1. The reason why I like it is I can enjoy tasting many ingredients.
2. The reason why I like it is that I can enjoy tasting many ingredients.
3. The reason why I like it is because I can enjoy tasting many ingredients.
(Which one is grammatical? Which one is omitted after 'is' in Sentence 1?)
All of them are grammatical.
In the first sentence, "that" is omitted.