With the rise of molecular gastronomy the term hydrocolloid has become, shall we say, hot. But what exactly is a hydrocolloid? “Colloid” is a science-y sounding term that simply means one thing dispersed in another. They’re all around us, colloids. There are solid-in-liquid colloids like, say, paint. There are gas-in-liquid colloids (whipped cream), gas-in-solid colloids (styrofoam), liquid-in-liquid colloids (salad dressing), liquid-in-gas colloids (hair spray), the list goes on. A kitchen hydrocolloid, as the name implies, is a colloid that’s based on water or some other mostly-water liquid like juice or broth. Which is to say it’s a colloid where water is the medium that something else is being dispersed in — the “continuous phase” as it’s technically called — and the something else that’s being dispersed (the “dispersed phase”) is a gum or starch or a protein.
All the thickeners we commonly use in the kitchen and that I’ve listed so far — wheat flour, air, fat, pectin, gelatin, cornstarch etc. — are (or can be) hydrocolloids. However that’s not what most people mean when they talk about hydrocolloids these days. Rather they’re referring to a new breed of thickeners/gelling agents which, either by themselves or in combination with others deliver at the very least non-traditional, and at the most highly unusual, results. Like what? Maybe a sauce for a meat dish that has neither the cloudiness nor the starchy mouthfeel of a roux-thickened sauce. Perhaps a custard that has no egg flavor it. Or possibly a plate of clear gel noodles that can be served piping hot.
Modern kitchen hydrocolloids, in essence, are thickeners that give cooks options they never had before. They are highly variable things, ranging from plant derivatives like aloe vera, agar-agar, carrageenan, mastic, locust bean gum and guar gum to fermented thickeners like xanthan gum and gellan gum to sugar derivatives like methyl cellulose. Some thicken when they’re hot, others when they’re cold, some work alone, some need calcium or potassium ions to work. As with thickeners generally, it’s hard to know where to start with hydrocolloids. Frankly a lot of them are of limited use — at least to me. However if there’s a specific hydrocolloid you’re interested in, let me know and I’ll put up something about. Hydrocolloids are hot stuff in the ingredients industry and I’ve had experience with quite a few. If I have an answer to your question I’ll post it!