Bone Collagen: From Ancient Broths to Modern Food Science

By Eben & Kristi van Tonder, 19 September 2025

A response to Mark’s question

Introduction

Kristi’s chicken soup is a great example of the value of collagen and how easily accessible it is. What looks like a simple family recipe is in fact part of a very long tradition of unlocking nutrition from bones. Her broth, simmered all day until the meat fibres fall away and the liquid sets into a golden gel, embodies the same biochemical transformation that sustained ancient miners, travellers, and convalescents across cultures.

When Mark asked about the traditions and technologies of making bones edible, the question touched directly on a subject I have pursued for years: collagen and, in particular, bone collagen. Too often discarded as waste, bones are in fact one of humanity’s oldest and most reliable nutritional resources. Across continents, they have been transformed into broths, soups, and extracts that served both the poor and the powerful, the sick and the strong.

Kristi, my wife and collaborator, describes this heritage in her own words:

“When considering bones in the context of food preparation, bone broth immediately comes to mind. It is one of the oldest examples of how bones have been used as nourishment. Across nearly all cultures, in Europe, Asia, and Africa alike, bones have been simmered since antiquity. Often regarded as ‘poor people’s food,’ broth provided a nutritious meal even from the simplest of scraps.”

Her reflection reminds us that broth belongs as much to cultural history as to biochemistry. What may look like a pot of leftovers is, in fact, a technology of survival and resilience, carrying knowledge from antiquity into our own kitchens.

This article is a response to Mark’s question. It follows the thread of bone collagen from ancient practices in Hallstatt’s Bronze Age curing vats, through Kristi’s family recipe, to its modern application as a functional food for athletes seeking endurance and recovery. In doing so, it shows that what begins as scraps and bones becomes a science of nutrition that has never lost its relevance.

The Nutritional and Cultural Role of Bone Broth

Bone broth has been central to human nutrition for millennia. By boiling bones over long periods, people discovered a way to extract hidden value in the form of proteins, minerals, and amino acids that would otherwise remain locked in tissue that could not be eaten directly. These broths were not luxuries but lifelines, especially for the sick, the poor, or communities with limited access to meat.

Through slow cooking, bones release collagen, gelatin, calcium, magnesium, phosphorus, and amino acids such as glycine, proline, hydroxyproline, and cysteine. These nutrients have long been associated with the resilience of joints, the maintenance of skin health, the support of digestion, and the process of recovery. What we describe today in biochemical terms, the unwinding of collagen helices, the gelation of proteins, the fragmentation into peptides, was already recognised in practice by cooks of the distant past. They may not have spoken of “hydroxyproline” or “amino acids,” but they knew that a pot left long at the fire yielded a jelly that set firm when cooled, or a clear restorative broth that revived the weak.

To appreciate the role of broth, it is important to distinguish between collagen, gelatin, and peptides. Collagen is the intact fibrous protein that forms the structure of skin, tendons, and bone. When it is heated in water, the triple helix structure unwinds and becomes gelatin, which dissolves into the liquid and sets again when cooled, giving broth its characteristic jelly-like consistency. With further cooking or the presence of mild acidity, gelatin continues to break down into collagen peptides, which are shorter protein fragments. These peptides are absorbed more rapidly in the human body and directly stimulate new collagen production. Each stage, whether collagen, gelatin, or peptides, contributes in a distinct way to the unique nutritional value of broth.

This transformation, which we can now test with agitation and observe in foaming or gel strength, was once diagnosed only with eye, hand, and taste. Yet across antiquity, from Roman kitchens that prized meat jellies, to Chinese medical decoctions, to African postpartum broths, people implicitly recognised that different treatments of bones and skins yielded broths of different power. The modern understanding of collagen chemistry does not replace this older wisdom but confirms its depth. Looking forward, this same logic will reappear in the following sections, as we examine how ancient miners, herders, and travellers everywhere harnessed broth not just as food, but as a portable and resilient technology of survival.

Identifying Collagen, Gelatin, and Peptides in Broth

Understanding how collagen transforms into gelatin and then into peptides is central to broth-making. Each stage not only changes the chemistry of the liquid but also alters its behaviour in ways that can be observed without laboratory tools. Traditional cooks relied on these sensory signs, and with a bit of knowledge, they can be systematically interpreted.

When collagen is still intact, the broth remains thin even after cooling. Tissues such as skin or connective fibres stay tough and stringy, and the liquid has little viscosity. At this point, stirring or agitating the broth produces almost no foam, because intact collagen fibres are insoluble and do not migrate to the surface. This early stage is most common after only one or two hours of simmering.

As heating continues, collagen unwinds and dissolves into gelatin. The key sign of this stage is that the broth sets into a firm gel when cooled. Gelatin still consists of relatively large protein chains, which explains why it has such strong water-binding and gel-forming capacity. If the broth is stirred vigorously, it produces a light foam, since gelatin molecules are surface-active and momentarily stabilise bubbles. This foam, however, dissipates quickly, reflecting the balance between protein size and solubility.

With further cooking, or if mild acidity is present, gelatin continues to break down into shorter fragments known as collagen peptides. These peptides are far more soluble and no longer form gels, so a broth dominated by peptides will remain liquid or only set weakly when cooled. Here, the stirring test becomes particularly revealing: peptide-rich broths foam readily when agitated, and the foam tends to persist. This is because short peptides are highly surface-active and, when combined with lipids, can stabilise bubbles far more effectively than intact gelatin.

Foaming itself is not harmful, but it may be undesirable in culinary contexts where clarity and texture are valued. The problem can be controlled by gentle simmering rather than boiling, as violent bubbling incorporates excess air. Early removal of denatured proteins (the scum that forms on the surface) reduces foaming later, and skimming off excess fat prevents lipids from binding to peptides at the air–liquid interface. Stirring gently rather than whisking helps avoid unnecessary air incorporation.

