In the previous Halacha, we have explained that one may squeeze a lemon Shabbat by hand, as opposed to using a utensil, for squeezing lemons does not share the same Halacha as squeezing other fruits on Shabbat. We have also mentioned that Maran Rabbeinu Ovadia Yosef zt”l writes that even though according to the letter of the law it is permissible to squeeze lemons on Shabbat, it is preferable to follow the more stringent opinion regarding squeezing lemons into an empty vessel. Therefore, one should first put some sugar into the vessel and only then squeeze the lemon over it, such that the lemon juice will be absorbed by the sugar on contact. In this way, it will be permissible to squeeze lemons on Shabbat according to all opinions.
Maran zt”l writes, however, that although with regards to the prohibition of squeezing on Shabbat one may in fact squeeze lemons on Shabbat, if one squeezes a lemon into tea or any other boiling food on Shabbat, one may be transgressing the prohibition of cooking on Shabbat since the lemon juice becomes cooked upon coming in contact with the tea or the hot food. Thus, one who wishes to prepare tea with lemon on Shabbat should follow the following procedure: Before preparing the tea, one should pour the boiling water into an empty cup thus giving the water the halachic status of “Keli Sheni” (second vessel), meaning that the water is no longer in the “Keli Rishon” (first vessel) that it was boiled in; were it to be in a “Keli Rishon”, it would cause whatever comes in contact with it to be cooked. Once the water is in a “Keli Sheni,” one may then pour this water over the tea essence and lemon juice found in a “Keli Shelishi” (third vessel).
Regarding the aforementioned way of preparing tea through pouring the water from a “Keli Sheni” onto the tea, lemon, and sugar found in another cup, one may even prepare tea using a tea bag that was not pre-cooked on Erev Shabbat, for pouring from a “Keli Sheni” onto tea leaves does not cause a form of cooking that is prohibited on Shabbat. Although one may not place tea leaves directly into the “Keli Sheni” itself on Shabbat for a “Keli Sheni” does cause tea leaves to be cooked, nevertheless, pouring the hot water from a “Keli Sheni” onto tea leaves is permitted for this does not cause the kind of cooking forbidden on Shabbat. G-d-willing, we shall explain the laws of cooking on Shabbat further a different occasion.