Propylene Glycol Alginate
What it does
Thickener/stabiliser/emulsifier.
How it's made
Modified seaweed alginate.
Propylene glycol alginate (PGA) is a modified seaweed extract used as a thickener, stabiliser and emulsifier; unlike ordinary alginates it works well in acidic conditions, so it is used to stabilise the foam on beer, thicken salad dressings and stabilise acidic drinks and dairy products.
It is made from alginic acid (extracted from brown seaweed) by reacting it with propylene oxide. This attaches propylene glycol groups to the alginate molecule, which changes its behaviour — making it acid-stable and giving it some emulsifying ability that the plain alginates lack.
The modified alginate is purified and dried into a powder. The propylene glycol groups are what let it keep working in the low-pH conditions where ordinary alginates would fail, making it the alginate of choice for beer foam, vinaigrettes and fruit-based products; it remains a seaweed-derived, plant-based ingredient.
Possible reactions
Generally safe.