You can find other Vowelburgers™ Riddles here.
Once a restaurant renowned for its delectable burgers, the customers of the Old Consonant's Diner have been noticing the quality of food slowly slipping away. Finally, a day of reckoning has come: the town's newspaper has sent a food critic over to the establishment to investigate.
In unassuming clothing, the critic walks in, and for lunch, orders a five-Vowelburger™ flight. It's soon brought out, with identical ingredients except for the five patties -- A, E, I, O, and U, in a random order. Indiscreetly consuming a bit of each, the critic then pays for his meal and take his leave to pen down his notes.
That afternoon, the critic's review runs in the local newspaper, providing commentary on the five Vowelburgers™ in the flight from left to right:
0* Awful chemical aftertaste, reminds me of that dye that's trending these days. At least that makes your hair more shiny.
4* A burger that almost makes the place appear decent. Don't look to the left or the right, though.
1* A slop the consistency of a meat smoothie. Send it back to its maker.
2* I can only give a "??" for this one.
1.5* Have I lost my sense of taste? Or is this patty's flavor more lacking than the last time I was here?
"That second patty's the key!" cries the manager to the cooks that evening after the restaurant closes its doors. "We're going to need to frame all our patty recipes around that one for the future. Which letter patty was it again?"
"Sir," says one of the cooks after a long pause, "you fired the cook who made the burgers on the flight this afternoon. Now we don't know which order the patties were in, nor the burgers' ingredients."
"You're kidding," says the manager. "Find me that patty order, or this place shuts down tomorrow. Period."