The jars into which jam is filled should be perfectly dry, and if any drops are spilt on the edges they should be wiped off at once with a cloth dipped in hot water and well wrung out.
The jam can either be covered whilst boiling hot or left until perfectly cold. The former method is to be preferred, as it is more reliable, but the bottles should either be left upside down, or a piece of parchment paper placed on top, otherwise the condensed steam dropping on to the top of the jam will produce mould. A common practice, too, is to put a circular piece of white paper dipped in brandy on top.
After having been thoroughly washed and cleaned, place in a moderately hot oven, resting them on sheets of newspaper. If oven is very hot place newspaper over tops of jars, or leave the door open.