How to Thicken with Cornstarch
It has a weakness, okay? It’s a dramatic little starch. If you boil it for too long—like, more than a few minutes—it can break down and turn your perfect sauce back into a watery mess again. So work fast.
Also, it hates acids. If you’re making a lemon chicken or a vinegar-based sauce, cornstarch is a bit unreliable. It’s like bringing a floppy umbrella to a hurricane. In that case, consider using arrowroot powder or potato starch instead. They’re more chill with acidic ingredients.
Cornstarch slurry how to thicken a sauce – Artofit