By Eben van Tonder, 18 July 2025

Introduction

Why does marbling even happen, and what changes when cattle experience stress? We have been examining the effects of stress on animals and, by extension, the human body. In this article, we go deeper, expanding the discussion to include how cortisol, adrenaline, and insulin influence fat distribution and the type of fat that forms. We trace the journey of a glucose molecule from its creation in plants through its transformation in both stressed and unstressed bodies. This piece combines scientific explanation with practical implications, exploring fat distribution, oxidative stability, sensory quality, health relevance, and the hormonal mechanisms behind it all.

1. Why Does Marbling Happen?

Marbled meat is something that everybody talks about. We know what it looks like, but why does it happen? Marbling refers to the fine strands of intramuscular fat deposited within the muscle fibres. This occurs when the animal is in a calm, well-fed state, with sufficient insulin activity to promote fat storage inside muscle tissue rather than between muscle groups or under the skin. It represents a long-term energy reserve placed deep within the muscle structure, and its formation is regulated by a balance of hormonal signals, genetic predisposition, and nutritional status. Let’s look at this in more detail.

Glucose, Insulin and the Formation of Fat: A Journey from Carbohydrates to Fat Depots

Glucose is produced by plants through the process of photosynthesis, a remarkable biochemical reaction where carbon dioxide from the air and water from the soil are combined using energy from sunlight. The outcome is glucose, a simple sugar that forms the basis of what we collectively call carbohydrates. The word “carbohydrate” comes from the terms carbon and hydrate, referring to its molecular composition of carbon, hydrogen and oxygen.

We consume these carbohydrates mainly through grains, fruits and vegetables. During digestion, complex carbohydrates are broken down into simple glucose molecules in the small intestine. From there, glucose is absorbed into the bloodstream, causing blood glucose levels to rise.

The body responds by releasing insulin, a key anabolic hormone produced by the pancreas. Insulin plays a central role in maintaining energy balance and metabolic stability. Its primary function after feeding is to facilitate the uptake of glucose into cells, especially in muscle and liver tissue.

Inside the liver and muscles, some of this glucose is converted into glycogen, a storage form composed of long glucose chains. Glycogen is the body’s preferred short-term energy reserve. This conversion happens when there is a temporary surplus of glucose and the immediate energy demands are low. Glycogen is stored within cells and can be rapidly broken back down into glucose when needed, especially during physical activity.

When glucose is present in excess of both immediate energy needs and glycogen storage capacity, insulin promotes a different pathway known as lipogenesis. This is the metabolic process by which glucose is converted into fat for long-term energy storage. The fat created through lipogenesis is stored in adipose tissue, which can be located under the skin, between muscles or within the muscle fibres themselves.

Insulin facilitates fat storage in two key ways. First, it stimulates lipoprotein lipase, an enzyme that breaks down circulating triglycerides so that their components can be absorbed by tissues. Second, it promotes glucose uptake and its use for fat synthesis. Within muscle cells, glucose can serve as the backbone for synthesising fatty acids. In high-marbling breeds, insulin sensitivity in muscle tissue is higher, encouraging more intramuscular fat deposition. However, this process occurs in all cattle to some extent, depending on genetics, diet and metabolic condition.

In breeds predisposed to marbling, fat is laid down between and even within muscle fibres. These fat cells are embedded in the connective tissue structures that separate individual muscle fibres and fascicles, contributing to flavour, tenderness and juiciness.

Insulin also plays a vital role in promoting protein synthesis while inhibiting protein breakdown. It achieves this by activating anabolic pathways inside the cell and suppressing catabolic ones. As a result, insulin supports muscle growth and recovery, particularly in a fed and stress-free state.

Certainly. Here’s a clear follow-up paragraph that explains the terms anabolic and catabolic in context:

In this context, anabolic refers to the set of metabolic processes that build up complex molecules from simpler ones such as assembling amino acids into muscle proteins. These processes require energy and are essential for growth, repair, and maintenance of tissues. Catabolic processes, on the other hand, involve breaking down complex molecules like proteins, fats, or glycogen, into simpler ones to release energy. While both are natural and necessary, an optimal balance between them is crucial. Under stress, this balance shifts: catabolic processes dominate, leading to the breakdown of muscle protein and the mobilisation of fat stores, while anabolic activities like muscle building are suppressed. This shift helps the body survive in the short term but compromises long-term tissue quality, including meat structure in animals.