For those seeking to concentrate on specific fractions, the stages can be further managed. Collagen, being insoluble, is best “concentrated” not by cooking but by preparing the tissue itself, cutting it into smaller pieces before extraction. Gelatin is concentrated by reducing the liquid volume through slow evaporation, yielding a strong gel on cooling. Peptides, once present, can be concentrated by low-heat evaporation or, in industrial settings, vacuum concentration or spray drying, since they remain soluble and do not gel.

The agitation test thus offers a simple, practical way to diagnose what stage a broth has reached. Little to no foam indicates intact collagen; a broth that gels on cooling and foams lightly when stirred is dominated by gelatin; and a liquid broth that produces persistent foam when agitated signals that peptides are abundant. By combining this observation with careful control of cooking time, temperature, and acidity, one can guide the broth toward the desired nutritional and textural outcome.

The Chemistry of Collagen Extraction

To extract the full value of bones, one must understand the chemistry of collagen breakdown. Collagen fibrils begin to unwind at around 57–62°C. By 70–80°C, they convert into gelatin, dissolving into the broth (Shoulders & Raines, 2009). With prolonged cooking or mild acidity, gelatin fragments further into collagen peptides, which are easily absorbed in the intestine and directly stimulate new collagen production in the body (Ran & Wang, 2014).

The mineral component of bone, hydroxyapatite, is less soluble. Acidity is key here: vinegar, lemon juice, or wine lowers pH and enhances the release of calcium, magnesium, and phosphorus (Nakamura et al., 2017). This is why many traditional recipes, across continents, call for an acidic addition to broths.

How Long and at What Temperature?

Cooking time and temperature shape the quality of broth. Shorter cooking produces lighter, more delicate broths; longer simmering yields maximum extraction.

  • 6–8 hours at 80–90°C produces good collagen-to-gelatin conversion. This results in a broth that sets when cooled but remains light in flavour. Mrs. Beeton (1861) recommended this duration for beef tea in her Book of Household Management.
  • 12–24 hours at gentle simmer ensures maximum extraction of gelatin and amino acids. The resulting broth gels firmly and carries a deep flavour. Escoffier (1903) prescribed similar durations for his fonds brun, while Jewish Sabbath soups were famously left simmering overnight.
  • Acidified broths extract more minerals. Adding vinegar or lemon juice enhances calcium and magnesium yield. Li Shizhen in 16th-century China recommended vinegar to “draw out the strength of bones.” In parts of West Africa, palm wine was used for similar purposes in postpartum soups.
  • Rapid boiling, though tempting, degrades delicate compounds and risks muddy flavours. Medieval cookbooks like Le Viandier de Taillevent (14th c.) cautioned against violent boiling, preferring slow, steady heat.

Each method reflects both chemistry and culture, converging on the same insight: patience unlocks nutrition.

Ancient and Ethnographic Differentiation of Collagen, Gelatin, and Peptides

Although the vocabulary of collagen, gelatin, and peptides is modern, ancient cooks were acute observers of texture, digestibility, and medicinal effect. Across cultures, we find evidence that they manipulated time, temperature, and acidity to produce broths with distinct characteristics, some jelly-like, others light and clear, others medicinally potent.

1. Roman Bone Broths and Medicinal Jellies (Gelatin stage)
Apicius, the famous Roman cookbook (4th–5th century CE), contains recipes for ius album (white broth) and meat jellies prepared from boiled feet and ears of animals (Apicius, Book VII, On Jellies). These recipes intentionally used collagen-rich tissues to produce a broth that would set into a firm gel when cooled. Romans recognised the difference between a broth that remained liquid and one that became “glued together,” and the jellied form was prized for banquets and for preservation (Dalby, 2003). This corresponds closely to the gelatin stage, where large proteins form a strong gel, providing both texture and concentrated nutrition.

2. Traditional Chinese Medicine: “Long vs. Short Decoctions” (Collagen vs. Peptide stage)
In Traditional Chinese Medicine (TCM), bones and connective tissues are simmered for different durations depending on the desired effect. A “short decoction” (2–3 hours) produces a light broth used for daily nourishment, collagen is partly intact, and gelatin dominates. By contrast, a “long decoction” (12–24 hours) is prescribed for convalescence or post-partum recovery, producing a clear but deeply nutrient-rich broth that does not gel as strongly. The difference reflects the conversion of gelatin into smaller peptides, which were implicitly recognised as more “penetrating” and restorative (Simoons, 1991).

3. Medieval European Court vs. Peasant Broths (Collagen vs. Peptides)
Ethnographic accounts from medieval Europe distinguish between two main types of broths. Courtly kitchens produced highly clarified consommés, simmered briefly, which cooled without strong gelling, prized for elegance and digestibility (Scully, 1995). Peasant households, however, simmered bones and skins overnight, producing heavy, jelly-like stocks that set firmly when cooled. The former corresponds more closely to peptide-rich broths (light, restorative, non-gelling), while the latter reflected the gelatin stage, thick and energy-dense. The difference was not accidental: clarification involved skimming, straining, and shorter cooking, which limited gelatin breakdown.

4. Ethnographic Evidence from West Africa (Peptide-rich broths)
In Nigeria and Ghana, ethnographers (Goody, 1982) recorded that bones were often simmered for long durations, not for their meat value but for their medicinal broth, especially for the sick or women after childbirth. Such broths were light and clear but nutrient-rich, matching what we would today identify as peptide-dominant extractions. These were valued not for texture but for perceived restorative power, a recognition of differences in digestibility and bioavailability.

The Science of Collagen Transformation in Skin and Bone

Collagen-rich tissues behave differently depending on whether they come from skin or bone. Both can be transformed into gelatin and collagen peptides through careful cooking, but the optimal conditions vary because of differences in structure and composition. Understanding these differences is essential for broth-making, for industrial processing, and for evaluating nutritional outcomes.

