The create ingredient dialog allows you to create an ingredient on the fly. See the following image.
Enter the name of the ingredient into the "Name" field. You must also enter the minimum purchase quantity and unit, along with the usage unit. Click the "OK" button and the ingredient will be created and inserted into the current grid.
This dialog can be launched from the Search/Select dialog and/or the search and ingredient pages of the various Rollup windows.
NOTE: When you create an ingredient on the fly, it will automatically be flagged as incomplete. At some point you will have to complete all details for the ingredient. i.e. set up category and supplier links.