very delicious?

"The food was very delicious" is incorrect.

Some adjectives are called "non-gradable". 

They are not normally used with "very" or "a bit", for instance.

These adjectives already have an idea of "perfection" about them. 

Delicious is one (others: ideal, terrified, huge, freezing, fascinated, etc.).

An adverb used in front of these adjectives is "absolutely".

Therefore, The food was absolutely delicious is correct.

*gradable : 형용사가 단계어인(비교급・최상급으로 쓰거나 very, less 등과 함께 쓸 수 있는)

*non-gradable : 형용사가 비교급과 최상급으로 [very, less 같은 말과 함께] 쓸 수 없는

생각해보니 delicious는 비교급이나 최상급이 없다. 이미 아주 맛있는 이란 의미이므로...

very perfect란 말은 쓰지 않는것처럼.

*non-gradable adjective 앞엔 gradable adverb를 쓸 수 없다.

*gradable adverbs

 very / incredibly / extremely / rather / slightly / a bit / awfully / terribly

 *non-gradable  adverbs

 totally / utterly / absolutely / a quite / completely / really

*really can be used with both gradable and non-gradable