Funny, I was reading an article from abroad today and the guys were saying that the McDonald’s Coke over there is really good…
Here in Brazil I’ve never ordered Coke at McDonald’s because I think that refill Coke is really bad. It’s always that old Coke with no fizz and watered down.
The foreigners say that over there it’s much better because Coca‑Cola and McDonald’s have had an agreement from the beginning that their Coke has to be delivered specially in steel containers, and not in plastic ones like for all the other Coca‑Cola customers.
And that protects it from the sun and other factors.
I don’t know what McDonald’s Coke is like in other cities. But the one here is undrinkable.

Source: https://www.allrecipes.com/article/why-mcdonalds-coke-tastes-better-than-all-others/