Regarding the laws of cooking and warming food on Shabbat, Halacha assigns different statuses to various kinds of utensils. The pot in which food had been cooked is called a “Keli Rishon” (“first utensil”). One may not place food in a Keli Rishon, even after it has been removed from the fire, so long as the pot is still hot. If, however, one poured the contents of the Keli Rishon into a different utensil, that utensil assumes the status of a “Keli Sheni” (“second utensil”), in which, generally speaking, cooking is permissible. Certain items, however, such as tea, may not be cooked in a “Keli Sheni.” Therefore, if one wishes to make tea he must pour the water into a third utensil – a “Keli Shelishi” – and then place the teabag.
An interesting question arises concerning liquid that one transferred from a pot with a ladle. Consider, for example, the case of a pot of hot water that one left on the blech before Shabbat. If on Shabbat he draws water from the pot with a ladle, and pours the water from the ladle into a cup, does that cup have the status of a “Keli Sheni,” or a “Keli Shelishi”? On the one hand, the ladle is certainly a separate utensil, and we might therefore assume that it constitutes a “Keli Sheni,” rendering the teacup a “Keli Shelishi.” If so, then one may insert the teabag into that cup. On the other hand, one might argue that since the ladle entered the pot on the blech and drew the water from there, perhaps it assumes the status of a “Keli Rishon.” It would thus be forbidden to place the teabag into the cup; one would have to transfer the water into a different cup and then insert the teabag.
Hacham Ben Sion Abba Shaul (Israel, 1923-1998) distinguished in this regard between a “Keli Rishon” on the fire and a “Keli Rishon” that had been removed the fire. If one draws water from a pot on the fire, then we treat the ladle as a “Keli Rishon,” and therefore the cup into which one pours from the ladle will be a “Keli Sheni.” In such a case, then, one must pour the water into a different cup before placing the teabag. If, however, one first removed the pot from the fire, then we may treat the ladle as a “Keli Sheni,” such that the cup into which the water is poured from the ladle will have the status as a “Keli Shelishi.” It would therefore be permissible to place the teabag into that cup.
A different question arises in a case where one uses a ladle to serve several bowls of soup, and bring the ladle back and forth into and from the pot. One might think to forbid returning the ladle into the pot, since invariably some droplets remain on the ladle after the soup has been poured into the bowl, and these droplets are then cooked when the ladle is returned to the pot. In truth, however, this is permissible. Both Rabbi Moshe Halevi (Israel, 1961-2001), in his work Menuhat Ahaba, and Hacham Ovadia Yosef, rule that one may return the ladle to the pot without first drying it, as we are not concerned about the tiny droplets on the ladle.
Summary: If one draws hot water from a pot on the fire with a ladle and then pours the water from the ladle into a cup, he may not place a teabag into that cup; he must first transfer the water to a different cup. If, however, the pot of water was off the fire, and one then draws water with a ladle and pours it into a cup, he may place a teabag in that cup. One who served soup from a pot with a ladle may use the ladle thereafter to draw more soup from the pot, despite the fact that the droplets on the ladle will be reheated in the pot.