bay.

Bacteria need water to survive, but low humidity will cause rapid moisture loss, creating a thick membrane on the surface of the meat, potentially trapping unwanted bacteria inside the muscle. Ideally, the meat should have a thin outer crust that protects the meat and allows continued enzymatic activity while allowing water to escape. This, in turn, concentrates flavors in the meat and decreases the chance of bacterial overgrowth. Correct aging pulls moisture out of the meat and allows molds such as penicillium to grow. Penicillium molds are anti-biotic, meaning that a layer of spores on the meat will not only add flavor (they are the same molds that grow on blue cheese) but also protect against harmful bacteria (they are the same molds that Alexander Fleming used to create penicillin).

Wet-aging is a modern method made possible by the advent of vacuum seal bags. Although some meat processing facilities may only dry-age a carcass until rigor mortis has passed, wet-aging can occur once a cut of meat has been vacuum-sealed and is placed on display at the grocery store. Similar enzymatic processes occur within wet-aged meat, but it does not result in the same flavor concentration, moisture loss, or tenderness as dry-aged meat.

To Age or Not to Age

So why do we pay so much for one of the oldest foods known to humankind? Dry-aged meat is a labor of love for those who do it well and time is money. Perfectly aged steaks begin with correct cutting and cooling, starting when the animal dies on the slaughterhouse floor. A poorly split carcass or a mismanaged cooler can destroy the aging prospect of even the most perfectly marbled beef.

Aged meat also loses weight as it ages, concentrating the cost of that steak into a smaller and smaller package the longer it sits in the cooler. These labor- and cost-intensive processes create something more flavorful, tender, and valuable than un-aged meat.

The start-up costs of aging meat at home may be comparable to the most expensive dry-aged steak. Still, with time, a daring pallet, and an appetite for experimentation, it is possible to do it at home with whatever meat you have on hand.

Your best bet is to convert a refrigerator into an aging cooler. An aging-specific refrigerator will avoid flavor absorption from other foods and impede unwanted bacterial growth. Wet-aging is also an option after a carcass has been butchered into steaks and roasts. Vacuum sealers are essential to proper wet-aging as they allow moisture retention while guarding against oxygen and bacteria. If all else fails, a few days of hanging in a semi-chilled and well-ventilated garage (or cave) will still do wonders for any game animal.

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