Within cells, glucose is either used immediately for energy or stored as glycogen. Insulin is responsible for facilitating both the short-term storage of glucose as glycogen and the long-term storage of excess glucose as fat. It functions most effectively under calm, fed conditions. Under stress, however, insulin is typically suppressed because the body prioritises immediate energy release over storage.

Even during stress, fat is still created, but in a way that makes it more accessible. Energy stored inside muscle fibres or within cells is more difficult to access quickly because it requires intracellular signalling and enzymatic activity. In contrast, fat stored between muscle fibres or under the skin is less protected and can be rapidly mobilised by hormone-sensitive enzymes when adrenaline is released.

Fat storage between muscle fibres does still occur in resting, fed animals, but stress shifts the pattern significantly. The fat created under stress is more oxidatively unstable, more prone to rancidity and less desirable in both meat quality and human nutrition. This type of fat serves as an emergency energy depot, not a long-term structural or flavour-enhancing component.

To clarify, glucose is the simple sugar absorbed from the intestine. Glycogen is the storage form within cells. When glycogen capacity is full, insulin facilitates the conversion of glucose into fat. After a meal, glucose enters the bloodstream and is used for energy, stored as glycogen, or converted into fat. During stress, adrenaline takes over, insulin is suppressed and the body switches from storage to mobilisation.

Fat stored within muscle fibres is a long-term reserve and structurally integrated, while fat stored subcutaneously or intermuscularly is more easily accessed during stress. The distinction is not only metabolic but functional. What supports flavour and meat quality in calm animals becomes a liability under chronic stress.

Why Insulin Is Suppressed Under Stress

During stress, hormones such as cortisol and adrenaline override insulin’s effects to prioritise energy mobilisation rather than storage.

Under chronic stress, cortisol induces insulin resistance in muscle tissue, prevents glucose uptake and fat deposition inside muscles, and redirects energy use to immediate survival.

A continued state of reduced insulin due to ongoing stress affects not only fat distribution but also impairs muscle growth and protein synthesis. Insulin plays a crucial anabolic role in promoting amino acid uptake and supporting the repair and construction of muscle tissue. When insulin is consistently low as in chronically stressed animals, protein synthesis is diminished, and protein breakdown may increase. This contributes to underdeveloped or poorly structured muscle fibres.

In the meat, this may be observed as a softer, less cohesive texture where the muscle appears to “fall apart” more easily, lacking the firmness and defined structure typical of well-developed muscle tissue. This structural weakness is also linked to reduced water-holding capacity and a tendency for the meat to appear pale, soft, and exudative (PSE-like), though PSE itself arises from different mechanisms such as rapid post-mortem pH decline.

Importantly, this phenomenon stands apart from both PSE and DFD (dark, firm, dry) conditions. Field observations in Nigeria have shown that even in clearly DFD carcasses, large regions of muscle tissue appear watery and poorly defined. This suggests that chronic stress and the resulting suppression of insulin can independently disrupt muscle development and integrity, regardless of whether the carcass fits classical PSE or DFD profiles. It points to an endocrine-linked (linked to the hormonal system) degradation of meat structure due to prolonged metabolic imbalance.

Marbling as a Long-Term Energy Reserve Explained

Intramuscular fat (marbling) serves as an internal energy buffer within muscle tissue. Unlike subcutaneous or intermuscular fat, which the body accesses quickly during stress or hunger, marbling fat is harder to mobilise. It exists as a form of locked energy for extended low-energy periods. This fat is surrounded by muscle fibres and connective tissue, making it less accessible to enzymes and hormonal signals. Functionally, it acts like money in a locked savings account, used only when external reserves are depleted. In meat production, a high degree of marbling indicates that the animal experienced consistent energy surplus without chronic stress, allowing the body to prioritise this long-term energy storage strategy.

But this raises a key biological question: why not store all fat, long-term and short-term, under the skin or between the muscles, where it is easier to access? Why did evolution favour a separate, less accessible reservoir of fat deep inside the muscle itself?

The answer lies in energy management and survival strategy. Subcutaneous and intermuscular fat are indeed more accessible and are prioritised during acute energy demands, such as fleeing predators or enduring short-term food scarcity. However, relying solely on these stores is risky in prolonged deprivation or during seasons of sustained food scarcity. If all fat were stored in these outer reserves, animals would burn through it too rapidly.

