If you have no clue what it is I recommend head space analysis. After you have collected the volatiles you inject the concentrate into a GC (GC MS) to identify the chemical and based on that you can either remove or mask it.

Thank you Doctor, I will try the head space analysis.

Odor can be modified with Maillard reaction. Maillard reaction is a non-enzymatic reaction between carbonyl groups of reducing sugars and amino groups of amino acids, peptides or proteins.