how much moisture or liquids may be on a food when heating up [permissibly] on shabbos
must it be totally dry/ a little moisture/ some oil and dressing / a little ketchup or sauce on chicken etc?
Moisture on food is considered as part of the solid and not like a liquid. Therefore one may reheat chicken or kugel even though it has some oil or moisture on it. However if it is more than just moisture, then it is considered liquid, and should be removed or heated up in place thatit can’t getto yas soledes bo. For example – See Minchas Yitzchok that one who wants to place frozen food on Shabbos on a hot pot should be careful that there isn’t ice or frost on the food because the ice will get cooked. For example, warming a frozen challah on a hot pot, or to put frozen matzoh balls into a hot pot (off the fire), it should be free of ice.
Meohr Hashabbos Michtav 1&2 from R. S. Z. Auerbach, R’ Y. Y. Fisher, Rav Eliyashiv zt”l, R’ Vozner zt”l in a letter at the end of Orchos Shabbos, Minchas Yitzchok 9-31, Rav Y. Cahen shlit”a