Sodium citrate is the salt behind silky cheese sauce: a small amount lets cheese melt into a smooth, glossy, non-greasy sauce without splitting. It also buffers acidity, which is what lets acidic juices be spherified, and gives sparkling drinks their tang.
PAIR's modernist science — how much to use, how it behaves with heat, and what makes it fail — is a Pro feature. The description, nutrition, history and facts stay free.