How about "really sour"? Sometimes I'll try an English phrasing that I consider to be more common, even if it risks the wrath of the owl.
What would you say, upon tasting a juice of this type (e.g. lemon juice)? I certainly have no problem with "This juice is very sour" as a correct answer, but I feel like I'd more likely say "This juice is really sour".
I even looked up "really" in SpanishDict.com - the first translation is "muy".
But maybe that would be more accurately expressed in Spanish as "Este jugo es ácido de verdad".