Cal. Health & Safety Code § 112125

Except when sold in bulk for manufacturing purposes, it is unlawful to sell or otherwise dispose of at retail jams, jellies, preserves, marmalades, peanut butter, horse-radish, mayonnaise, or salad dressings other than in closed containers approved by the department, when the department determines that any other method of sale or disposition of any such food or food product is conducive to its contamination by flies, insects, dust, dirt, or foreign material of any kind whatsoever.