The savory richness of the beef bouillon enhances the umami of the ground beef while the herbs, seasonings, and aromatics add earthy and savory flavors that you would have probably added in anyway — the au jus is basically a one‑stop shop for flavorful burgers that saves you the trouble of prepping and adding in separate seasonings.
Using au jus mix is such a clever umami bomb! I usually just hit mine with a heavy hand of coarse salt and black pepper. Do you think the cornstarch in the packet changes the sear on the meat?
That's probably something I'd only mix in for pan burgers as a change-up, would probably help the texture and make it more like a meatloaf / salisbury steak
For grilling use this stuff, big cheap canisters, you'll never look back