Collagen Transformation in Skin

Skin is largely made up of collagen fibres embedded in a relatively soft connective tissue matrix. This structure allows collagen to be extracted with relative ease during cooking. Denaturation begins at around 57 to 62 °C, when the collagen triple helix starts to unwind. At 70 to 80 °C, gelatin is formed in significant quantities, provided the broth is held at this temperature for several hours. With extended simmering of 12 to 24 hours, especially in the presence of mild acidity, gelatin further breaks down into shorter collagen peptides that are highly bioavailable and stimulate new collagen production in the body.

Acidity plays a central role by lowering the pH into the range of 5.5 to 6.5, which accelerates hydrolysis and improves the solubilisation of amino acids. Gelification is reversible at this stage: gelatin dissolved in hot water will set into a gel when cooled, but once it fragments into peptides, the reversible gel property is lost.

Particle size also affects efficiency. Coarse cutting at 4.5 mm releases collagen slowly, while finer cutting at 3 mm or 2 mm increases surface area and accelerates extraction. Over-grinding to 1 mm or micron size, such as in high-pressure homogenisers or mechanically deboned meat, risks heat and shear damage that weakens gel strength. For practical purposes, cutting to 2–3 mm in a mincer or bowl cutter strikes the best balance between surface area and protein integrity.

When collagen-rich tissues are reduced to very fine particles, two forms of damage can occur: heat damage from frictional energy and mechanical damage from excessive shear forces. Both reduce the ability of gelatin to later form a strong gel.

Heat damage is easiest to understand. As blades rotate at high speed, friction generates local heat in the protein mass. If the material temperature rises above 40 °C, collagen fibres begin to lose their native structure. By 50 °C, partial denaturation is already taking place, and by 60 °C or higher, collagen may convert prematurely to soluble gelatin inside the cutter. Once this happens, the protein fragments are too short to re-form into an ordered gel during cooling, and much of the functional strength is lost.

Mechanical damage occurs even when the temperature is kept low. Collagen is organised in long fibrils that give structural integrity. If these fibrils are shredded into fragments that are too small or irregular, they can no longer align during gelation. This produces a brittle, weak, or non-setting gel. The risk is highest when particle size falls below 1 mm, as in emulsifiers or mechanically deboned meat systems. Excessive shear can also trap air into the mass, leading to foaming and oxidative damage, both of which reduce the clarity and stability of the final broth.

How to recognise mechanical or heat damage
The signs are visible in both the processing and finished broth. In processing, a sudden rise in cutter temperature despite added ice indicates excessive shear. A paste that feels overly sticky, foamy, or greasy during cutting is another warning sign. In the finished broth, a properly ground 2–3 mm particle size will produce a firm, translucent gel when cooled. Over-ground or damaged material produces a cloudy broth and a gel that is weak, crumbly, or fails to set at all.

Prevention strategies
The key is to balance surface area with structural integrity. Grinding to 2–3 mm in a mincer or bowl cutter provides sufficient exposure for efficient extraction while keeping the fibres largely intact. Sharp blades are critical: blunt blades tear and smear collagen fibres instead of cutting cleanly, increasing shear and heat. Processing should be done in small batches with chilled material, maintaining the temperature below 12 °C at all times and ideally under 8 °C. If the mass rises above 18 °C, risk of damage becomes significant, and at 25 °C or higher, gel strength is often permanently lost. Adding ice or chilled water during cutting helps stabilise temperature and reduces friction. Avoiding prolonged residence times in the cutter is equally important, as continuous recirculation compounds both shear and heat exposure.

In summary, over-grinding is identified not just by particle size but by its combined effect on temperature, fibre integrity, and gel strength. Keeping grind size at 2–3 mm, maintaining sharp blades, working with chilled raw material, and preventing the product from exceeding 18 °C during cutting ensures collagen functionality is preserved for optimal broth extraction.

Collagen Transformation in Bone

Bones are more complex because their collagen is bound within a rigid mineral framework of hydroxyapatite. This slows extraction and requires different strategies. Collagen conversion to gelatin still occurs in the 70 to 80 °C range, but the mineral phase means longer times are needed. Prolonged simmering of 12 to 24 hours at 80 to 90 °C is typically necessary, and the use of mild acidity is essential. Adding vinegar, lemon juice, or wine lowers the pH toward 5.5–6.0, which accelerates the solubilisation of calcium, magnesium, and phosphorus along with collagen. If the pH drops too far, however, excessive demineralisation produces a chalky taste and destabilises flavour.

Mechanical preparation is also more critical for bones than for skin. Large bones yield little unless they are sawn into smaller blocks that expose internal surfaces. For chicken bones, grinding in a bowl cutter to 2–3 mm gives the best results, maximising surface area without creating the heat and shear damage seen in ultra-fine emulsification. Cooking whole bones without cutting is traditional and produces a lighter, clearer broth, but yields less collagen and fewer minerals. Ground or cut bones provide denser nutrition, though the resulting broth is often cloudier.

In both skin and bone, the art lies in balancing time, temperature, pH, and particle size. Skin releases collagen more readily and requires less intervention, while bones demand longer cooking, mechanical reduction, and acidity to liberate their nutrition. Together, they represent complementary strategies in broth-making, one focused on rapid collagen availability and the other on deep mineral and protein extraction.

Emerging Technologies: High-Pressure Collagen Processing

High-pressure homogenisation or microfluidisation forces collagen-rich material through a very small aperture at extreme pressure, often 200 to 1500 bar, and then releases it suddenly into atmospheric pressure. The rapid drop creates intense shear, cavitation, and turbulence, breaking particles into micron or even submicron sizes.

For collagen, this process fragments fibrils and exposes far more surface area. The result is rapid solubilisation and accelerated conversion into peptides that are more easily absorbed in the human intestine. In supplement or beverage applications, this can be an advantage, since smaller peptides cross the intestinal barrier more efficiently and remain stable in solution.

