Carrageenan, extracted from red seaweed, has been used in flavoured milks and dairy desserts for decades. It is also one of the easiest stabilisers to get wrong, because what it does in milk depends on the milk itself.

Three types

Commercial carrageenans are grouped as kappa, iota and lambda. A review of thickening and gelling agents describes how kappa and iota form junction zones between chains and gel, including in milk. Lambda carrageenan does not gel. Which type a product needs depends on whether the job is to add body, to suspend particles or to set.

Why milk changes things

In a study of milk beverage model systems, solutions of kappa-carrageenan in milk were more viscous and more shear-thinning than the same solutions in water. The authors attribute this to the well-known interaction between kappa-carrageenan and casein. Earlier work on milk gels found that in model systems of carrageenan and kappa-casein, calcium promoted gelation.

A study of kappa-carrageenan gels in reconstituted skim milk adds a practical condition. Gel strength depended on the milk solids, the carrageenan and the cations present, and the carrageenan had to be in its disordered, coil form in solution before the mix cooled through its transition temperature for the milk to gel properly. The heat treatment of the milk itself did not affect the interaction. Carrageenan that is not fully dissolved and heated through its transition will not do what the formula expects.

When it goes wrong on the shelf

A study of UHT milk drinks followed carrageenan-stabilised samples through long storage. Three things led to excessive gelation:

  • Severe heating, with more protein denaturation.
  • Lower pH.
  • Kappa in place of iota carrageenan. Kappa forms weaker interactions with milk proteins, which leaves more of it free to link to itself.

The authors suggest that the balance between carrageenan linking to carrageenan and carrageenan linking to protein sets the gel strength, and gel strength rose during storage. A drink that pours well at release can be noticeably thicker months later.

The amount matters as well. In a microscopy study of carrageenan in skim milk, low levels of kappa and iota gave a fine, stranded network of carrageenan and protein, while high levels gave strongly flocculated structures. Adding more carrageenan to cure a sediment can create a different defect.

Processing and flavour

In a study of UHT chocolate milk heated at 145 °C for 6 seconds, kappa-carrageenan was more effective than lambda in limiting fouling of the heat exchanger. And at similar viscosity, kappa-carrageenan milk systems released flavour better than alginate ones in sensory tests.

A practical checklist

  • Decide what the carrageenan is for: body, suspension or a set texture.
  • Make sure it is fully dispersed, dissolved and heated through its transition.
  • Test at the real pH and after the real heat treatment.
  • Store samples at ambient and warm temperatures and check them over the whole shelf life, not only at release.
  • Treat "add more" as a trial arm, not a fix.