How to Manufacture Gelatin and Glue from Bones

Gelatin is one of those substances hiding in plain sight – in your desserts, your medicine capsules, your photo prints, and the joints of antique furniture. Yet most people have no idea it starts as animal bones. The process of manufacturing gelatin and glue from bones is a well-established industrial practice that converts slaughterhouse by-products into high-value commercial products. Understanding how this works – from raw bone to finished product – reveals just how efficiently the animal processing industry can utilize what would otherwise be discarded waste.

What are gelatin and glue, and how are they related? 🔗

According to the Gelatin Manufacturers Institute of America, gelatin is produced by the partial hydrolysis of collagen – the chief structural protein found in the connective tissue, skin, and bones of animals. It does not occur freely in nature, and importantly, it cannot be recovered from horns, hoofs, or other non-collagen-containing parts of vertebrate animals. Glue, on the other hand, is an adhesive made from the same collagen-rich raw materials through a similar but less refined process. It contains two key protein groups: chondrin, which provides adhesive strength, and glutin, which contributes gelling strength and tackiness.

The essential difference between gelatin and glue is one of purity and grade. Gelatin glue is fully processed and purified, while bone glue – made from bone waste, cartilage, and tendons – undergoes a rougher process, resulting in more impurities and batch-to-batch variation. Colour is a reliable indicator: the darker the product, the lower the grade.

Raw material selection and preparation 🔗

Only high-quality raw materials from the meat industry are used in gelatin and glue production. The primary sources are cattle bones, cattle hides, and pork skins. Approximately 40% of edible gelatin produced worldwide comes from pork skins, while the remaining share is split between cattle hide splits and connective tissues from cattle, pigs, poultry, and fish.

Bone selection is the first critical step. Fresh or recently processed bones from slaughterhouses are preferred, as deteriorated material negatively affects product quality. Once collected, the bones are cut or crushed into smaller pieces – typically around 1-2 mm in industrial grinding operations – to increase surface area and improve extraction efficiency. The fat content must be reduced to below 1% before the main extraction step, so bones are degreased by soaking in hot water or using solvents.

The manufacturing process: step by step 🔗

Step 1 – Degreasing and washing 🔗

Raw bones arrive at the processing facility, are inspected for quality, and are loaded into cutting or crushing machines. They are then passed under high-pressure water sprays to remove debris, followed by soaking in hot water to bring fat content down to approximately 2%. This stage is critical because excess fat interferes with collagen extraction and reduces the clarity of the final gelatin.

Step 2 – Demineralisation (for bones) 🔗

Bones are treated with dilute hydrochloric acid to dissolve calcium and other mineral salts. The resulting sponge-like, collagen-rich material is called ossein. This demineralisation step is specific to bone-based production and is what makes bone processing more involved than hide-based gelatin manufacturing. The acid treatment typically takes several hours, after which the ossein is rinsed and neutralised.

Step 3 – Pretreatment: acid or alkali conditioning 🔗

Two main pretreatment methods are used depending on the raw material and the type of gelatin required. The acid process – developed in the USA in the 1930s – is primarily suitable for pork skin and involves soaking in acid for a relatively short time, producing Type A gelatin. The alkaline (liming) process treats ossein and cattle hides in lime solution at ambient temperature for anywhere from 5 to 20 weeks – this breaks down cross-linked collagen more thoroughly and yields Type B gelatin, which is the standard for pharmaceutical and photographic applications.

Step 4 – Hot water extraction 🔗

After pretreatment, the conditioned material undergoes multi-stage hot water extraction. Hot water is combined with raw materials at carefully controlled temperatures – the temperature used directly determines the gel strength, or Bloom value, of the finished gelatin. Lower extraction temperatures yield gelatin with a higher Bloom value (stronger gel), while higher temperatures produce weaker, lower-grade gelatin. Multiple extraction cycles are carried out at gradually increasing temperatures, ranging from 50°C to near boiling, to maximise yield.

The heat treatment breaks hydrogen and covalent bonds within collagen’s triple helix structure, causing what is known as a helix-to-coil transition – converting insoluble collagen into soluble gelatin. Total gelatin yield typically ranges from 12% to 15% of the raw material’s wet weight, with the remainder converted into fat, protein feed, or fertiliser-grade residues.

Step 5 – Filtration, evaporation, and purification 🔗

The extracted gelatin solution is filtered through high-quality separators to remove fat traces, fine fibres, and undissolved solids. It is then concentrated through evaporation under controlled conditions. The highly concentrated gelatin solutions are sterilised, cooled, set, and dried under strict hygienic conditions, producing what are known as “jelly noodles,” which are then ground into grains or powder after drying. Throughout this process, strict adherence to Good Manufacturing Practices and HACCP programs ensures product purity and compliance with international standards.

How glue manufacturing differs from gelatin production 🔗

Bone glue follows the same fundamental steps – crushing, washing, lime soaking, boiling, and drying – but without the extensive purification stages that define pharmaceutical or food-grade gelatin. The manufacturing process for glue consists essentially of washing the stock, crushing or shredding the bones, soaking in lime solution to remove flesh residues, boiling to extract the gelatinous material, gelling, and finally drying.

