The best way to imagine an audit trail is to think of a food safety product recall. If you found out that a specific lot of an organic ingredient was contaminated, you would use your recordkeeping system to determine which final batches of product that ingredient went into. An audit trail is the collection of documents that would allow you to do that.
Your audit trail documents should show the purchase and use of organic products in addition to showing how much finished product was produced and sold. Records should disclose all of your activities and transactions with enough detail to be readily understood and audited.
Records must be available onsite during normal business hours so that authorized state and certifying agents can verify your compliance with the National Organic Program standards. You must maintain records for a minimum of five years.