Intramuscular fat offers a metabolic safeguard. It is metabolically quieter, less reactive to stress hormones like adrenaline and less vulnerable to rapid depletion. By embedding energy inside the tissue most essential to survival (the muscles themselves), the body ensures a final line of defence: energy that can sustain movement and function when all other reserves are gone. This inner reservoir also avoids excessive bulking of the body, which could slow an animal down or make it more vulnerable to predation.

Thus, marbling evolved not as a primary energy depot but as an emergency reserve. Its presence signals an animal well-adapted to survive variable conditions, capable of building deep reserves only possible under steady nutritional intake and low stress.

2. Fat Redistribution Under Stress: Why It Happens and How

Understanding why fat shifts location in the body under stress begins with examining the hormonal landscape that governs these changes. When an animal experiences physical or psychological stress, its body initiates a rapid response to prioritise survival. This includes not just immediate energy mobilisation, but also the strategic relocation of energy reserves. In this section, we explore how stress hormones, particularly adrenaline and cortisol, reshape fat distribution by favouring storage in more accessible depots. This physiological shift helps the animal react quickly to danger but has lasting consequences for meat quality and nutritional composition.

The Role of Adrenaline in Accessing Fat Reserves

Adrenaline (epinephrine) is a hormone produced by the adrenal glands in response to stress. It plays a key role in the body’s immediate survival mechanisms, often referred to as the ‘fight-or-flight’ response.

Adrenaline mobilises energy reserves through several pathways:

• Fat Breakdown (Lipolysis): Adrenaline activates hormone-sensitive lipase (HSL), breaking down fat stores into free fatty acids (FFA) and glycerol. These components are released into the bloodstream and used as energy sources, especially when glucose availability is limited.
• Subcutaneous and Intermuscular Fat: These fat depots consist of larger, loosely structured fat cells located in open spaces between muscle groups or beneath the skin. Their accessibility via blood vessels and fewer connective tissue barriers makes them responsive to adrenaline and metabolically active.
• Intramuscular Fat (Marbling): Fat stored within muscle fibres is embedded deep inside muscle structure, surrounded by connective tissue. This structure limits hormone access, making intramuscular fat less responsive to adrenaline. Mobilising this fat would require muscle tissue degradation, which is avoided under normal stress conditions.

Adrenaline, Anaerobic Metabolism, and Lactic Acid

In addition to mobilising fat, adrenaline influences carbohydrate metabolism:

• Shift to Anaerobic Metabolism

Muscle cells rely heavily on oxygen to efficiently produce energy through a process known as aerobic respiration. In this pathway, oxygen acts as the final electron acceptor in the mitochondrial electron transport chain, allowing for the complete oxidation of glucose into carbon dioxide and water. This not only generates a high yield of ATP (the energy currency of the cell) but also helps maintain electron balance within the cell’s energy systems.

However, during periods of extreme stress or intense muscle activity, such as during escape responses or chronic environmental strain, the oxygen supply to muscles may become insufficient. This can happen because blood flow is redirected to critical organs or because the rate of oxygen delivery cannot keep up with the demand. When this occurs, the muscle switches to anaerobic glycolysis, a backup energy pathway that does not require oxygen.

While anaerobic glycolysis allows for rapid ATP production, it is far less efficient and results in the accumulation of lactic acid, a by-product of incomplete glucose breakdown. This shift not only contributes to muscular fatigue but also signals a stressed physiological state. Over time, reliance on anaerobic metabolism due to frequent stress can affect muscle biochemistry, meat quality, and energy storage patterns in the animal.

• Lactic Acid Production

When oxygen is limited, cells cannot complete aerobic respiration because there is no final electron acceptor in the mitochondrial electron transport chain. This disrupts the normal oxidative breakdown of glucose and leads to a metabolic bottleneck: without oxygen, NADH (a carrier of high-energy electrons produced during glycolysis) cannot pass its electrons into the mitochondria to regenerate NAD⁺.

To resolve this redox imbalance and prevent the complete shutdown of energy production, cells activate an alternative pathway. The molecule pyruvate, which is the end product of glycolysis, now plays a vital compensatory role. It accepts electrons from NADH and is reduced to lactate (commonly called lactic acid). This conversion effectively regenerates NAD⁺, enabling glycolysis to continue operating under anaerobic conditions.