The risks are equally clear. Excessive shear can denature proteins irreversibly, destroying the ability of collagen to form a gel. Instead of structured gelatin, the outcome may be a clear solution of fragments with no gelling strength. While this is desirable in nutraceutical powders or sports drinks, it undermines the culinary and textural qualities valued in broths, aspics, and sausages. High-energy processing can also induce oxidation, particularly of sulphur-containing amino acids such as cysteine, leading to reduced nutritional and flavour stability.

Meat proteins in general contain a modest but important fraction of sulphur-containing amino acids, especially cysteine and methionine. Together, they represent about 3 to 4 percent of total amino acids in skeletal muscle, and although collagen contains less cysteine than proteins like keratin, it still relies on sulphur groups for cross-linking and stability. Under the extreme conditions of high-pressure homogenisation, these sulphur bonds are prone to oxidation. This not only reduces nutritional quality but can also generate sulphurous flavours and compromise the stability of the extract.

By contrast, applying such technology to plant proteins may offer clearer advantages. Many plant-derived proteins are locked within fibrous cell walls, bound to anti-nutritional factors, or resistant to enzymatic digestion. High-pressure micronisation can disrupt these structures, improve solubility, and enhance digestibility. Since most plant proteins contain fewer sulphur-containing amino acids than meat proteins, the risk of oxidative degradation is lower. The method could therefore be better suited for upgrading under-utilised plant biomass into functional protein ingredients, while for meat and collagen, it risks degrading the very gel-forming qualities that make these proteins valuable in culinary and traditional food applications.

In summary, micronisation by high-pressure homogenisation offers benefits when the aim is maximum solubility and peptide bioavailability, but it carries trade-offs in gel functionality and sensory quality. For collagen-rich animal material, traditional low-temperature simmering remains superior for preserving gel strength and flavour, whereas for plant proteins, the technology may be highly beneficial by overcoming structural barriers and enhancing nutritional accessibility.

Case studies from Hallstatt, Noricum, and the Celtic world

The logic of broth extends beyond tradition: it is a strategy for turning waste into nourishment. Kristi reflects:

“Whenever I see bone by-products from industrial deboning, I cannot help but think how valuable it would be to turn them into broth – sawing, simmering, seasoning, reducing. The idea of transforming supposed ‘waste’ into something nourishing and beneficial continues to fascinate me.”

This echoes Bronze Age Hallstatt, where archaeologists discovered curing vats filled with pig bones and meat juices. These were reduced into proto-bouillon tablets, Europe’s first industrial soup seasoning (Grömer, 2016). Waste became wealth, just as today’s meat industry could turn by-products into health-promoting broths.

The Bronze and Iron Age north-Alpine salt zone (Hallstatt–Dürrnberg) and wider Celtic Europe left a surprisingly rich archaeological record for how people cooked, cured, and extracted value from animal tissue. While explicit “recipes” for bone broth are rare, the combination of installations, vessels, residues, and faunal assemblages shows that people understood the same levers we use today of gentle heat, time, acidity, and cut size to pull collagen and flavour from bone and connective tissue.

Large cauldrons played an important and prestigious role in the Celtic cultures of Europe; examples include the famous Gundestrup Cauldron and the krater found in the burial of the Lady of Vix. The Vix Krater, discovered in 1953 in the burial of a Celtic princess near Châtillon-sur-Seine in Burgundy, dates to around 500 BC. Made in the Greek world, probably in Magna Graecia, it is the largest known ancient bronze vessel, standing 1.64 meters high, weighing over 200 kilograms, and with a capacity of about 1,100 liters. Its decoration includes a frieze of hoplites and chariots and handles adorned with Gorgon heads. As a prestigious grave good, the krater testifies to long-distance trade and cultural contacts between the Celtic elites of central Europe and the Mediterranean world.

Hallstatt (Upper Austria): industrial curing with by-products compatible with broth making

Sandmann, Franz Xaver. Salzbergwerk in Hallstatt [Salt mine in Hallstatt]. Hand-coloured lithograph, ca. 1825–1835. Österreichische Nationalbibliothek, Vienna.

Work in the Salzbergtal above Hallstatt documents a true meat-processing industry in the Late Bronze Age: log-built clay-sealed curing vats (Blockbauwannen) large enough for sides of pork; selective use of pig portions (long bones, lower jaws); and curing cycles on the order of ten days before further maturation in the cool, ventilated mine air (Grömer, 2016; Reschreiter & Kowarik, 2019). One of these vats was large enough for 200 sides of pork. These finds demonstrate salt-driven protein processing on a scale far beyond local subsistence. Scholars emphasise brine creation and re-use, split bones, and post-cure maturation, exactly the sort of workflow that produces protein-rich drippings and brines that are readily boiled down into stocks or concentrates, even if “broth” itself is not named in the record.

Kristi van Tonder, in an email communication to Mark Hay (2025), drew on scholarly interpretations to link the archaeological findings with the wider human tradition of broth-making.

She explained that researchers often connect animal bones in the archaeological record with one of the oldest and most widespread practices of nourishment: simmering them into broth. In cultures across Europe, Asia, and Africa, the slow cooking of bones has for millennia produced inexpensive but nutritious meals. What began as a way for poorer households to extract value from scraps became a long-standing tradition. Through extended simmering, bones release collagen, gelatin, and minerals such as calcium, magnesium, and phosphorus, along with amino acids — substances believed to support joint function, bone strength, digestion, and recovery. In Traditional Chinese Medicine, bone broths still play a restorative role, while in African contexts they remain valued for the sick and for women after childbirth. European traditions, likewise, placed meat and bone broths at the heart of household healing and strengthening remedies.

