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The Science of Carrageenan – Thickening/Gelling Foods with Seaweed

Have you also noticed that a lot of store bought chocolate milks do not split whereas in your homemade chocolate milk the cocoa powder sinks down in a matter of minutes? Have you wondered how store bought ice cream is so stable for long periods of time?

A quick look on the pack of these and a lot of other products will show you that they contain carrageenans (in the EU identified by E-number E407). They are one of the many food additives allowed in our foods and are mostly used for thickening and stabilizing foods like chocolate milk and ice cream. But did you know they originally come from seaweed? And did you know there are actually different types of carrageenan?

That’s why it’s time for a deeper dive into some carrageenan science.

What is carrageenan?

Carrageenans are polysaccharides. Polysaccharides are large saccharides made out of a lot of linked monosaccharides. Carrageenans chains are linear, meaning they do not branch out, it is just one long strand of molecules. In the case of carrageenans these molecules are galactose and 3,6-anhydrogalactose.

Linked to this long chain of molecules are sulfate groups. These groups contain a sulphur atom and 4 oxygen atoms attached to the sulphur. These sulphate groups can sit at different positions on the galactose molecules and the number of sulphate groups per molecule differs as well. This distribution and number of groups is what greatly impacts the functionality and type of carrageenan.  The amount of sulphate groups has a big influence on the behaviour of the carrageenan. Since the sulphate groups are negatively charged, they influence the behaviour of the carrageenans significantly. Negative charges repel one another, whereas they are attracted to positive charges. This is how they form certain structures and conformations.

How is carrageenan made?

Carrageenan is naturally present in seaweed so manufacturing mostly exists of removing the carrageenan from the seaweed. Not all seaweed types are suitable for carrageenan manufacturing. After harvest the seaweed is cleaned. If it is not used immediately it is dried, in warm climates manufacturers simply use the sun to do so. As a next step manufacturers extract the carrageenan using an alkaline solution (=opposite of an acidic one). This treatment will influence the quality and type of carrageenan that it makes so manufacturers ensure to control it well. Manufacturers can then use several ways to obtain the pure carrageenan and remove the other ingredients of seaweed. Again, different processes have different costs and produce different grades and types of carrageenans.

Main properties of carrageenans

Carrageenans can be used to thicken liquids.

Each carrageenan type results in different texture, but they do have a few properties in common. First of all, all of them dissolve in hot water. Also, none of them are stable at low pH-values (<4,3) so if you want to use them in those applications you should ensure they cool down quick so they don’t have a chance to break down.

All gels formed by carrageenans are thermo reversible which means that by heating up the gels they will loose their gel-like structure.

Three types of carrageenan

There are various classes of carrageenans and all work slightly differently.  Their differences are mostly due to a difference in ,6-anhydrogalactose content and the amount and distribution of those sulphate groups. The three main types are: kappa (κ), lambda (λ) and iota (ι) carrageenan. Because of their different compositions they behave quite differently and should be used for different applications.


κ-Carrageenan has an ester sulfate content of 25–30% and an amount of anhydrogalactose units corresponding to 28–35%. It can form strong gels in the presence of potassium (K+) ions. The ions will organize themselves around so-called junction zones in the molecules, which can be up to 10 galactose molecules long. These structures result in quite a brittle gel.


The ι–type has the least anhydro-galactose units of the three types discussed here and has a similar content of sulfate groups as the kappa type. It forms gels in the presence of calcium (Ca2+) ions. The calcium ions will sit in the middle and be surrounded by iota-carrageenan molecules on both sides. The gels formed by iota carrageenan tend to be quite flexible.


This type of carrageenan doesn’t have any of the anhydro-galactose and has the highest amount of sulphate groups of the three (32-39%). It is the most soluble of the three, it’s the only one soluble in room temperature water (the other two are only soluble in the presence of sodium salts).

What are carrageenans used for?

Food producers use carrageenans to thicken their foods. You can see them in a lot of different types of dairy products (we’ve written about the use of stabilizers in ice cream before), tofu as well as meats. Carrageenans also help thicken low-fat mayonnaise and dressings. The lower fat content makes them more runny so the carrageenan can prevent that.

Using carrageenan in chocolate milk

A reason for the common use of carrageenans in dairy products is that they can interact with the casein molecules in milk to form a stronger network. Quite extensive research has been done to try and determine the exact mechanism and by now scientists understand quite well what type of interactions occur. If want a more practical example you might want to have a look at the article from Palsgaard (a carrageenan supplier) on the role of carrageenans in chocolate milk (see sources at the bottom of this post).

Safety of carrageenan

Over the past few years reseachers have written a lot of articles written about the safety of carrageenans for the human body. We’re not an expert on the topic so won’t chime in on the discussion, but did come across various seemingly thorough scientific articles on the topic:

Two review articles on in-vitro & in-vivo studies of carrageenan:

James M. McKim, Food additive carrageenan: Part I: A critical review of carrageenan in vitro studies, potential pitfalls, and implications for human health and safety, Crit Rev Toxicol, Early Online: 1–33, 2014 Informa Healthcare USA, Inc. DOI: 10.3109/10408444.2013.861797, ISSN: 1040-8444 (print), 1547-6898 (electronic)

Myra L. Weine, Food additive carrageenan: Part II: A critical review of carrageenan in vivo safety studies, Crit Rev Toxicol, Early Online: 1–26, 2014 Informa Healthcare USA, Inc. DOI: 10.3109/10408444.2013.861798, ISSN: 1040-8444 (print), 1547-6898 (electronic), link

Sources and further reading

A.P. Imeson, 5. Carrageenan, Handbook of hydrocolloids, link

Cohen, S.M., A critical review of the toxicologal effects of carrageenan and processed euchema seaweed on the gastrointestinal tract, (2002), Critical reviews in Toxicology, 32(5):413-444

FAO, 7. Carrageenan, visited 7-July-2018, link (on the production processes of carrageenan)

Necas, J., Bartosikova, L., Carrageenan: a review, (2013), Veterinarni Medicina, link

USDA, Carrageenan Technical Evaluation report, (2011), link

Palsgaard, Technical paper how to make delicious chocolate milk, (2011), link

Saha, D., & Bhattacharya, S. (2010). Hydrocolloids as thickening and gelling agents in food: a critical review. Journal of Food Science and Technology, 47(6), 587–597.

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