When pouring cold tea essence into a keli shelishi on shabbos why is there no problom of warming a cold liquid?
Answer:
The principle is that a keli sheini, meaning a “secondary vessel” in which the water was not cooked, does not have the power to actually cook cold water. Although the cold water will be brought to the temperature of the hot water, this is therefore not considered a prohibition of cooking.
This is all the more true for tea essence, which has already been “cooked,” but is also true for “uncooked” cold water.
Sources:
Shulchan Aruch 318:13; see also Shemiras Shabbos Kehilchasah 1:53.
