Mongoose. Remove fields on save that are not present in schema

I have a doc saved in MongoDB like this: { title: 'title', author: 'author name', body: 'the body', admin: 'admin user' } And this is the schema in Mongoose: var blogSchema = new Schema({ title: String, author: String, body: String }); I would like that on save, the "admin" field was removed from the doc, is this possible? Can I automatize this in event pre-save? Thanks.