Although this anaerobic process yields only a small amount of ATP compared to aerobic respiration, it is fast and critical for short-term survival, especially in muscle tissue. However, the accumulation of lactic acid leads to a drop in local pH, contributing to the sensation of muscle fatigue and metabolic acidosis. In meat science, elevated levels of lactate in muscle post-mortem can contribute to lower pH, influencing water-holding capacity, tenderness, and shelf life, key factors in assessing meat quality.

• Byproduct Role of Lactic Acid

To understand the importance of lactic acid, it’s crucial to first grasp what glycolysis is. Glycolysis is the initial metabolic pathway for breaking down glucose, a simple sugar derived from dietary carbohydrates, into pyruvate. This sequence of reactions occurs in the cytoplasm of the cell and yields a modest amount of ATP (adenosine triphosphate), the essential molecule for cellular energy. Glycolysis operates both in the presence (aerobic) and absence (anaerobic) of oxygen, making it a flexible and vital system for energy production.

Under non-stressful, well-fed conditions, the body doesn’t immediately convert glucose into fat. Instead, it first stores energy in the form of glycogen, a branched polymer of glucose that is kept primarily in liver and muscle cells. Glycogen serves as a rapid-access energy reserve, easily mobilised when glucose levels in the blood fall. Only when glycogen stores are full and energy intake remains high does the body begin converting excess glucose into fat through lipogenesis.

However, in oxygen-deprived situations, such as high-intensity exertion or acute stress, the body cannot rely on aerobic metabolism. In such cases, glycolysis becomes the dominant energy pathway. As described earlier, pyruvate is then converted into lactic acid to regenerate NAD⁺, allowing glycolysis to continue even in the absence of oxygen.

Far from being a mere waste product, lactic acid serves an essential regulatory function. It enables continued ATP generation during moments of intense physical demand when other pathways falter. This makes it a critical fuel buffer during fight-or-flight responses, supplying energy to muscles when survival is at stake.

In fact, lactate can later be converted back into glucose in the liver through the Cori cycle, demonstrating its temporary role as a metabolic currency rather than a dead-end product. From a meat science perspective, elevated lactate levels at slaughter can influence pH decline post-mortem, affecting everything from meat tenderness and water retention to colour stability and shelf life. This further highlights the connection between metabolic stress and final meat quality.

3. Impact on Oxidation Stability, Sensory Quality, and Shelf Life

The type and distribution of fat in meat not only influence nutritional properties but also play a critical role in how the product ages, tastes, and retains quality. This section explores how intramuscular (marbling) versus intermuscular fat responds differently to oxidative stress, how these differences impact eating quality, and why stress-induced shifts in fat distribution compromise both the shelf life and sensory appeal of beef. Understanding these relationships is essential for processors, retailers, and consumers who value meat that is not only healthy but also flavourful and stable over time.

Impact on Oxidation Stability, Sensory Quality, and Shelf Life

The location and biochemical nature of fat in beef significantly influence its oxidative stability, flavour development, and storage potential. Fat is not chemically uniform across the body. Depending on where it is stored, within the muscle fibres (intramuscular or marbling), between muscles (intermuscular), or beneath the skin (subcutaneous), its composition and reactivity change, with important consequences for the quality and stability of meat products. This section explores these differences and their implications.

Oxidation Stability

Marbled fat, embedded inside muscle fibres, is chemically distinct from fat located between muscles or under the skin. One key difference lies in fatty acid composition. Intramuscular fat typically contains a higher proportion of monounsaturated fatty acids (MUFA), particularly oleic acid. These fats are more resistant to oxidative degradation compared to polyunsaturated fatty acids (PUFA), which dominate in intermuscular and subcutaneous fat depots.

PUFAs, with multiple double bonds, are highly susceptible to lipid peroxidation. When exposed to oxygen, light, or elevated temperatures, they break down rapidly, forming reactive aldehydes and other compounds responsible for rancidity. This is particularly relevant for intermuscular fat, which is exposed to more oxygen during processing, cutting, and storage. In contrast, marbled fat is physically shielded by surrounding muscle tissue, limiting oxygen exposure and slowing down the oxidation process.

