Silicon Dioxide (amorphous)
What it does
Anti-caking in powders.
How it's made
Purified synthetic silica.
This entry refers specifically to the amorphous (non-crystalline) form of silicon dioxide used in food, emphasising that the food-grade material is not the crystalline quartz found in sand and rock. Its jobs are the same: keeping powders free-flowing and dry as an anti-caking agent, and sometimes carrying flavours or acting as a filter aid.
It is produced synthetically to guarantee the amorphous structure. In the fumed process a volatile silicon compound is burned in a flame, condensing into ultra-fine chains of silica particles; in the precipitated process, acid is added to a sodium silicate solution so that silica comes out of solution as a fine powder. Neither route produces the crystalline form.
After manufacture the silica is washed to remove salts, dried and milled. The resulting light, porous powder has a very large surface area, which is precisely what allows a small amount to absorb moisture and coat the particles of a food powder so it does not cake.
Possible reactions
Generally inert and safe.