Using salt was a common way to preserve meat and fish at this time. Salt dries the flesh out, and that makes it harder for bacteria to grow. Without refrigeration it had to be packed in a layer of salt to keep it dry. If the meat became damp in the storehouse, it could go rotten. Prosciutto (Italian dry cured pork) is a traditional examples we still use today.
Salt cured meat could also be kept in ‘brine’ (water which is so salty that bacteria can’t grow). Corned beef and pickled pork are still made this way today.
Convicts would have eaten both types of preserved meat.