Sensory Impact

The biochemical and structural differences between these fat types translate directly into eating quality. Marbled fat melts during cooking, infusing the meat with flavour compounds and improving mouthfeel. It enhances juiciness by lubricating the muscle fibres and contributes to a richer, more satisfying flavour profile (Savell and Cross, 1988). These sensory benefits are supported by the higher MUFA content, particularly oleic acid, which is known for its mild and pleasant taste.

Intermuscular fat, on the other hand, has a more neutral role in flavour enhancement and can even introduce negative sensory effects. Because of its higher PUFA content and greater exposure to oxidation, it is prone to developing off-flavours, such as the warmed-over flavour (WOF) commonly encountered in reheated meat. WOF is linked to lipid peroxidation products like hexanal and 2,4-decadienal, which form readily in PUFA-rich fat exposed to air.

Shelf Life and the Influence of Stress

The fat distribution patterns induced by chronic stress have further implications for shelf life. Meat from stressed animals often has lower levels of protective intramuscular fat and higher concentrations of intermuscular and subcutaneous fat, which are more susceptible to oxidation. As a result, such meat oxidises faster and is less resilient to temperature fluctuations and storage time.

Additionally, chronic stress can reduce the water-holding capacity of muscle tissue by impairing protein structure and depleting glycogen reserves. This results in drier, softer meat with a shorter shelf life. Structural integrity is compromised, making the meat more prone to drip loss, discolouration, and microbial spoilage.

Why Location Matters

The location of the fat plays a fundamental role in its chemical stability and interaction with surrounding tissue. We have stated this a number of times now. Fat under the skin is loosely held and structurally isolated from muscle activity. Fat between the muscles is more integrated into fascial planes and connective tissues, but remains relatively exposed. In contrast, marbled fat is intimately woven into the muscle fibre network. This deeper integration shields it from environmental oxygen and light while enabling slower, more controlled melting during cooking.

Furthermore, enzymatic activity around muscle tissue also influences lipid metabolism. The intramuscular environment is more regulated and less prone to spontaneous breakdown, whereas intermuscular and subcutaneous fat are more exposed to enzymatic and oxidative activity post mortem.

4. Health Considerations

Understanding how fat is distributed and metabolised in both animals and humans provides valuable insight into health, meat quality, and nutritional value. Fat is not a uniform substance—it varies chemically and biologically depending on its location, function, and the metabolic context in which it is deposited. This section explores the importance of lean muscle mass, the biochemical differences between fat types, and how the hormonal environment—especially under stress—redirects energy use and storage. These elements profoundly affect both animal welfare and the nutritional and sensory qualities of meat.

Lean Muscle Mass and Fat Distribution

Lean muscle mass refers to the proportion of the body composed of muscle tissue, excluding fat. In both animals and humans, a high lean muscle mass is indicative of good metabolic health, efficient physical performance, and—in meat production—high carcass yield. Importantly, lean mass is associated with low levels of subcutaneous and intermuscular fat, but not necessarily with an absence of intramuscular fat, or marbling.

In livestock, the ideal is to maintain a high proportion of lean tissue while allowing for moderate marbling. This balance improves meat yield and palatability while avoiding excessive external fat that reduces carcass value and complicates processing. In humans, maintaining lean mass is critical for glucose control, reduced risk of metabolic syndrome, and sustained strength and mobility.

Is Marbling Unhealthy for the Animal?

Intramuscular fat—or marbling—is not a sign of pathology. Rather, it reflects a physiological response to an energy surplus under low-stress conditions. In breeds selectively developed for premium meat, marbling represents a non-invasive, hormonally regulated fat depot that does not impair the animal’s health or function. It accumulates gradually and locally within muscle fibres, suggesting a finely controlled, metabolic mechanism.

Conversely, the excessive accumulation of fat in intermuscular and subcutaneous areas can burden the animal’s system. These depots store larger quantities of fat in bigger adipocytes and are more metabolically demanding, particularly when deposited in response to chronic stress. These fat stores are less desirable from both a health and efficiency perspective, increasing feed costs and reducing the animal’s mobility and productivity.

The Difference Between Saturated and Unsaturated Fats

The key structural difference between saturated and unsaturated fats lies in the bonding between carbon atoms in their fatty acid chains. Saturated fats contain no double bonds; their carbon chains are straight and compact, allowing the molecules to pack tightly together. This tight packing results in fats that are solid at room temperature. Unsaturated fats contain one or more double bonds, introducing bends in the chain that prevent tight packing, making them liquid at room temperature.

