A. Headspace is the distance between the surface of food and the underside of the lid. This space allows for the expansion of food solids or bubbling up of liquid during processing. If headspace is not adequate, some food in the container will be forced out, leaving food particles or syrup on the sealing surface and preventing a seal. When too much headspace is allowed, some air may remain in the jar after processing, causing food at the top of the jar to darken. Adequate headspace allows a vacuum to form during the processing of the food.
Life is what happens to you while you're busy making other plans.
- John Lennon