Unable to index field in Search API settings in a commerce site
If you go to admin/config/search/search_api, then I guess you could see a server of type "Index".
Click on the Edit link against that and go to the "fields" tab(admin/config/search/search_api/index/product_display/fields).
Enable the checkbox against your new field and save.
You will have to index the whole content, which you can do by click the view tab and clicking the "Index Now" button.
I guess this would do.