Not all food packing methods are created equal. The USDA explains why when it comes to canning, most foods like it hot.
To raw pack (pictured left), add very hot canning liquid or water to cover raw food, leaving adequate head space. For hot packing (pictured right), boil raw foods 3 to 5 minutes in a saucepan or blancher, then pour into jars.
UNITED STATES DEPARTMENT OF AGRICULTURE
When canning at home, food can be packed in jars using raw-packing or hot-packing. Hot-packing preserves foods' color and shape better, while raw-packing usually is quicker and easier.