Odor Coming From Chipboard Flooring?

We had intended to lay a laminate floor in our dining room which includes an under stair cupboard previously used for storage. We laid plywood over the old chipboard floor with PVA and screws. Since then we have been getting an unpleasant odor from the cupboard area but nothing from any of the rest of the floor. We have now lifted the plywood in the cupboard to try and find the source of the smell.

We have sealed the area with PVA but still the smell occurs.

The only thing that had happened sometime in the past was that some cider was spilled in this cupboard. Would this have re-acted with the chipboard flooring? What can we do to get rid of this odor? Until we do, we cannot proceed to lay any new flooring. Any help would be appreciated.

Bill from Gloucester, England