What it does
Carboxymethyl groups are attached along the cellulose backbone. They carry a negative charge, which keeps the chains apart and lets water in. The result is a thickener that hydrates quickly in cold water and gives a smooth, non slimy viscosity.
Where it works
Ice cream, where it controls ice crystal growth and gives body without heaviness. Acidified milk drinks, where its charge lets it wrap around casein and stop it aggregating at low pH, which is a job very few other materials do. Also bakery, for water retention in a dough.
Where it does not
It is not a gelling agent and will not build structure on its own. It is also sensitive to calcium, which can precipitate it out of solution.
What it interacts with
Protein, usefully, at low pH. Calcium, unhelpfully. Guar and locust bean gum, beside which it is often used rather than instead of.