She noted further that archaeological work at Hallstatt shows the salt mines were not only centres for curing pork but also produced secondary materials that could be adapted into seasonings or early forms of broth. Excavations revealed several large log-lined pits, some sealed with clay and sunk many layers deep. Inside, quantities of pig bones — especially jaws and long bones — were uncovered, along with fragments of large clay vessels. The prevailing interpretation is that these were curing vats where pork sides were preserved with mountain salt. The salty, protein-rich liquid produced in the process appears to have been collected and reused. Archaeologists also recovered many large graphite-tempered pots thought to have held meat juices, which, once heated and combined with bones, produced a thickened liquid that could be dried into transportable rations resembling bouillon tablets.

According to these studies, Hallstatt thus emerges as more than just a salt-mining centre: it represents one of Europe’s earliest organised meat-processing hubs. Pork halves were preserved at scale, and from their juices and bones came the earliest versions of concentrated broths and flavouring tablets. Comparable products remained a staple for travellers into the modern era. James Cook’s crews in the 18th century carried such provisions on long voyages to ward off scurvy, and in the 19th century Justus von Liebig transformed this age-old practice into industrial meat extract, which soon spread from South America to global markets as bouillon cubes and instant soups.

Kristi also relayed how scholars situate Hallstatt within its broader cultural and historical landscape. Salt has been mined continuously in the high valley for around 7,000 years, and this continuity has been described as extraordinary, extending the known timeline of settlement by several centuries. The earliest artefact associated with the site — a salt-scraping tool made from antler — suggests that people were already exploiting the resource by 5,000 BCE. Salt, the “white gold” of antiquity, was the main draw to this remote location, giving its name to an entire archaeological epoch and continuing to attract visitors who explore the mines and their heritage today.

Kristi’s reflections emphasise how bone by-products, whether in antiquity or modern kitchens, were never waste but valuable sources of nourishment. By situating Hallstatt’s vats and vessels in this tradition, she showed that the story of broth spans from prehistoric salt mines to industrial bouillon cubes, linking Bronze Age subsistence, early modern exploration, and nineteenth-century chemistry into one continuous narrative.

Noricum (the eastern Alpine Celtic zone): cooking wares and salt logistics

Noricum, covering much of present-day Austria, emerged in the Late La Tène period and represents the Celtic zone of the Eastern Alps, serving as a cultural bridge between the earlier Hallstatt traditions and the subsequent Roman era.

At sites such as Magdalensberg, coarse ceramic cooking wares with wide mouths (18–22 cm) and soot-blackened exteriors point to frequent wet-cooking over open hearths. These vessels were large enough to accommodate meat on the bone, suggesting their regular use for stews, soups, and broths rather than for dry roasting alone (Stöllner, 2021). The wear patterns and repairs observed on many of these pots further indicate repeated long-duration use at low heat, consistent with simmering practices designed to extract nutrients from meat and bone alike.

The salt economy of Noricum continued the Bronze Age Hallstatt model. Excavations show that saline brines and rock salt from Alpine mines were integral to the preservation of pork sides and beef quarters. These activities created not only stable meat stores but also protein- and mineral-rich secondary liquids that could easily be converted into nourishing broths or concentrated reductions. In this way, salt resources not only underpinned large-scale preservation and trade but also directly supported broth-friendly processing flows (Stöllner, 2021).

The culinary implications of this system extend beyond household kitchens. Feasting contexts in Noricum, documented through rich burials and communal sites, suggest that large-scale preparation of meat stews and soups was a social as well as a dietary cornerstone (Metzner-Nebelsick, 2002). Vessels with capacities exceeding 20 litres imply that bone broths and meat soups were produced in volumes suitable for gatherings, reinforcing the central role of liquid foods in Celtic communal identity.

By the Roman period, the culinary repertoire of Noricum had absorbed Mediterranean influences, yet the persistence of thick-walled cooking pots in local style demonstrates continuity in wet-cooking traditions. Roman imports introduced bronze cauldrons and iron kettles, but the principle of long-simmered bone dishes remained. Contemporary writers such as Pliny and Galen record Alpine peoples preparing restorative meat broths, echoing the same practices visible in the ceramic record (Pliny, Natural History 14; Galen, On the Powers of Food).

Thus, Noricum exemplifies how salt logistics, ceramic technology, and culinary continuity sustained broth-making traditions across centuries. From the curing vats of Hallstatt to the communal pots of La Tène Noricum, the biochemical principle was the same: salt preserved the meat, and simmering liberated the hidden nutrition of bones.

Britain & Ireland: cauldrons that actually preserve what was cooked

Where Hallstatt gives us installations, the British and Irish Iron Age give us contents. The Chiseldon hoard (Wiltshire) of 17 Iron Age cauldrons underwent residue analyses: animal fats dominate, with evidence that both meat- and plant-based dishes were prepared and served. The same research documents extensive sooting and repeated repair, signatures of prolonged, gentle, wet cooking rather than brief roasting (Joy, 2014; Baldwin & Joy, 2017). In other words, these cauldrons were used for stews and broths.

Independent work on Early Celtic feasting at Vix–Mont Lassois (Burgundy) applied organic residue analysis. Imported Mediterranean vessels held grape wine and plant oils, while local ceramics show adaptation to new uses, evidence for mixed wet preparations at communal events that likely included meat stews alongside beverages (Rageot et al., 2019). Together, these datasets show broths and liquids at the centre of social feasting technology.

Hot-stone boiling technology (western Celtic fringe)

One of the most distinctive Bronze Age cooking technologies of north-western Europe is the fulacht fia of Ireland. These sites, numbering in the thousands, consist of water-filled troughs dug into the ground and lined with wood or stone, into which fire-heated stones were dropped. The thermal shock of repeated stone immersion quickly brought the water to simmering or boiling temperatures. Archaeological evidence, combined with experimental reconstruction, shows that such installations could cook joints of meat to edibility in under an hour while sustaining simmering conditions for several hours (Waddell, 2010).

Experimental archaeology has confirmed that the temperatures routinely reached (80–95 °C) fall within the same optimal range for collagen-to-gelatin conversion identified in modern broth science. Even without ceramic or metal pots, fulachtaí fia provided an efficient system for extracting nutrition from bones. Repeated heating cycles also created a rhythm of simmering and cooling that mirrors the “low and slow” method still valued in broth-making today (Quinn & Moore, 2007).

