Why Are Cantonese Sauces So Gloopy?

They’re not: You’ve just had bad luck in lackluster cha chaan tengs. It’s a common mistake to think of these overly thickened sauces as an American corruption of Cantonese classics. But sauce thickened with cornstarch is—in moderation—an age-old element of Chinese cooking, an essential ingredient to almost every dish.

All cuisines have their thickening agents. French food has the roux—butter cooked with flour that melts into a sauce, evenly distributing the flour. But a roux needs time to cook into a sauce, a while to thicken up—elements that are antithetical to the lightning-fast cooking times of Cantonese cuisine.

And so the cornstarch slurry was born: a heap of cornstarch mixed with a dose of cold water, and poured into a hot liquid to thicken up a sauce. Unlike a roux, cornstarch doesn’t turn the sauce opaque, and so a Cantonese sauce retains its color and translucency through the thickening process, while also delivering the glossy sheen that’s so important to good fresh Cantonese cooking.

The cornstarch does another great thing: When you toss a cornstarched sauce in a stir-fry it sticks to the meat, coating everything evenly and delivering the same punch of flavor with every bite. Used judiciously, cornstarch doesn’t ruin a dish: it makes it.

The problem is, of course, that not all sauces need to be thickened—and a heavy hand with the cornstarch can easily replace more time-consuming methods of cooking, such as reducing over a low heat. Imagine you’re a harried cook in a low-budget cha chaan teng: When you’re spooning out sauces, it’s in your interest to have an extra ladleful to go around, even if it’s a little sticky and a little low in flavor.

So sure, you throw an extra scoop of cornstarch into the curry sauce. Who’s gonna notice, anyhow?