Which materials have a negative quantity in a bill of materials or in a recipe?

In a bill of materials or a recipe, by-products are materials that are generated as a secondary result of the production process but are not the primary output. They can have a negative quantity because they represent materials that are produced in lesser amounts alongside the main product. By-products often occur during the manufacturing of a primary product, and setting them to a negative quantity allows for their accounting within the overall production framework, typically indicating a value that must be subtracted from the total or managed as an additional output.

Understanding that by-products are usually incidental allows for better planning and more accurate cost assessments in production processes. They can be sold, reused, or discarded, and specifying them as negative helps to reflect their true contribution to the production balance sheet or recipe.

On the other hand, bulk materials usually do not have a negative quantity because they are the primary materials used in production. Co-products, while they are significant outputs of a process, are typically accounted for as separate, standalone products and do not warrant negative quantities in the same way. Waste products indicate materials lost in the process but are treated separately and do not represent a productive output in the same manner as by-products do.