What is the process and what are the benefits?
The process of transforming muscle from a cow into prime meat on a plate starts at slaughter. In addition to not being humane, it is known that stressing any animal before slaughter degrades the quality of the meat produced. After a humane slaughter, muscle continues to live on for a little while by consuming energy stores (glycogen) in the muscle. This produces lactic acid that controls rampant enzyme activity, reduces microbial spoilage, and retains moisture. However, if an animal is stressed its metabolic rate increases and it starts to consume the energy stores while still alive, meaning these post-slaughter processes don’t occur. Meat Standards Australia assigns a very high score to slaughter in its grading system (a score of 5, compared to scores in steps of 0.15 for marbling — scientific studies indicate that marbling does not contribute as much to eating quality as is generally assumed).
Rigor mortis sets in when the muscles have completely depleted their energy stores (it takes about 2 hours in beef). As the muscle shuts down, it triggers a contraction of muscle fibres that then lock together stiffly. The beef is hung during this stage to minimise contractions by stretching under gravity.
The beginning of the ageing process occurs when muscle enzymes have had sufficient time to start to break down the tight bonds between muscle filaments, softening what is now becoming meat (after ~1 day).
After this, it will continue to age and improve during the time it takes to get to market, however this is an incidental ageing of a few days to a week, which actually is about right for poultry, pork and lamb because their fats tend to rancidity. But beef is an exception, it has been known for a long time that deliberately continuing the ageing process can improve the eating experience, and in earlier times beef was routinely aged for longer.
The dry-ageing method is the gold standard. Meat is hung for at least a month in refrigerated conditions (to stop microbial growth), with high humidity (to minimize water loss), and under ultra-violet light (to kill surface contaminants). During this time enzymes, without their normal control systems, start breaking everything apart — proteins into savoury amino acids, fats into flavoursome fatty acids, glycogen into sweet glucose and more. They also increase tenderness by continuing to weakening the bonding between muscle fibres and to some extent collagen fibres.
The down-side is that the meat will dehydrate and shrink (even in the humid environment), and usually the surface of the meat will need to be trimmed off. It becomes more expensive per kg, and holding the beef back from sale for a month under these conditions adds further cost. For these reasons, in modern times it is rarely done, and I have never had the opportunity to consume a piece of dry-aged beef. The complexity of the process means that it is not something that could be replicated safely in a domestic kitchen.
However, it is possible to wet-age beef at home for a shorter period of time and still benefit from some additional enzymatic activity. The process can be combined with flavouring and brining quite neatly in a method suggested by the Modernist Cuisine team. For each 100g of meat, brush with 3g of Asian fish sauce (I use the Red Boat brand). Wrap the meat tightly, ideally in a ziplock bag using the water-displacement method (almost completely seal the ziplock, but keep a bit open with a finger or a straw, slide the bag into water to displace the air, then seal). Keep refrigerated for 3 days. After this time there’s no residual fish-sauce taste (in fact I thought it seemed a little smokey), and the saltiness of the sauce has lightly brined the meat.
Enzyme activity is also relevant during cooking, as activity will continue and accelerate up to temperatures of around 40–50C. The longer the meat interior takes to reach doneness, the more this accelerated ageing can occur.
“On food and cooking”, H McGee, Scribner.