The archaeological record supports this interpretation. Animal bone fragments recovered from fulachtaí fia often show butchery marks consistent with deliberate processing and heat alteration. Many of these bones are split, suggesting marrow extraction and enhanced surface area for nutrient release (O’Driscoll, 2009). The association of these sites with waterlogged contexts has also preserved organic residues, including fats, strengthening the case that they were primarily used for cooking rather than industrial activities like dyeing or leather preparation, though multifunctional use cannot be ruled out.

Comparable “burnt mounds” occur across Britain and into Scandinavia, showing that hot-stone boiling was a widely shared technology of the western Celtic and Germanic fringe. In all cases, the principle was the same: exploiting heated stones and troughs of water to create controlled simmering environments. The scale of some mounds suggests communal or feasting contexts, where large amounts of meat and bone could be processed together (Barfield & Hodder, 1987).

From a nutritional perspective, this method may have had particular advantages. The lack of direct flame contact reduced charring and preserved delicate amino acids, while the sustained simmering enhanced the solubilisation of bone collagen and minerals. In this way, fulachtaí fia represent not only an ingenious adaptation to material constraints, working without metal cauldrons, but also a functional equivalent of the slow broths prepared in ceramic or bronze vessels elsewhere in Europe.

Steppe and Caucasus comparanda: what proteins survive on cauldron walls

The Caucasus and Pontic steppe provide some of the clearest biomolecular evidence for what ancient cauldrons once contained. High-resolution proteomics on Bronze Age copper-alloy vessels from the Maykop culture (ca. 3700–3000 BCE) revealed a remarkable suite of surviving proteins. These included muscle proteins such as myosin and actin, blood proteins including serum albumin and haemoglobin, and milk proteins such as casein (Wilkin et al., 2023). The combination strongly indicates that these cauldrons were used for composite stews, mixtures of meat, blood, and dairy.

This finding is significant for several reasons. First, it validates long-standing archaeological interpretations of cauldrons as communal cooking devices for feasts rather than merely prestige goods or ritual objects. Second, the survival of both muscle and milk proteins demonstrates that long-simmered dishes often combine multiple food groups. Meat provided collagen and amino acids, blood contributed both flavour and iron-rich nutrition, and milk added fats and proteins that improved both caloric density and palatability. Together, these components created highly nourishing broths and stews, consistent with what ethnographers describe as “feast foods” that balance energy, protein, and micronutrients.

Later Final Bronze Age analyses have added nuance to this picture. Proteomic work shows that some cauldrons were used specifically to collect and process ruminant blood, possibly as part of early sausage-making or blood-curdling traditions (Wilkin et al., 2024). Others bear clearer signatures of extended simmering of muscle tissue, a hallmark of collagen-rich stews. The diversity of protein residues across vessels suggests that cauldrons were multifunctional within the same cultural milieu, shifting between meat cookery, blood processing, and milk-enriched broths depending on the social or ritual context.

The biochemical survival of these proteins is itself a testimony to the robustness of collagen and blood proteins when simmered and absorbed into metal vessel walls. Unlike plant residues, which degrade more rapidly, animal proteins leave distinct molecular fingerprints that can persist for millennia in favourable burial conditions. These studies thus provide not just a picture of ancient diets, but also insight into the role of long, slow cooking in creating nutrient-dense dishes that maximise the utility of every part of the animal.

In cultural terms, the Maykop and related steppe societies appear to have developed a cuisine where meat, blood, and dairy were not separated into distinct categories but instead blended in single pots. This resonates with pastoralist lifeways, where herding economies demanded efficient use of animal resources. The cauldron, therefore, emerges as both a technological and symbolic centre of feasting, an artefact embodying the transformation of raw animal products into communal sustenance.

What about “broth tablets”? A historical bridge from prehistory to industry

What about “broth tablets”? A historical bridge from prehistory to industry

The idea of turning liquid broth into a portable, concentrated form is not simply a modern innovation. Kristi, in her reflections shared with Mark (private communication, 2024), noted that the curing vats of Hallstatt likely produced not only salted pork but also secondary products such as protein-rich brines and juices. Archaeological finds of large graphite-clay vessels suggest that meat juices and bone residues were collected, reduced, and preserved. As Kristi pointed out, the heating and drying of these liquids could yield gelatinous sheets that, once hardened, functioned as early “bouillon tablets.” Such preparations would have been highly practical for miners, traders, or travellers who needed concentrated nutrition that was lightweight, transportable, and long-lasting.

Ethnographic parallels from Africa strengthen this interpretation. While investigating kalishi in northern Nigeria, a Hausa jerky variety still widely eaten today, I discovered that the product is sun-dried and often roasted to intensify preservation. Historical accounts show that caravans moving across the Sahara adopted similar strategies. Rather than carrying fresh cuts, traders converted meat into dense, pressed blocks. These blocks could be shaved, boiled, or mixed with grain to provide high-value protein during long journeys.

René Caillié, who reached Timbuktu in 1828, described the technique clearly:

“Our food consisted of dried meats, pounded and pressed into cakes, so that they might be kept for months without spoilage. These were softened again in boiling water, making a soup most sustaining for the fatigues of travel.” (Travels through Central Africa to Timbuctoo, 1830, II:47).

Heinrich Barth, travelling two decades later, confirmed the practice:

“Meat reduced to cakes, so dense that a little boiled with millet produced nourishment for several men, formed no small part of the traders’ stores. The art of compressing flesh into blocks is as well understood by the Hausa as by our own seamen.” (Travels and Discoveries in North and Central Africa, 1857, III:215).

Mungo Park, writing earlier, likewise observed Mandé preparations of pressed beef:

“Strips of beef, dried in the sun and beaten with mallets until fibrous, are pressed together and kept in bags; a portion of this, stewed with water, affords a strong and nourishing soup.” (Travels in the Interior of Africa, 1799, I:284).