Bone glue is produced by a thermal extraction process and hot water treatment of animal connective tissue protein, with degreased slaughterhouse bones as the standard raw material. The resulting product is a natural, light to yellowish-brown adhesive that is extremely strong but brittle in its dry form. After heating and processing, collagen is converted into a water-soluble form with adhesive properties – importantly, this bond can be reactivated with heat, a property that makes animal glue especially valuable in restoration work.

For glue applications, animal glue naturally contains two types of proteins: chondrin, which increases bonding strength, and gluten (protein-based, not wheat gluten), which increases gelling strength for tackiness and hardness. Plasticisers such as glycerin or sorbitol are often added to improve elasticity, particularly for bookbinding applications where flexibility is needed.

Types and grades of gelatin 🔗

Industrial gelatin is classified by its source, processing method, and functional properties. The two main types are Type A, derived from acid-processed raw materials (typically pork skin) with an isoelectric point around pH 9, and Type B, derived from alkaline-treated raw materials (usually bovine hides or bones) with an isoelectric point around pH 5. Bloom strength – the measure of gel firmness – typically ranges from 30 to 300 grams; higher Bloom numbers are required for pharmaceutical and food-grade applications.

Glue is similarly graded. Bone glue is dark red in colour, button glue is slightly lighter, and hide glue lighter still – colour being a reliable proxy for purity. Gel strength and viscosity are the two most commonly used parameters for determining the commercial grade of a glue batch.

Applications of gelatin across industries 🔗

Food industry 🔗

Gelatin is widely used in the food industry as an ingredient to improve the elasticity, consistency and stability of foods. Common applications include confectionery (gummy bears, marshmallows, jelly babies), dairy products such as yoghurt and ice cream, meat products, and clarifying agents in beer and wine production. Its cold-setting, thermoreversible nature – gelling below body temperature and dissolving on gentle heating – gives it functional advantages over plant-based gelling agents like carrageenan or agar.

Pharmaceutical industry 🔗

The pharmaceutical sector is the second-largest consumer of gelatin after food manufacturing, using it primarily for hard and soft capsules that protect active ingredients from moisture and light while masking unpleasant tastes. Gelatin is also used in tablet coatings, plasma expanders, vaccine adjuvants, wound dressings, and biomedical scaffolds. Its biocompatibility and biodegradability make it a preferred excipient in drug delivery systems.

Photographic industry 🔗

The use of gelatin in photographic emulsions dates back to about 1870, when it replaced the older collodion wet process. In photographic films and papers, gelatin suspends silver halide crystals in emulsion layers, enabling high-resolution imaging. Type B alkaline-processed gelatin from ossein remains the standard for photographic applications, with properties carefully controlled to achieve specific levels of sensitivity and clarity.

Industrial and adhesive applications 🔗

Animal glue – produced from bones and hides – is an adhesive created through prolonged boiling of connective tissue in a process called rendering. It is used for coating and sizing, decorative ornaments, and as a clarifying agent. Bone glue is widely used in woodworking, carpentry, restoration, bookbinding, and musical instrument manufacturing, where its reversibility – the ability to be reactivated with heat and moisture – is a key advantage over synthetic adhesives. In the paper industry, gelatin strengthens paper fibres, reduces ink bleed, and improves print quality. It also serves as an adhesive in plywood production and as a mordant in textile dyeing to improve colour fastness.

Environmental and safety considerations 🔗

Gelatin manufacturing generates high organic-matter wastewater with elevated biological and chemical oxygen demand, and releases odorous compounds during bone processing. Responsible manufacturers use activated sludge treatment and biological wastewater systems to manage these outputs. By-products such as tallow and bone ash are typically recovered and reused, supporting resource efficiency aligned with circular economy principles.

On the safety front, concerns about bovine spongiform encephalopathy (BSE) led to significant regulatory review. The EU’s Scientific Steering Committee stated in 2003 that the risk associated with bovine bone gelatin is very low or zero, a position confirmed by the European Food Safety Authority in 2006. Producers must comply with standards set by the FDA, EFSA, and equivalent bodies, with pharmaceutical-grade gelatin further required to meet Good Manufacturing Practice and traceability requirements.

Gelatin vs. glue: a summary of key differences 🔗

Though manufactured through broadly similar processes, gelatin and bone glue are distinct products serving different markets. Gelatin is a high-purity, food-safe protein product used in food, medicine, and photography. Bone glue is a lower-grade, less purified adhesive valued for its bonding strength, reversibility, and biodegradability in woodworking, restoration, and paper industries. The core distinction lies not in the raw material – both come from collagen in animal bones and connective tissues – but in the degree of processing, purification, and the functional specifications required by their respective end uses.

Both products share an important common characteristic: they represent the efficient conversion of animal by-products into commercially valuable materials, reducing waste from the meat and leather industries while supplying ingredients that remain difficult to replicate synthetically at equivalent quality and cost.

What do you think? Given that gelatin and bone glue are derived from the same raw material through different levels of processing, should industrial facilities producing one product routinely integrate the production of both – and what operational or regulatory challenges might that create? And with growing consumer demand for plant-based alternatives, how do you see the role of bone-derived gelatin and glue evolving in food and pharmaceutical manufacturing over the next decade?

References

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