This article is from the Food Preserving FAQ, by Eric Decker firstname.lastname@example.org with numerous contributions by others.
For all products, if the USDA Home Canning guide only offers processing times
for pint jars, then the product should not be canned in quarts. Usually this
occurs for dense or tightly packed products such as cream style corn, or for
heat-sensitive products such as jelly, mushrooms or pickle relishes. In all
cases, the extra processing time that would be required to insure an adequate
temperature for an adequate time in the coldest part of the jar would be so
long that the quality of the product would be lost. Relishes would be soft
and mushy, corn would be tough, jelly would be syrupy.
Packing food for canning in irregularly-shaped jars such as ketchup bottles
or honey bears is not acceptable. The irregular shape and size might not
allow for normal circulation and heat penetration, and cold spots might exist
that would allow for the survival of bacteria.
If the product has all ready been packed and processed within the last 24
hrs, it may be repacked and reprocessed in smaller jars, or refrigerated.
If it has been longer than 24 hrs since the processing, the product should
be discarded to ensure safety.
Food may be packed and processed in smaller jars, half pint instead of pint
if desired, but the processing time to be used should be that specified for
pints. There is no formula to determine how much less processing would still
be adequate. Mayonnaise or other straight sided, regularly shaped,
commercial packer jars may be used for boiling water bath canning only. They
should not be used for pressure canning, due to the danger of breakage,
particularly when the canner is opened. Flying glass is dangerous.