FOOD CHEMISTRY: GELLING AGENTS
Diagram
Two gelling agents, two sources
Agar
From seaweed. A polysaccharide. Sets firmly on cooling and needs strong heat to melt again.
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Gelatin
From animal collagen. A protein. Sets into a soft gel and melts at mouth temperature.
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Use
Both turn a liquid into a gel, but they give different textures and melt in different ways.
Figure 1: Agar comes from seaweed and gelatin comes from animal collagen. Drawn in our own style from the gelling agents covered in Edwards, The Science of Sugar Confectionery.
Introduction
Agar and gelatin are both gelling agents, and both turn a liquid into a jelly, but they come from different sources and behave differently. Agar is a polysaccharide taken from seaweed. Gelatin is a protein made from animal collagen. That difference in chemistry decides how firm the gel is, how it melts, and which foods each one suits.
Edwards covers agar, gelatine, gellan gum and pectin together as the gelling agents of sugar confectionery. This article follows that book.
Quick comparison
Table 1: Agar compared with gelatin
| Aspect | Agar | Gelatin |
|---|---|---|
| Source | Seaweed | Animal collagen, from skin and bones |
| Chemical type | Polysaccharide | Protein |
| Setting | Sets firmly on cooling into a firm, brittle gel | Sets into a soft, elastic gel |
| Melting | Needs much higher heat to melt again once set | Melts at mouth temperature, so it melts as it is eaten |
| Texture | Firm and brittle, cuts cleanly | Soft and wobbly, melts in the mouth |
| Clarity | Gives a clear gel | Gives a clear gel when pure |
| Use in heat | Holds its shape in hot food | Melts in hot food |
| Amount needed | A small amount sets a large volume of liquid | More is needed for the same firmness |
| Suitable for vegetarians | Yes, it comes from seaweed | No, it comes from animals |
| Typical foods | Jellies, Asian desserts, microbiology plates, confectionery | Jellies, marshmallows, gummy sweets, desserts |
Scientific explanation
Definition
Agar is a polysaccharide gelling agent extracted from seaweed. It dissolves in hot water and sets into a firm gel on cooling. Gelatin is a protein gelling agent made by breaking down animal collagen. It dissolves in warm water and sets into a soft, elastic gel on cooling, and that gel melts again at mouth temperature.
Working principle
Agar chains dissolve in boiling water and, as the solution cools, they join into a network that traps water, giving a firm gel that stays solid until it is heated strongly again. Gelatin chains also form a network on cooling, but the network is held by weaker links, so it melts at mouth temperature. That is why a gelatin jelly melts in the mouth while an agar jelly keeps its shape and must be chewed.
Apparatus
The books used here name no laboratory apparatus for telling the two apart, so no apparatus list is given.
Measurement procedure
The books used here name no single standard laboratory procedure for telling the two apart. The distinction is made from the definitions and properties given above, not from one test.
Factors affecting readings
Concentration decides firmness: more gelling agent gives a firmer gel. Sugar, acid and salt change how the network forms. Heating time matters: agar must be boiled to dissolve fully, while gelatin must not be boiled hard or its protein network weakens. Cooling rate changes the texture of the finished gel.
Formulas and calculations
The books used here give no formula for this comparison, so no formula or worked calculation is given.
Industrial applications
- Agar is used in jellies, Asian desserts, and sugar confectionery where a firm set is wanted.
- Gelatin is used in marshmallows, gummy sweets and desserts where a soft melt is wanted.
- Agar is used in microbiology plates because its gel stays solid at warm temperatures.
- Gelatin is used in confectionery to give chew and to hold air in foams.
- Both are used to set fruit jellies and moulded desserts.
Advantages and limitations
- Agar: advantage: sets firmly and holds its shape in warm food. Limitation: the gel is brittle and does not melt in the mouth.
- Gelatin: advantage: melts in the mouth, giving a smooth eating quality. Limitation: melts in hot food, so it cannot hold shape when warm.
- Agar: advantage: suitable for vegetarian food. Limitation: needs boiling to dissolve, so it is less convenient in cold preparation.
FAQ
Can agar replace gelatin in a recipe?
It can set the liquid, but the texture will be firmer and it will not melt in the mouth, so the amounts and the result differ.
Why does a gelatin jelly melt on the tongue?
Gelatin is a protein network that melts at mouth temperature, so body heat is enough to melt it.
Is agar vegetarian?
Yes. Agar comes from seaweed, while gelatin comes from animals.
Which one sets firmer?
Agar sets much firmer than gelatin at the same kind of use.