Subcutaneous and intermuscular fats, especially those deposited under stress, are richer in saturated fatty acids (SFA). These fats are chemically stable and dense, intended for long-term energy storage. In contrast, marbling fat within muscle fibres contains a higher proportion of monounsaturated and polyunsaturated fatty acids (MUFA and PUFA). These unsaturated fats are more fluid, biologically active, and responsive to metabolic signals.

Why This Difference Matters for the Animal

In a calm and well-fed animal, fat deposition is gradual and strategically regulated. Unsaturated fats within marbling are integrated into the muscle environment, providing localised energy support and contributing to structural integrity. These fats are easier to mobilise in small amounts and support sustained metabolic function.

Under stress, however, the body prioritises survival mechanisms. Hormones such as adrenaline and cortisol suppress insulin and shift energy usage away from storage. This results in the preferential accumulation of saturated fat in outer depots, which serve as immediate energy reservoirs. These shifts compromise the deposition of intramuscular fat and increase reliance on intermuscular and subcutaneous stores, which do not support fine motor activity or energy balance as efficiently.

Why This Matters for Human Health

From a dietary perspective, the distinction between fat types has measurable health consequences. Saturated fat consumption is linked to elevated levels of LDL cholesterol, which contributes to arterial plaque formation and increases the risk of cardiovascular disease. While not all saturated fat is equally harmful, habitual overconsumption in the context of a low-fibre, high-calorie diet can significantly impact heart health.

In contrast, unsaturated fats—especially those found in marbled meat—tend to improve lipid profiles by lowering LDL and, in some cases, raising HDL cholesterol. These fats also contribute to a more pleasant mouthfeel, enhanced flavour, and improved oxidative stability of the meat. Thus, premium meat products aim to maximise intramuscular fat while minimising saturated-rich external fat, creating a product that is both sensorially superior and nutritionally balanced.

5. Practical Implications for Beef Producers

A comprehensive understanding of how fat is deposited, mobilised, and transformed under various physiological conditions equips beef producers with the tools to make evidence-based decisions. The interplay between genetics, nutrition, welfare, and stress management is critical in producing meat that meets modern quality, health, and economic standards.

Breed Selection

Genetic predisposition plays a crucial role in determining the distribution and composition of fat. Selecting breeds with a natural tendency to develop intramuscular fat (e.g. Wagyu, Angus) allows for the production of beef with desirable marbling. This trait should be prioritised in breeding programmes aimed at optimising both eating quality and metabolic health outcomes.

Stress Management

Stress alters hormonal cycles, suppresses insulin activity, and redirects energy away from marbling towards fat depots more suited for emergency energy access. Implementing practices that minimise stress—such as low-stress handling, stable social groupings, and controlled environments—preserves the metabolic pathway required for intramuscular fat synthesis and supports animal welfare.

Feeding and Processing Adjustments

Feeding strategies should aim to provide a steady and surplus energy intake, enabling marbling development without overaccumulating external fat. This includes staged finishing diets, adequate forage-to-grain transitions, and insulin-stimulating nutritional profiles. Post-harvest processing must consider the oxidative stability of different fat types: marbled meat is more stable, while intermuscular fat requires tighter cold chain management to prevent flavour deterioration.

Conclusion

Marbling represents more than visual appeal or luxury; it is the biochemical signature of an unstressed animal in energetic abundance. It arises only when hormonal conditions favour insulin-mediated glucose uptake and deposition of unsaturated fats directly into muscle tissue. By contrast, intermuscular and subcutaneous fat are stress-responsive energy depots—evolutionary tools for survival, but often detrimental to meat quality.

The science is clear: stress is not just a welfare concern but a metabolic shift. It alters fat type, location, oxidation rate, and even flavour. Producers who invest in genetics that favour marbling, implement feeding regimes that support steady energy balance, and ensure low-stress environments will not only meet consumer expectations but also improve meat yield, quality, shelf life, and health value.

By recognising marbling as a physiological outcome of calm, thriving animals, beef producers can reframe their entire production ethos, shifting from managing survival to cultivating excellence.

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Author’s Note

This article forms part of the EarthwormExpress research series, providing applied insights for meat scientists and industry professionals.