Spherification: Ionic Gelation Simulator

Bath & Droplet

Sodium alginate 1.0%

Calcium chloride bath 1.0%

Droplet radius 8.0 mm

Time acceleration 40×

Gelation State

Droplet suspended above bath

Immersion time

0.0 s

Shell thickness

0.00 mm

Liquid core radius

8.00 mm

Gelled fraction

How it works

Spherification (used e.g. by Ferran Adrià's El Bulli) drops a sodium-alginate solution into a calcium-chloride bath. Ca²⁺ ions diffuse into the droplet and ionically cross-link the alginate polymer chains ("egg-box" binding between Ca²⁺ and the polymer's guluronate blocks), turning liquid into gel from the outside in.

The gelled shell grows as a classic diffusion-limited reaction front, following the parabolic law used for oxide-layer and case-hardening growth:

x(t) = √(2·D_eff·t)
shell thickness = min(x(t), R)
core radius(t)  = max(R − x(t), 0)

Here D_eff is the effective diffusion coefficient of Ca²⁺ through the partially-gelled network. It rises with bath calcium concentration (steeper concentration gradient drives faster inward flux, by Fick's first law) and falls as alginate concentration increases (a denser polymer mesh hinders ion transport). Because real gelation takes minutes, the clock here runs at the acceleration factor you set so the whole process is watchable.

Sodium alginate % — higher values build a denser, slower-diffusing gel network (lower D_eff) but a firmer final shell.
Calcium bath % — higher concentration raises the ionic gradient driving diffusion (higher D_eff), gelling the droplet faster.
Droplet radius — a bigger sphere has farther for the front to travel, so it takes roughly R² longer to gel solid.
Once x(t) ≥ R the sphere is fully gelled (no liquid core left) — direct spherification is normally lifted out well before that point, leaving a thin membrane around a still-liquid centre.

Liquid alginate core Gelled shell (cross-linked) Calcium-chloride bath

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