Gellan gum is a polysaccharide whose origin differs from that of
other hydrocolloids presented so far. Its rather recent discovery was
the result of industrial research on gum from bacterial fermentation.
Sphingomonas elodea bacteria transform simple sugars, phosphate,
nitrogen and nutrients into chains of more complex sugars. Once the
process has been completed, the microorganisms are eliminated
by pasteurization.

Precipitation in alcohol and acyl group clarification or elimination
processes are applied to the gum to further transform it. Four
derivatives are manufactured in the industry, each with different
properties. Two forms are more widely used in cooking: high-acyl
and low-acyl gellan gum.


HIGH-ACYL GELLAN GUM

High-acyl gellan gum produces a supple, elastic texture, which is
the result of the well-known acyl groups, allowing the formation
of helices that trap water. Upon hydration, the gum is insensitive to
the presence of calcium or sodium ions, which do not significantly
affect the formation of a gel. However, heat is necessary to properly
hydrate the molecule, whereas the presence of sugars or acids in
excessive quantity can interfere with this crucial step. The gel melts
and re-sets at about 158°F to 176°F (70°C to 80°C).


LOW-ACYL GELLAN GUM

Low-acyl gellan gum is more commonly used in molecular
gastronomy to make firm, brittle gels that tolerate temperatures
up to 284°F (140°C). For this reason, it is preferred in the preparation
of hot dishes. However, it must be handled with great care, as it is
significantly more sensitive to the presence of ions than its highacyl
counterpart. Hard water, as well as the presence of sugar or
an acid solution medium, slows down the hydration process, which
requires a higher temperature.

The best way to properly hydrate this product is to mix it with
demineralized water or milk, or use sequestering agents and mix
vigorously. The sequestering agents used are salts (sodium citrate,
sodium hexametaphosphate) which, when dissolved in water,
attach to the ions, making them unavailable for the gum in the
solution and thus allowing it to hydrate at a lower temperature. The
gel forms upon cooling due to the ions present in the food added
to the mixture, or by the addition of other ions such as calcium,
sodium, magnesium or potassium salts. There are a great variety
of solutions with which low-acyl gellan gum can form gels, which
greatly increases its possible uses.