Shabbat 51 - Warm food on Shabbat
Earlier we saw that there is a prohibition to wrap, or insulate hot pot of food on Shabbat. Before it is night, one should not use materials that add heat, and on Shabbat itself - not even materials that don’t add heat.
However, that only applies if he did not wrap his pot while it was yet day. If he did, then even if the pot became uncovered, he can cover it again. Why? The whole reason for wrapping prohibition is so that he would not rake the coals and would not reheat the pot, if he finds that it has somewhat cooled off. If there is no such suspicion, accordingly, there is no prohibition.
Therefore, if he poured the food into another, different container, then he can wrap one. The logic here is that he already cooled the food off by pouring it into another container, so certainly he won’t reheat that new container.
In a similar vein, one may wrap cold food so that they stay cold, and even to take the chill off - again, for the reason that there is no prohibition to stop him from doing.
Art: Jean-Baptiste-Simeon Chardin - Leeks, a casserole with a cloth, a copper pot and cover, an onion and eggs with a pestle and mortar, on a stone ledge