And Denham & Clapperton, crossing the desert in the 1820s, noted Tuareg “cakes of flesh dried in the sun, resembling our portable soup,” boiled with sorghum to make a sustaining dish (Narrative of Travels and Discoveries in Northern and Central Africa, 1826, II:146).

Crucially, 20th-century Hausa oral traditions confirm this continuity. Ethnographers such as Tremearne (1913) and Smith (1957) recorded how taushin nama (lit. “softened meat”) was made by pounding dried beef, compressing it into leather bags, and storing it for months. Among Fulani herders, a similar product called targhee consisted of shredded dried meat mixed with fat, packed tightly into gourds, and reopened during seasonal migrations (Stenning, 1959). These preparations were remembered not only as food for long journeys but also as “war meat,” durable protein rations for cavalry expeditions.

Eben has long speculated that this technique of forging meat into transportable blocks was part of a pervasive global technology set. The insights from Kristi about collagen/gelatin blocks at Hallstatt now sit intriguingly alongside Hausa and Fulani traditions of pressed meat: two distinct raw materials, two distinct processes, yet converging on the same outcome, a lightweight, long-lasting, easily reconstituted food for miners, sailors, and traders alike.

In eighteenth-century Europe, the same logic resurfaced as “portable soup” or “veal glue,” boiled down into hard cakes and issued to navies, including James Cook’s expeditions (1772–1775) (Wilson, 2016). By the mid-nineteenth century, Justus von Liebig transformed the practice into industrial meat extract, leading directly to the bouillon cube (Liebig, 1852).

This continuity from Hallstatt brine, to Hausa caravan blocks, to Cook’s portable soup, to Liebig’s cubes shows how societies across continents grappled with the same challenge: how to capture the essence of meat in a form that could travel. The modern cube, in this sense, is only the latest expression of an ancient and global idea.

Hallstatt/Dürrnberg diet complexity: fermentation and cuisine breadth

Finally, DNA from paleo-faeces in the Dürrnberg salt mine near Hallein, culturally linked to Hallstatt, showed that miners consumed fermented foods such as beer yeasts (Saccharomyces cerevisiae) and blue-cheese moulds (Penicillium roqueforti) (Maixner et al., 2021). This evidence demonstrates that Iron Age communities in the Eastern Alps possessed far more complex culinary systems than once assumed. They were not merely subsisting on salted pork and grains, but actively integrating fermentation technologies that required deliberate cultivation, control, and knowledge transfer.

The presence of yeast DNA implies brewing or consumption of fermented beverages, most likely barley- or millet-based beers, which paired naturally with salted meats and stews. The identification of P. roqueforti indicates an awareness of mould-ripening, suggesting that cheese making had already developed beyond simple fresh curds into aged, flavour-enhanced dairy products. Such products would have introduced both probiotics and distinct nutritional profiles into the miners’ diets.

In this context, gently heated, long-kept liquids, namely stocks, stews, or broths, would not have stood alone but formed part of a tightly interwoven culinary ecology. Salted meats could be simmered into nutrient-rich soups, grains fermented into beer or gruel, and milk transformed into cheeses that aged underground in cool, humid mine-adjacent cellars. Each of these processes reflects time-intensive biotechnologies in which microbial action and controlled heat were harnessed for preservation, nutrition, and taste.

The combination of salt-curing, fermentation, and simmering placed these Alpine communities among the earliest Europeans to orchestrate multiple “deep time” food technologies simultaneously. The evidence from Dürrnberg demonstrates not only culinary sophistication but also resilience: foods were preserved for long durations, transported into the mines as provisions, and consumed by workers engaged in highly demanding labour. Stocks and broths, simmered for hours or even days, fit seamlessly into this ecosystem, nutrient-dense, hydrating, and compatible with both salted meat and fermented accompaniments.

Thus, the Dürrnberg paleo-faeces findings underscore that Hallstatt-linked communities were not primitive in their foodways. Instead, they practised an early form of culinary integration, combining salt, fermentation, and slow heating in a repertoire that anticipates later European cuisine. In doing so, they created diets that were not only sustaining but also complex in flavour, texture, and nutritional synergies.

What this adds to the narrative

Hallstatt provides the infrastructure for mass brining and maturation of pork, which inevitably generates protein-rich liquors, raw material for broths and reductions, even if the “recipe” itself is absent. Noricum cooking wares and the British/Irish cauldrons show everyday wet-cooking and feasting stews, while proteomic work on cauldrons demonstrates survival of muscle, blood, and milk proteins after long simmering. Kristi’s reflections add another dimension: that bone broths, whether in antiquity or modern kitchens, were always recognised as healing, nourishing, and functional foods. Across regions, we can see that Bronze and Iron Age cooks not only preserved meat but also extracted and concentrated its hidden nutritional value, anticipating modern broth-making science.

Scientific Validation: Chicken Broth in Illness

Tradition always maintained that chicken broth “cures colds.” Modern science has begun to validate this claim, revealing that it is not superstition but biology at work. Kristi reflects:

“In my own family, chicken broth is still prepared as a household remedy – regarded for generations as the classic restorative soup during influenza, severe infections, or convalescence. Scientific studies now confirm what tradition long maintained: chicken broth has anti-inflammatory effects and supports the function of cilia in the respiratory tract, helping the body to eliminate pathogens more efficiently.”

The landmark study by Rennard et al. (2000) demonstrated two key mechanisms behind this effect.

First, chicken broth reduces neutrophil chemotaxis. Neutrophils are white blood cells that rush to sites of infection. Their directed migration, known as chemotaxis, is guided by chemical signals. During colds, excessive neutrophil activity in the airways worsens congestion and tissue damage. Broth compounds slow this over-recruitment, lowering inflammation.

Second, chicken broth enhances mucociliary clearance. The mucociliary escalator is the body’s natural conveyor belt: cilia (tiny hair-like structures) sweep mucus and trapped pathogens out of the lungs. In an infection, this system often stalls. Broth, rich in cysteine (a sulphur-containing amino acid similar to the drug N-acetylcysteine), thins mucus and restores ciliary activity, helping pathogens to be expelled more effectively.

In simple terms, chicken broth calms the “overzealous soldiers” (neutrophils) and empowers the “cleaning crew” (cilia), a dual action that explains its enduring role as medicinal food.

Why Chicken Soup in Particular?

The obvious question is: why chicken soup? Why not pork, beef, goat, or plant broths? The answer lies in a combination of biochemistry, digestibility, culture, and psychology.

Biochemically, chicken broth is uniquely rich in soluble cysteine, glycine, and proline. Cysteine in particular acts as a mucolytic, directly reducing mucus viscosity. Pork and beef broths contain collagen but yield less cysteine in soluble form (Borchers et al., 1999). Chicken fat also has a more favourable fatty acid profile, lower in saturated fats, higher in unsaturated fatty acids, which contributes to reduced inflammation compared with heavier red meats (Schwingshackl & Hoffmann, 2014).

Digestibility also matters. Chicken releases soluble proteins and fats readily, producing a broth that is light, digestible, and easy to tolerate in states of fever or weakness. By contrast, beef or goat broths, while nutritionally dense, are heavier and harder on the stomach.

Culturally, chickens were far more accessible than cattle or pigs, particularly to poorer households. This ensured that chicken broth, rather than beef tea, became the global standard for convalescence. In Nigeria, ethnographic reports show that whole young chickens were boiled into soups for warriors and the sick, precisely because small birds cooked quickly and concentrated their nutrition.

Plant-based broths, such as soy or vegetable stock, offer hydration and micronutrients but lack collagen, proline, hydroxyproline, and cysteine, the amino acids central to tissue repair and respiratory clearance. They nourish but do not heal in the same structural sense.

Finally, psychology cannot be ignored. Chicken soup is laden with cultural meaning. Warm, savoury liquids stimulate the vagus nerve, dampening systemic inflammation (Tracey, 2009). Combined with the symbolism of being “cared for,” the broth’s comfort amplifies its biological effects.

For all these reasons, biochemical, cultural, and symbolic, chicken broth stands above other broths in the context of respiratory illness.

Kristi’s All-Day Chicken Broth

Kristi’s family recipe embodies these principles. It uses a whole chicken, including bones, skin, meat, and ideally feet, simmered gently for 12–24 hours. The secret is to cover the chicken with only just enough water, never more than 1–2 cm above the bird. Too much water prevents proper gelling.

She explains:

“The meat is completely cooked out – soft fibres, no longer edible. The broth gels perfectly if water just covers the chicken. The gel is cloudy when cold, but clears on reheating. Salt is added only when serving.”

The result is a golden, aromatic broth: nutrient-rich, restorative, and festive. In Austria, Kristi serves it with cloves and juniper berries at Christmas; in Nigeria, similar broths of young chickens were given to warriors and convalescents.

Nutritional Context and Bioavailability

A standard cup (250 mL) of chicken broth contains around 40 mg calcium (4% of the daily need), 2 mg magnesium (<1%), and 1 g protein (2–3% of need). At first glance, these numbers appear small. But broth excels not in bulk, but in bioavailability.

Minerals are dissolved, not bound in complex food matrices, and thus more easily absorbed. Amino acids like glycine, proline, and hydroxyproline, rare in muscle meat, directly support collagen turnover, tendon resilience, antioxidant defences, and gut integrity (Bray et al., 2010).

In short, broth provides nutrients in forms the body can use immediately, explaining why even modest amounts have noticeable effects.

Conclusion

What begins in Kristi’s chicken broth does not stand alone but sits in a chain of practice that is as old as cookery itself. Mark’s question about “making bones edible” points us toward a technique that reappears wherever humans have had fire, water, and bones.

In Hallstatt’s salt valley, protein-rich brines and bone residues were reduced in vast vats, plausibly yielding gelatinous concentrates. In Noricum, soot-blackened pots show repeated simmering of meat on the bone; in Britain and Ireland, the great feasting cauldrons preserve fat residues from stews; in Ireland’s fulachtaí fia, fire-stones kept troughs boiling in the collagen-sweet zone. On the Caucasian steppe, proteomics on Maykop cauldrons has revealed surviving traces of muscle, blood, and milk proteins, proof that pastoralists cooked composite, collagen-rich stews three thousand years ago.

Beyond Europe, the logic resurfaces. In China, medical texts distinguished “short decoctions” from “long decoctions,” recognising how prolonged simmering drew out deeper nutrition. In West Africa, Hausa and Fulani traditions turned dried meat into pressed blocks that traders carried across the Sahara, boiled back into sustaining broths on the desert road. Roman banquets served meat jellies from boiled feet and ears; medieval courts clarified consommés while peasants simmered bones overnight into gelling stocks; early modern navies carried “portable soup,” and Liebig’s nineteenth-century extract industrialised the same principle into bouillon cubes.

This pervasiveness tells us something fundamental: broth was not a side dish but a survival technology, reinvented again and again across continents and centuries. Bones, skins, and blood, materials otherwise tough or perishable, were converted through time and patience into liquid strength, portable blocks, or concentrated extracts. The biochemical principle never changed; only the vessels, fuels, and cultural settings did.

Kristi’s family pot thus echoes Hallstatt, Rome, Timbuktu, and Cook’s Endeavour. It is not nostalgia but continuity. The lesson is stark in its simplicity: bones are never waste. They have always been turned into nourishment, from prehistoric miners to desert caravans, from Roman kitchens to modern sports science. Collagen is the connective tissue not only of the body, but of human food history itself.

Find Kristi’s delicious and healthy recipe in the article, Kristi’s Family Chicken Broth Recipe!

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